Pioneer Multi Asset Floating Rate Fund

Neither the Securities and Exchange Commission nor any state securities agency has approved or disapproved the fund’s shares or determined whether this prospectus is accurate or complete. Any representation to the contrary is a crime.

This table describes the fees and expenses that you may pay if you buy and hold shares of the fund.

You may qualify for sales charge discounts if you or your family invest, or agree to invest in the future, at least $50,000 in Class A shares of the Pioneer funds. More information about these and other discounts is available from your investment professional and in the “Sales Charges” section of the prospectus beginning on page 37 and the “Sales Charges” section of the statement of additional information beginning on page 72.

This example is intended to help you compare the cost of investing in the fund with the cost of investing in other mutual funds. The example assumes that you invest $10,000 in the fund for the time periods shown and then, except as indicated, redeem all of your shares at the end of those periods. It also assumes that (a) your investment has a 5% return each year and (b) the fund’s total annual operating expenses remain the same except for year one (which considers the effect of the expense limitation). Although your actual costs may be higher or lower, based on these assumptions your costs would be:

The fund pays transaction costs, such as commissions, when it buys and sells securities (or “turns over” its portfolio). A higher portfolio turnover rate may indicate higher transaction costs and may result in higher taxes when fund shares are held in a taxable account. These costs, which are not reflected in annual fund operating expenses or in the example, affect the fund’s performance.

Normally, the fund invests at least 80% of its net assets (plus the amount of borrowings, if any, for investment purposes) in floating rate instruments of U.S. and non-U.S. issuers, including: senior secured loans (“senior loans”) and second lien or other subordinated or unsecured loans; debt issued by banks and other corporate, governmental and non-governmental entities; corporate bonds; mortgage-backed and asset-backed securities; event-linked bonds (also known as “catastrophe bonds”); and preferred stock. The fund also considers as floating rate instruments, and the fund may invest without limit in, adjustable rate securities, fixed rate securities with durations of less than or equal to one year, funds that invest primarily in floating rate instruments, and fixed rate securities with respect to which the fund has entered into derivative instruments to effectively convert the fixed rate interest payments into floating rate interest payments. The fund considers these investments as economic equivalents of floating rate instruments.

The fund may invest up to 20% of its net assets in debt securities that are rated below investment grade (debt securities rated below investment grade are commonly referred to as “junk bonds”) or are unrated but determined by the fund’s investment adviser to be of equivalent credit quality, and those that are in default or in bankruptcy. The fund does not have a policy of maintaining a specific average credit quality of its portfolio.

In addition to its investments in floating rate instruments, the fund also may invest in other securities, including debt of U.S. and non-U.S. governmental, corporate and other non-governmental issuers; mortgage-backed and asset-backed securities; convertible securities; bonds not paying current income; bonds that do not make regular interest payments; zero coupon securities; money market instruments; and other short-term investments, including cash and cash equivalents, certificates of deposit, repurchase agreements maturing in one week or less and bankers’ acceptances. The fund may receive debt securities or equity securities as a result of the general restructuring of the debt of an issuer, the restructuring of a floating rate loan, or as part of a package of securities acquired with a loan.

The fund does not have a targeted maturity range for its portfolio. The fund invests in securities with a broad range of maturities. The fund’s investments may have fixed or variable principal payments and all types of interest rate and dividend payment and reset terms, including fixed rate, adjustable rate, floating rate, contingent, deferred, payment in kind and auction rate features. The fund’s investments may include instruments that allow for balloon payments or negative amortization payments.

The fund may invest in equity securities, including common stocks, rights, warrants, depositary receipts, exchange-traded funds (ETFs) that invest primarily in equity securities and equity interests in real estate investment trusts (REITs). The fund may invest in equity securities as a consequence of holding debt of the same issuer, when the adviser believes they offer the potential for capital gains or for other portfolio management purposes, although equity securities may not pay dividends or contribute to achieving the fund’s investment objective of a high level of current income.

The adviser considers both broad economic and issuer specific factors in selecting a portfolio designed to achieve the fund’s investment objectives. In assessing the appropriate maturity, rating, sector and country weightings of the fund’s portfolio, the adviser considers a variety of factors that are expected to influence economic activity and interest rates. These factors include fundamental economic indicators, such as the rates of economic growth and inflation, Federal Reserve monetary policy, and the relative value

of the U.S. dollar compared to other currencies. Once the adviser determines the preferable portfolio characteristics, the adviser selects individual securities based upon the terms of the securities (such as yields compared to U.S. Treasuries or comparable issues), liquidity, credit quality, and sector and issuer diversification. The adviser also employs fundamental quantitative and qualitative research to assess an issuer’s credit quality, taking into account financial condition and profitability, future capital needs, potential for change in rating, industry outlook, the competitive environment and management capabilities. The adviser may sell a portfolio security when it believes the security no longer will contribute to meeting the fund’s investment objectives. The adviser makes that determination based on the same criteria it uses to select portfolio securities.

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective. Following is a summary description of principal risks of investing in the fund.

Market risk. The values of securities held by the fund may fall due to general market conditions, such as real or perceived adverse economic, political, or regulatory conditions, inflation, changes in interest or currency rates or adverse investor sentiment. Adverse market conditions may be prolonged and may not have the same impact on all types of securities. The values of securities may fall due to factors affecting a particular issuer, industry or the securities market as a whole. The recent global financial crisis has caused a significant decline in the value and liquidity of many securities, including securities held by the fund. In response to the crisis, the U.S. government and the Federal Reserve have taken steps to support financial markets. The withdrawal of this support could also negatively affect the value and liquidity of certain securities. In addition, legislation recently enacted in the U.S. calls for changes in many aspects of financial regulation. The impact of the legislation on the markets, and the practical implications for market participants, may not be known for some time. The fund may experience a substantial or complete loss on any individual security.

High yield or “junk” bond risk. Debt securities that are below investment grade, “junk bonds,” are speculative, have a higher risk of default or are already in default, tend to be less liquid and are more difficult to value than higher grade securities. Junk bonds tend to be volatile and more susceptible to adverse events and negative sentiments.

Interest rate risk. Interest rates may go up, causing the value of the fund’s investments to decline (this risk may be greater for securities with longer maturities).

The values of securities with floating interest rates generally are less sensitive to interest rate changes but may decline in value if their interest rates do not rise as much, or as quickly, as prevailing interest rates. Unlike fixed rate securities, floating rate securities generally will not increase in value if interest

rates decline. Changes in interest rates also will affect the amount of interest income the fund earns on its floating rate investments. Unlike fixed rate securities, when prevailing interest rates decrease, the interest rate payable on floating rate investments will decrease.

Credit risk. If an issuer or guarantor of a security held by the fund or a counterparty to a financial contract with the fund defaults on its obligation to pay principal and/or interest, has its credit rating downgraded or is perceived to be less creditworthy, or the credit quality or value of any underlying assets declines, the value of your investment will decline. Credit risk is broadly gauged by the credit ratings of the securities in which the fund invests. However, ratings are only the opinions of the companies issuing them and are not guarantees as to quality. Junk bonds have a higher risk of default or are already in default and are considered speculative.

Prepayment or call risk. During periods of declining interest rates, the issuer of a security (or borrowers in a pool of loans) may prepay principal earlier than scheduled, forcing the fund to reinvest in lower yielding securities. The fund also may lose any premium it paid on the security.

Liquidity risk. Some securities held by the fund may be difficult to sell, or illiquid, particularly during times of market turmoil. Illiquid securities also may be difficult to value. If the fund is forced to sell an illiquid asset to meet redemption requests or other cash needs, the fund may be forced to sell at a loss.

An intermediate participant between the fund and the borrower in a loan participation may fail to meet its obligations to the fund to enforce any rights against the borrower. In addition, the issuer of the loan may default on its obligations.

Risk of insufficient collateral. The value of collateral, if any, securing a floating rate loan can decline, and may be insufficient to meet the issuer’s

obligations or may be difficult to liquidate. In addition, the fund’s access to collateral may be limited by bankruptcy or other insolvency laws.

Risk of disadvantaged access to confidential information. The adviser’s decision not to receive material, non-public information about an issuer of a loan either held by, or considered for investment by, the fund, under normal circumstances could place it at a disadvantage, relative to other loan investors, in assessing a loan or the loan’s issuer, and adversely affect the fund’s investment performance.

Risks of subordinated securities. A holder of securities that are subordinated or “junior” to more senior securities of an issuer is entitled to payment after holders of more senior securities of the issuer. Subordinated securities are more likely to suffer a credit loss than non-subordinated securities of the same issuer, any loss incurred by the subordinated securities is likely to be proportionately greater, and any recovery of interest or principal may take more time. As a result, even a perceived decline in creditworthiness of the issuer is likely to have a greater impact on them.

Risks of non-U.S. investments. Investing in non-U.S. issuers may involve unique risks compared to investing in securities of U.S. issuers. These risks are more pronounced for issuers in emerging markets or to the extent that the fund invests significantly in one region or country. These risks may include different financial reporting practices and regulatory standards, less liquid trading markets, currency risks, changes in economic, political, regulatory and social conditions, sustained economic downturns, tax burdens, and investment and repatriation restrictions.

U.S. government agency obligations risk. The fund invests in obligations issued by agencies and instrumentalities of the U.S. government. Government sponsored entities such as Federal National Mortgage Association (Fannie Mae), Federal Home Loan Mortgage Corporation (Freddie Mac) and the Federal Home Loan Banks (FHLBs), although chartered or sponsored by Congress, are not funded by congressional appropriations and the debt and mortgage-backed securities issued by them are neither guaranteed nor issued by the U.S. government. Although the U.S. government has provided financial support to Fannie Mae and Freddie Mac in the past, there can be no assurance that it will support these or other government sponsored entities in the future.

Mortgage-related and asset-backed securities risk. The value of mortgage-related and asset-backed securities will be influenced by factors affecting the housing market and the assets underlying such securities. As a result, during periods of declining asset value, difficult or frozen credit markets, swings in interest rates, or deteriorating economic conditions, mortgage-related and asset-backed securities may decline in value, face valuation difficulties, become more volatile and/or become illiquid. Additionally, during such periods and also under normal conditions, these securities are also subject to prepayment and call risk. Some of these

securities may receive little or no collateral protection from the underlying assets and are thus subject to the risk of default. The risk of such defaults is generally higher in the case of mortgage-backed investments that include so-called “sub-prime” mortgages. The structure of some of these securities may be complex and there may be less available information than for other types of debt securities. Upon the occurrence of certain triggering events or defaults, the fund may become the holder of underlying assets at a time when those assets may be difficult to sell or may be sold only at a loss.

Risks of inverse floating rate obligations. The interest rate on inverse floating rate obligations will generally decrease as short-term interest rates increase, and increase as short-term rates decrease. Due to their leveraged structure, the sensitivity of the market value of an inverse floating rate obligation to changes in interest rates is generally greater than a comparable long-term bond issued by the same issuer and with similar credit quality, redemption and maturity provisions. Inverse floating rate obligations may be volatile and involve leverage risk.

Risk of investment in other funds. Investing in other investment companies subjects the fund to the risks of investing in the underlying securities or assets held by those funds. When investing in another fund, the fund will bear a pro rata portion of the underlying fund’s expenses, in addition to its own expenses. Although the amount of investment in other funds is limited by legal or tax considerations in certain circumstances, the fund may invest extensively in other funds under certain rules and other forms of relief.

Derivatives risk. Using derivatives exposes the fund to additional risks, may increase the volatility of the fund’s net asset value and may not provide the result intended. Derivatives may have a leveraging effect on the fund’s portfolio. Changes in a derivative’s value may not correlate well with the referenced asset or metric. The fund also may have to sell assets at inopportune times to satisfy its obligations. Derivatives may be difficult to sell, unwind or value, and the counterparty may default on its obligations to the fund. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet known and may not be known for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance.

Credit default swap risk. Credit default swap contracts, a type of derivative instrument, involve special risks and may result in losses to the fund. Credit default swaps may in some cases be illiquid, and they increase credit risk since the fund has exposure to both the issuer of the referenced obligation and the counterparty to the credit default swap. The absence of a central exchange or market for swap transactions led, in some instances, to difficulties in trading and valuation, especially in the event of market disruptions. Recent legislation, noted above, will require most swaps to be executed through a centralized exchange or regulated facility and be cleared through a regulated clearinghouse. The swap market could be disrupted or limited as a result of this legislation, which could adversely affect the fund. Moreover, the establishment of a centralized exchange or market for swap transactions may not result in swaps being easier to trade or value.

Leveraging risk. The value of your investment may be more volatile and other risks tend to be compounded if the fund borrows or uses derivatives or other investments that have embedded leverage. Leverage generally magnifies the effect of any increase or decrease in the value of the fund’s underlying assets or creates investment risk with respect to a larger pool of assets than the fund would otherwise have. Engaging in such transactions may cause the fund to liquidate positions when it may not be advantageous to do so to satisfy its obligations or meet segregation requirements.

Equity securities risk. Equity securities represent an ownership interest in an issuer, rank junior in a company’s capital structure to debt securities and consequently may entail greater risk of loss than debt securities. Equity securities are subject to the risk that stock prices may rise and fall in periodic cycles and may perform poorly relative to other investments. This risk may be greater in the short term.

Risks of zero coupon bonds and payment in kind securities. Zero coupon bonds and payment in kind securities may be more speculative and may fluctuate more in value than securities which pay income periodically and in cash. In addition, applicable tax rules require the fund to accrue and pay out its imputed income from such securities annually as income dividends. Such distributions may be taxable to shareholders.

Portfolio selection risk. The adviser’s judgment about the quality, relative yield, relative value or market trends affecting a particular sector or region, market segment, security or about interest rates generally may prove to be incorrect.

Risk of increase in expenses. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses”

for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

An investment in the fund is not a bank deposit and is not insured or guaranteed by the Federal Deposit Insurance Corporation or any other government agency.

Since the fund does not yet have a full calendar year of operations, it does not disclose any performance information in this prospectus. The performance information provided by the fund in the future will give some indication of the risks of an investment in the fund by showing changes in the fund’s performance from year to year and by showing how the fund’s average annual returns compare with those of a broad measure of market performance.

You may purchase, exchange or sell (redeem) shares each day the New York Stock Exchange is open through your financial intermediary or, for accounts held directly with the fund, by contacting the fund’s transfer agent in writing or by telephone (Pioneer Investment Management Shareholder Services, Inc., P.O. Box 55014, Boston, MA 02205-5014, tel. 1-800-225-6292).

Your initial investment for Class A or Class C shares must be at least $1,000. Additional investments must be at least $100 for Class A shares and $500 for Class C shares. The initial investment for Class Y shares must be at least $5 million. This amount may be invested in one or more of the Pioneer mutual funds that currently offer Class Y shares. There is no minimum additional investment amount for Class Y shares.

The fund intends to make distributions that may be taxed as ordinary income or capital gains.

If you purchase the fund through a broker-dealer or other financial intermediary (such as a bank), the fund and its related companies may pay the intermediary for the sale of fund shares and related services. These payments may create a conflict of interest by influencing the broker-dealer or other intermediary and your salesperson or investment professional to recommend the fund over another investment. Ask your salesperson or investment professional or visit your financial intermediary’s website for more information.

The fund seeks a high level of current income. Capital appreciation is a secondary objective. The fund’s investment objectives may be changed without shareholder approval. The fund will provide notice prior to implementing any change to its investment objectives.

The fund will provide written notice to shareholders at least 60 days prior to any change to the requirement that it invest at least 80% of its assets in floating rate investments.

The fund may invest up to 20% of its net assets in debt securities that are rated below investment grade (debt securities rated below investment grade are commonly referred to as “junk bonds”) or are unrated but determined by Pioneer Investment Management, Inc. (Pioneer), the fund’s investment adviser, to be of equivalent credit quality, and those that are in default or in bankruptcy. The fund does not have a policy of maintaining a specific average credit quality of its portfolio.

The fund may invest up to 35% of its total assets in debt securities of non-U.S. issuers, including emerging market issuers. The fund does not currently intend to invest more than 25% of its total assets in any one non-U.S. country. The fund does not count securities of Canadian issuers against the limit on investment in securities of non-U.S. issuers.

maturing in one week or less and bankers’ acceptances. The fund may receive debt securities or equity securities as a result of the general restructuring of the debt of an issuer, the restructuring of a floating rate loan, or as part of a package of securities acquired with a loan.

The fund may use derivatives, such as credit default swaps, for a variety of purposes, including: as a hedge against adverse changes in the market price of securities, interest rates or currency exchange rates; as a substitute for purchasing or selling securities; and to increase the fund’s return as a non-hedging strategy that may be considered speculative. The fund includes investments in derivative instruments related to floating rate instruments, such as derivative instruments that effectively convert interest payments with respect to fixed rate securities into floating rate interest payments, in determining compliance with the requirement that the fund invest at least 80% of its net assets in floating rate instruments of U.S. and non-U.S. issuers. The fund may invest without limit in derivative instruments.

The fund may invest in equity securities, including common stocks, rights, warrants, depositary receipts, exchange-traded funds (ETFs) that invest primarily in equity securities and equity interests in real estate investment trusts (REITs). The fund may invest in equity securities as a consequence of holding debt of the same issuer, when Pioneer believes they offer the potential for capital gains or for other portfolio management purposes, although equity securities may not pay dividends or contribute to achieving the fund’s investment objective of a high level of current income.

Pioneer considers both broad economic and issuer specific factors in selecting a portfolio designed to achieve the fund’s investment objectives. In assessing the appropriate maturity, rating, sector and country weightings of the fund’s portfolio, Pioneer considers a variety of factors that are expected to influence economic activity and interest rates. These factors include fundamental economic indicators, such as the rates of economic growth and inflation, Federal Reserve monetary policy, and the relative value of the U.S. dollar compared to other currencies. Once Pioneer determines the preferable portfolio characteristics, Pioneer selects individual securities based upon the terms of the securities (such as yields compared to U.S. Treasuries or comparable issues), liquidity, credit quality, and sector and issuer diversification.

Pioneer also employs fundamental quantitative and qualitative research to assess an issuer’s credit quality, taking into account financial condition and

profitability, future capital needs, potential for change in rating, industry outlook, the competitive environment and management capabilities. Pioneer may sell a portfolio security when it believes the security no longer will contribute to meeting the fund’s investment objectives. Pioneer makes that determination based on the same criteria it uses to select portfolio securities. In making these portfolio decisions, Pioneer relies on the knowledge, experience and judgment of its staff and the staff of its affiliates who have access to a wide variety of research.

Floating rate investments are securities and other instruments with interest rates that adjust or “float” periodically based on a specified interest rate or other reference and include repurchase agreements, money market securities and shares of money market and short-term bond funds.

Floating rate loans are made by banks and other financial institutions to large corporate customers. The rates of interest on the loans adjust periodically by reference to a base lending rate, such as the London Interbank Offered Rate (LIBOR), a designated U.S. bank’s prime or base rate or the overnight federal funds rate, plus a premium. Some loans reset on set dates, typically every 30 to 90 days, but not to exceed one year. Other loans reset periodically when the underlying rate resets.

In most instances, the fund’s investments in floating rate loans will hold a senior position in the capital structure of the borrower. Having a senior position means that, if the borrower becomes insolvent, senior debtholders, like the fund, will be paid before subordinated debtholders and stockholders of the borrower. Senior loans typically are secured by specific collateral.

Floating rate loans typically are structured and administered by a financial institution that acts as an agent for the holders of the loan. Loans can be acquired directly through the agent, by assignment from another holder of the loan, or as a participation interest in the loan. When the fund is a direct investor in a loan, the fund may have the ability to influence the terms of the loan, although the fund does not act as the sole negotiator or originator of the loan. Participation interests are fractional interests in a loan issued by a lender or other financial institution. When the fund invests in a loan participation, the fund does not have a direct claim against the borrower and must rely upon an intermediate participant to enforce any rights against the borrower.

Securities in the lowest category of investment grade (i.e., BBB) are considered to have speculative characteristics.

The fund may invest in debt securities rated below investment grade or, if unrated, of equivalent quality as determined by Pioneer. A debt security is below investment grade if it is rated BB or lower by Standard and Poor’s Financial Services LLC or the equivalent rating by another nationally recognized statistical rating organization or determined to be of equivalent credit quality by Pioneer. Debt securities rated below investment grade are commonly referred to as “junk bonds” and are considered speculative. Below investment grade debt securities involve greater risk of loss, are subject to greater price volatility and are less liquid, especially during periods of economic uncertainty or change, than higher quality debt securities. Below investment grade securities also may be more difficult to value.

For purposes of the fund’s credit quality policies, if a security receives different ratings from nationally recognized statistical rating organizations, the fund will use the rating chosen by the portfolio manager as most representative of the security’s credit quality. The ratings of nationally recognized statistical rating organizations represent their opinions as to the quality of the securities that they undertake to rate and may not accurately describe the risks of the securities. A rating organization may have a conflict of interest with respect to a security for which it assigns a quality rating. In addition, there may be a delay between a change in the credit quality of a security or other asset and a change in the quality rating assigned to the security or other asset by a rating organization. If a rating organization changes the quality rating assigned to one or more of the fund’s portfolio securities, Pioneer will consider if any action is appropriate in light of the fund’s investment objectives and policies. An investor can still lose significant amounts when investing in investment grade securities.

The fund may invest in securities of non-U.S. issuers, including securities of emerging market issuers. Non-U.S. securities may be issued by non-U.S. governments, banks or corporations, or private issuers, and certain supranational organizations, such as the World Bank and the European Union.

The fund may invest in U.S. government securities. U.S. government securities include obligations: directly issued by or supported by the full faith and credit of the U.S. government, like Treasury bills, notes and bonds and Government National Mortgage Association certificates; supported by the right of the issuer to borrow from the U.S. Treasury, like those of the Federal Home Loan Banks; supported by the discretionary authority of the U.S. government to purchase the agency’s securities like those of the Federal National

Mortgage Association; or supported only by the credit of the issuer itself, like the Tennessee Valley Authority.

The fund may invest in second lien and other securities that are subordinated or “junior” to more senior securities of the issuer. The investor in a subordinated security of an issuer is entitled to payment after other holders of debt in that issuer.

The fund may invest in mortgage-backed securities. Mortgage-backed securities may be issued by private issuers, by government-sponsored entities such as the Federal National Mortgage Association (Fannie Mae) or Federal Home Loan Mortgage Corporation (Freddie Mac) or by agencies of the U.S. government, such as the Government National Mortgage Association (Ginnie Mae). Mortgage-backed securities represent direct or indirect participation in, or are collateralized by and payable from, mortgage loans secured by real property. The fund’s investments in mortgage-related securities may include mortgage derivatives and structured securities.

The fund may invest in collateralized mortgage obligations (CMOs). A CMO is a mortgage-backed bond that is issued in multiple classes, each with a specified fixed or floating interest rate and a final scheduled distribution date. The holder of an interest in a CMO is entitled to receive specified cash flows from a pool of underlying mortgages or other mortgage-backed securities. Depending upon the category of CMO purchased, the holder may be entitled to payment before the cash flow from the pool is used to fund other CMOs or, alternatively, the holder may be paid only to the extent that there is cash remaining after the cash flow has been used to fund other CMOs first. A subordinated interest may serve as a credit support for the senior securities purchased by other investors.

The fund may invest in asset-backed securities. Asset-backed securities represent participations in, or are secured by and payable from, assets such as installment sales or loan contracts, leases, credit card receivables and other categories of receivables. The fund’s investments in asset-backed securities may include derivative and structured securities.

The fund may invest in asset-backed securities issued by special entities, such as trusts, that are backed by a pool of financial assets. The fund may invest in collateralized debt obligations (CDOs), which include collateralized bond obligations (CBOs), collateralized loan obligations (CLOs) and other similarly structured securities. A CDO is a trust backed by a pool of fixed income securities. The trust typically is split into two or more portions, called tranches, which vary in credit quality, yield, credit support and right to repayment of principal and interest. Lower tranches pay higher interest rates but represent lower degrees of credit quality and are more sensitive to the rate of defaults in the pool of obligations.

The fund may invest in “event-linked” bonds, which sometimes are referred to as “insurance-linked” or “catastrophe” bonds. Event-linked bonds are debt obligations for which the return of principal and the payment of interest are contingent on the non-occurrence of a pre-defined “trigger” event, such as a hurricane or an earthquake of a specific magnitude. For some event-linked bonds, the trigger event’s magnitude may be based on losses to a company or industry, industry indexes or readings of scientific instruments rather than specified actual losses. If a trigger event, as defined within the terms of an event-linked bond, involves losses or other metrics exceeding a specific magnitude in the geographic region and time period specified therein, the fund may lose a portion or all of its accrued interest and/or principal invested in such event-linked bond. The fund is entitled to receive principal and interest payments so long as no trigger event occurs of the description and magnitude specified by the instrument.

Event-linked bonds may be issued by government agencies, insurance companies, reinsurers, special purpose corporations or other on-shore or off-shore entities.

Event-linked bonds are typically rated by at least one nationally recognized statistical rating agency, but also may be unrated. The rating for an event-linked bond primarily reflects the rating agency’s calculated probability that a pre-defined trigger event will occur. This rating also assesses the event-linked bond’s credit risk and the model used to calculate the probability of a trigger event.

The fund may invest in inverse floating rate obligations (a type of derivative instrument). The interest rate on inverse floating rate obligations will generally decrease as short-term interest rates increase, and increase as short-term rates decrease. Due to their leveraged structure, the sensitivity of the market value of an inverse floating rate obligation to changes in interest rates is generally greater than a comparable long-term bond issued by the same issuer and with similar credit quality, redemption and maturity provisions. Inverse floating rate obligations may be volatile and involve leverage risk.

The fund may, but is not required to, use futures and options on securities, indices and currencies, forward foreign currency exchange contracts, swaps and other derivatives. A derivative is a security or instrument whose value is determined by reference to the value or the change in value of one or more securities, currencies, indices or other financial instruments. The fund may use derivatives for a variety of purposes, including:

The fund may enter into credit default swaps, which can be used to transfer the credit risk of a security without buying or selling the security.

Normally, the fund invests substantially all of its assets to meet its investment objectives. The fund may invest the remainder of its assets in securities with remaining maturities of less than one year or cash equivalents, or may hold cash. For temporary defensive purposes, including during periods of unusual cash flows, the fund may depart from its principal investment strategies and invest part or all of its assets in these securities or may hold cash. The fund may adopt a defensive strategy when Pioneer believes securities in which the fund normally invests have special or unusual risks or are less attractive due to adverse market, economic, political or other conditions.

In addition to the principal investment strategies discussed above, the fund also may use other techniques, including the following non-principal investment strategies.

The fund may invest in zero coupon securities. Zero coupon securities are debt instruments that do not pay interest during the life of the security but are issued at a discount from the amount the investor will receive when the issuer repays the amount borrowed (the face value). The discount approximates the total amount of interest that would be paid at an assumed interest rate.

The fund may enter into reverse repurchase agreements pursuant to which the fund transfers securities to a counterparty in return for cash, and the fund agrees to repurchase the securities at a later date and for a higher price. Reverse repurchase agreements are treated as borrowings by the fund, are a form of leverage and may make the value of an investment in the fund more volatile and increase the risks of investing in the fund. The fund also may borrow money from banks or other lenders for temporary purposes. The fund may borrow up to 33¹/3% of its total assets. Entering into reverse repurchase agreements and other borrowing transactions may cause the fund to liquidate positions when it may not be advantageous to do so in order to satisfy its obligations or meet segregation requirements.

The fund may lend securities in its portfolio to certain broker-dealers or other institutional investors under agreements which require that the loans be secured continuously by collateral, typically cash, which the fund will invest during the term of the loan. The fund will continue to have market risk and

other risks associated with owning the securities on loan, as well as the risks associated with the investment of the cash collateral received in connection with the loan. The fund may pay a portion of the income earned on the investment of cash collateral to the borrowers of the securities, lending agent or other intermediary. Securities lending also is subject to the risk that the borrower fails to return a loaned security, and/or there is a shortfall on the collateral to be returned to the borrower, and the risk that the fund is unable to recall the security in time to exercise voting rights or sell the security. The fund may lend up to 33¹/3% of its total assets. Any income realized through securities lending may help fund performance.

The fund usually does not trade for short-term profits. The fund will sell an investment, however, even if it has only been held for a short time, if it no longer meets the fund’s investment criteria. If the fund does a lot of trading, it may incur additional operating expenses, which would reduce performance, and could cause shareowners to incur a higher level of taxable income or capital gains.

You could lose money on your investment in the fund. As with any mutual fund, there is no guarantee that the fund will achieve its objective. Following is a description of principal risks of investing in the fund.

High yield or “junk” bond risk. Debt securities that are below investment grade, called “junk bonds,” are speculative, have a higher risk of default or are already in default, tend to be less liquid and are more difficult to value than higher grade securities. Junk bonds tend to be volatile and more susceptible to adverse events and negative sentiments.

Interest rate risk. When interest rates rise, the value of fixed income securities generally falls. A change in interest rates will not have the same impact on all fixed income securities. Generally, the longer the maturity or duration of a fixed income security, the greater the impact of a rise in interest rates on the security’s value. In addition, different interest rate measures (such as short- and long-term interest rates and U.S. and foreign interest rates), or interest rates on different types of securities or securities of different issuers, may not necessarily change in the same amount or in the same direction.

Certain fixed income securities pay interest at variable or floating rates. Variable rate securities tend to reset at specified intervals, while floating rate securities may reset whenever there is a change in a specified index rate. In most cases, these reset provisions reduce the impact of changes in market interest rates on the value of the security. However, some securities do not track the underlying index directly, but reset based on formulas that may produce a leveraging effect; others may also provide for interest payments that vary inversely with market rates. The market prices of these securities may fluctuate significantly when interest rates change.

The values of securities with floating interest rates generally are less sensitive to interest rate changes but may decline in value if their interest rates do not rise as much, or as quickly, as prevailing interest rates. Further, in the case of some instruments, if the underlying reference interest rate does not move by at least a prescribed increment, no adjustment will occur in the floating rate instrument’s interest rate. This means that, when prevailing interest rates increase, a corresponding increase in the instrument’s interest rate may not result and the instrument may decline in value. Unlike fixed rate securities, floating rate securities generally will not increase in value if interest rates decline. Changes in interest rates also will affect the amount of interest income the fund earns on its floating rate investments. Unlike fixed rate securities, when prevailing interest rates decrease, the interest rate payable on floating rate investments will decrease.

Credit risk. If an issuer or guarantor of a security held by the fund or a counterparty to a financial contract with the fund defaults on its obligation to pay principal and/or interest, has its credit rating downgraded or is perceived to be less creditworthy, or the credit quality or value of any underlying assets declines, the value of your investment will decline. In addition, the fund may incur expenses to protect the fund’s interest in securities experiencing these events. Credit risk is broadly gauged by the credit ratings of the securities in which the fund invests. However, ratings are only the opinions of the companies issuing them and are not guarantees as to quality.

Prepayment or call risk. Many fixed income securities give the issuer the option to repay or call the security prior to its maturity date. Issuers often exercise this right when interest rates fall. Accordingly, if the fund holds a fixed income security that can be repaid or called prior to its maturity date, it may not benefit fully from the increase in value that other fixed income securities generally experience when interest rates fall. Upon prepayment of the security, the fund also would be forced to reinvest the proceeds at then current yields, which would be lower than the yield of the security that was repaid or called. In addition, if the fund purchases a fixed income security at a premium (at a price that exceeds its stated par or principal value), the fund may lose the amount of the premium paid in the event of prepayment.

Liquidity risk. Liquidity risk exists when particular investments are difficult to sell. Although most of the fund’s securities must be liquid at the time of investment, securities may become illiquid after purchase by the fund, particularly during periods of market turmoil. When the fund holds illiquid investments, its portfolio may be harder to value, especially in changing markets. If the fund is forced to sell these investments to meet redemptions or for other cash needs, the fund may suffer a loss. In addition, when there is illiquidity in the market for certain securities, the fund, due to limitations on investments in illiquid securities, may be unable to achieve its desired level of exposure to a certain sector. To the extent the fund holds a material percentage of the outstanding debt securities of an issuer, this practice may impact adversely the liquidity and market value of those investments.

Risks of investing in floating rate loans. Floating rate loans and similar investments may be illiquid or less liquid than other investments. No active trading market may exist for many floating rate loans, and many loans are subject to restrictions on resale. Market quotations for these securities may be volatile and/or subject to large spreads between bid and ask prices. Any secondary market may be subject to irregular trading activity and extended trade settlement periods.

When the fund invests in a loan participation, the fund does not have a direct claim against the borrower and must rely upon an intermediate participant to enforce any rights against the borrower. As a result, the fund is subject to the risk that an intermediate participant between the fund and the borrower will fail to meet its obligations to the fund, in addition to the risk that the issuer of the loan will default on its obligations.

Although the features of senior loans, including being secured by collateral and having priority over other obligations of the issuer, reduce some of the risks of investment in below investment grade securities, the loans are subject to significant risks. Pioneer believes, based on its experience, that senior floating rate loans generally have more favorable loss recovery rates than most other types of below investment grade obligations. However, there can be no assurance that the fund’s actual loss recovery experience will be consistent with Pioneer’s prior experience or that the senior loans in which the fund invests will achieve any specific loss recovery rate.

Certain floating rate loans and other corporate debt securities involve refinancings, recapitalizations, mergers and acquisitions, and other financings for general corporate purposes. Other loans are incurred in restructuring or “work-out” scenarios, including debtor-in-possession facilities in bankruptcy. Loans in restructuring or similar scenarios may be especially vulnerable to the inherent uncertainties in restructuring processes. In addition, the highly leveraged capital structure of the borrowers in any of these transactions, whether acquisition financing or restructuring, may make the loans especially vulnerable to adverse economic or market conditions and the risk of default.

Risk of insufficient collateral. The value of collateral, if any, securing a floating rate loan can decline, and may be insufficient to meet the issuer’s obligations or may be difficult to liquidate. In addition, the fund’s access to collateral may be limited by bankruptcy or other insolvency laws. These laws may be less developed and more cumbersome with respect to the fund’s non-U.S. floating rate investments. Floating rate loans may not be fully collateralized. To the extent that a loan is collateralized by stock of the borrower or its affiliates, this stock may lose all or substantially all of its value in the event of bankruptcy of the borrower. Loans that are obligations of a holding company are subject to the risk that, in a bankruptcy of a subsidiary operating company, creditors of the subsidiary may recover from the subsidiary’s assets before the lenders to the holding company would receive any amount on account of the holding company’s interest in the subsidiary.

Risk of disadvantaged access to confidential information. The issuer of a floating rate loan may offer to provide material, non-public information about the issuer to investors, such as the fund. Normally, Pioneer will seek to avoid receiving this type of information about the issuer of a loan either held by, or considered for investment by, the fund. Pioneer’s decision not to receive the information may place it at a disadvantage, relative to other loan investors, in assessing a loan or the loan’s issuer. For example, in instances where holders of floating rate loans are asked to grant amendments, waivers or consents, Pioneer’s inability to assess the impact of these actions may adversely affect the value of the fund’s portfolio. For this and other reasons, it is possible that Pioneer’s decision not to receive material, non-public information under normal circumstances could adversely affect the fund’s investment performance.

Risks of subordinated securities. A holder of securities that are subordinated or “junior” to more senior securities of an issuer is entitled to payment after holders or more senior securities of the issuer. Subordinated securities are more likely to suffer a credit loss than non-subordinated securities of the same issuer, any loss incurred by the subordinated securities is likely to be proportionately greater, and any recovery of interest or principal may take more time. As a result, even a perceived decline in creditworthiness of the issuer is likely to have a greater impact on them.

U.S. government agency obligations risk. The fund invests in obligations issued by agencies and instrumentalities of the U.S. government. Government sponsored entities such as Fannie Mae, Freddie Mac and the Federal Home Loan Banks (FHLBs), although chartered or sponsored by Congress, are not funded by congressional appropriations and the debt and mortgage-backed securities issued by them are neither guaranteed nor issued by the U.S. government. Although the U.S. government has provided financial support to Fannie Mae and Freddie Mac in the past, there can be no assurance that it will support these or other government sponsored entities in the future.

Mortgage-related and asset-backed securities risk. The repayment of certain mortgage-backed and asset-backed securities depends primarily on the cash collections received from the issuer’s underlying asset portfolio and, in certain cases, the issuer’s ability to issue replacement securities. As a result, there could be losses to the fund in the event of credit or market value deterioration in the issuer’s underlying portfolio, mismatches in the timing of the cash flows of the underlying asset interests and the repayment obligations of maturing securities, or the issuer’s inability to issue new or replacement securities. Upon the occurrence of certain triggering events or defaults, the fund may become the holder of underlying assets at a time when those assets may be difficult to sell or may be sold only at a loss. In the event of a default, the value of the underlying collateral may be insufficient to pay certain expenses, such as litigation and foreclosure expenses, and inadequate to pay any principal or unpaid interest. Privately issued mortgage-backed and asset-backed securities are not traded on an exchange and may have a limited market. Without an active trading market, these securities may be particularly difficult to value given the complexities in valuing the underlying collateral.

Certain mortgage-backed and asset-backed securities may pay principal only at maturity or may represent only the right to receive payments of principal or interest on the underlying obligations, but not both. The value of these types of instruments may change more drastically than debt securities that pay both principal and interest during periods of changing interest rates. Principal only instruments generally increase in value if interest rates decline, but are also subject to the risk of prepayment. Interest only instruments generally increase in value in a rising interest rate environment when fewer of the underlying obligations are prepaid. Interest only instruments could lose their entire value in a declining interest rate environment if the underlying obligations are prepaid.

These securities may include instruments that allow for balloon payments or negative amortization payments. Such instruments permit the borrower to avoid paying currently a portion of the interest accruing on the instrument. While these features make the debt instrument more affordable to the borrower in the near term, they increase the risk that the borrower will be unable to make the resulting higher payment or payments that become due at the maturity of the loan.

Unlike mortgage-related securities issued or guaranteed by the U. S. government or its agencies and instrumentalities, mortgage-related securities issued by private issuers do not have a government or government-sponsored entity guarantee (but may have other credit enhancement), and may, and frequently do, have less favorable collateral, credit risk or other characteristics. The fund may invest in other mortgage-related securities, including mortgage derivatives and structured securities. These securities typically are not secured by real property. Because these securities have imbedded leverage features, small changes in interest or prepayment rates may cause large and sudden price movements. These securities also can become illiquid and difficult to value in volatile or declining markets.

The fund may invest in CMOs. If there are defaults on the underlying mortgage loans, the fund will be less likely to receive payments of principal and interest, and will be more likely to suffer a loss. This risk may be increased to the extent the underlying mortgages include sub-prime mortgages.

The fund may invest in CDOs. The risks of an investment in a CDO depend largely on the type of the underlying obligations (e.g., an underlying obligation may decline in quality or default) and the tranche of the CDO in which the fund invests (e.g., the fund may invest in a tranche of CDO that is subordinate to other tranches). Investments in CDOs may be characterized by the fund as illiquid securities, which may be hard to value and difficult to sell at an advantageous time or price. Although certain CDOs may receive credit enhancement in the form of a senior-subordinate structure, over-collateralization or bond insurance, such enhancement may not always be present, and may fail to protect a fund against the risk of loss on default of the collateral.

Risks of investing in event-linked bonds. The return of principal and the payment of interest on “event-linked” bonds are contingent on the non-occurrence of a pre-defined “trigger” event, such as a hurricane or an earthquake of a specific magnitude. If a trigger event, as defined within the terms of an event-linked bond, involves losses or other metrics exceeding a specific magnitude in the geographic region and time period specified therein, the fund may lose a portion or all of its accrued interest and/or principal invested in such event-linked bond. In addition to the specified trigger events, event-linked bonds may expose the fund to other risks, including but not limited to issuer (credit) default, adverse regulatory or jurisdictional interpretations and adverse tax consequences. Event-linked bonds are also subject to the risk that the model used to calculate the probability of a trigger event was not accurate and underestimated the likelihood of a trigger event. Upon the occurrence or possible occurrence of a trigger event, and until the completion of the processing and auditing of applicable loss claims, the fund’s investment in an event-linked bond may be priced using fair value methods. As a relatively new type of financial instrument, there is limited trading history for these securities, and there can be no assurance that a liquid market in these instruments will develop.

Derivatives risk. Using derivatives exposes the fund to additional risks and may increase the volatility of the fund’s net asset value and may not provide the expected result. Derivatives may have a leveraging effect on the fund’s portfolio, and they can disproportionately increase losses and reduce opportunities for gain. If changes in a derivative’s value do not correspond to changes in the value of the fund’s other investments or do not correlate well with the underlying assets, rate or index, the fund may not fully benefit from, or could lose money on, or could experience unusually high expenses as a result of, the derivative position. Derivatives involve the risk of loss if the counterparty defaults on its obligation. Certain derivatives may be less liquid, which may reduce the returns of the fund if it cannot sell or terminate the derivative at an advantageous time or price. The fund also may have to sell assets at inopportune times to satisfy its obligations. Some derivatives may involve the risk of improper valuation. Suitable derivatives may not be available in all circumstances or at reasonable prices and may not be used by the fund for a variety of reasons. Recent legislation calls for new regulation of the derivatives markets. The extent and impact of the regulation is not yet known and may not be known for some time. New regulation of derivatives may make them more costly, may limit their availability, or may otherwise adversely affect their value or performance. Risks associated with the use of derivatives are magnified to the extent that a large portion of the fund’s assets are committed to derivatives in general or are invested in just one or a few types of derivatives.

difficulties in trading and valuation, especially in the event of market disruptions. Recent legislation, noted above, will require most swaps to be executed through a centralized exchange or regulated facility and be cleared through a regulated clearinghouse. The swap market could be disrupted or limited as a result of this legislation, which could adversely affect the fund. Moreover, the establishment of a centralized exchange or market for swap transactions may not result in swaps being easier to trade or value.

Risks of zero coupon bonds and payment in kind securities. Zero coupon bonds (which do not pay interest until maturity) and payment in kind securities (which pay interest in the form of additional securities) may be more speculative and may fluctuate more in value than securities which pay income periodically and in cash. In addition, although the fund receives no periodic cash payments from such investments, applicable tax rules require the fund to accrue and pay out its income from such securities annually as income dividends. Such distributions may be taxable to shareholders and, in addition, could reduce the fund’s reserve position and require the fund to sell securities and incur a gain or loss at a time it may not otherwise want in order to provide the cash necessary for these distributions.

Portfolio selection risk. The adviser’s judgment about a particular security or issuer, or about the economy or a particular sector, region or market segment, or about an investment strategy, may prove to be incorrect.

Market segment risk. To the extent the fund emphasizes, from time to time, investments in a market segment, the fund will be subject to a greater degree to the risks particular to the industries in that segment, and may experience greater market fluctuation, than a fund without the same focus. For example, industries in the financial segment, such as banks, insurance companies, broker-dealers and real estate investment trusts (REITs), may be sensitive to changes in interest rates and general economic activity and are generally subject to extensive government regulation.

Risk of increase in expenses. Your actual costs of investing in the fund may be higher than the expenses shown in “Annual fund operating expenses” for a variety of reasons. For example, expense ratios may be higher than those shown if overall net assets decrease. Net assets are more likely to decrease and fund expense ratios are more likely to increase when markets are volatile.

To learn more about the fund’s investments and risks, you should obtain and read the statement of additional information. Please note that there are many other factors that could adversely affect your investment and that could prevent the fund from achieving its goals.

The fund’s policies and procedures with respect to disclosure of the fund’s portfolio securities are described in the statement of additional information.

Pioneer, the fund’s investment adviser, selects the fund’s investments and oversees the fund’s operations.

Pioneer is an indirect, wholly owned subsidiary of UniCredit S.p.A., one of the largest banking groups in Italy. Pioneer is part of the global asset management group providing investment management and financial services to mutual funds, institutional and other clients. As of March 31, 2011, assets under management were approximately $258 billion worldwide, including over $67 billion in assets under management by Pioneer (and its U.S. affiliates).

The firm’s U.S. mutual fund investment history includes creating in 1928 one of the first mutual funds.

Pioneer has received an order from the Securities and Exchange Commission that permits Pioneer, subject to the approval of the fund’s Board of Trustees, to hire and terminate a subadviser that is not affiliated with Pioneer (an “unaffiliated subadviser”) or to materially modify an existing subadvisory contract with an unaffiliated subadviser for the fund without shareholder approval. Pioneer retains the ultimate responsibility to oversee and recommend the hiring, termination and replacement of any unaffiliated subadviser. To the extent that the Securities and Exchange Commission adopts a rule that would supersede the order, or would provide greater flexibility than the order, Pioneer and the fund intend to rely on such rule to permit Pioneer, subject to the approval of the fund’s Board of Trustees and any other applicable conditions of the rule, to hire and terminate an unaffiliated subadviser or to materially modify an existing subadvisory contract with an unaffiliated subadviser for the fund without shareholder approval.

Day-to-day management of the fund’s portfolio is the responsibility of Charles Melchreit, Seth Roman and Jonathan Sharkey. The portfolio managers are supported by the fixed income team. Members of this team manage other Pioneer funds investing primarily in fixed income securities. The portfolio managers and the team also may draw upon the research and investment management expertise of Pioneer’s affiliate, Pioneer Investment Management Limited. Mr. Melchreit, Portfolio Manager and a Vice President of Pioneer, joined Pioneer in 2006. From 2003 to 2004, Mr. Melchreit was a managing director at Cigna Investment Management. Prior to that, he was senior vice president and portfolio manager at Aeltus Management. Mr. Melchreit received an MS degree in Statistics from Yale University in 2005. Mr. Melchreit has served as a portfolio manager of the fund since 2011. Mr. Roman, Portfolio Manager and a Vice President of Pioneer, joined Pioneer in 2006. Prior to joining Pioneer, Mr. Roman was a fixed income trader for Fidelity Management and Research Company. Mr. Roman has served as a portfolio manager of the fund since 2011. Mr. Sharkey, Portfolio Manager and a Vice President of Pioneer, joined Pioneer in August 2006. From March 2004

to August 2006, Mr. Sharkey was employed by Putnam Investments as a corporate bond and leveraged loan analyst. Prior to that, he was a principal and leveraged loan analyst at Cypress Tree Investments. Mr. Sharkey has served as a portfolio manager of the fund since 2011.

The fund’s statement of additional information provides additional information about the portfolio managers’ compensation, other accounts managed by the portfolio managers, and the portfolio managers’ ownership of shares of the fund.

The fund pays Pioneer a fee for managing the fund and to cover the cost of providing certain services to the fund. Pioneer’s annual fee is equal to 0.35% of the fund’s average daily net assets up to $1 billion and 0.30% on assets over $1 billion. The fee is accrued daily and paid monthly.

A discussion regarding the basis for the Board of Trustees’ approval of the management contract is available in the fund’s semiannual report to shareholders, for the period ended September 30, 2011.

Pioneer Funds Distributor, Inc. is the fund’s distributor. Pioneer Investment Management Shareholder Services, Inc. is the fund’s transfer agent. The fund compensates the distributor and transfer agent for their services. The distributor and the transfer agent are affiliates of Pioneer.

The fund’s net asset value is the value of its securities plus any other assets minus its accrued operating expenses and other liabilities. The fund calculates a net asset value for each class of shares every day the New York Stock Exchange is open when regular trading closes (normally 4:00 p.m. Eastern time). If the New York Stock Exchange closes at another time, the fund will calculate a net asset value for each class of shares as of the actual closing time.

The fund generally values debt securities and certain derivative instruments by using the prices supplied by independent third party pricing services. A pricing service may use market prices or quotations from one or more brokers or other sources, or may use a pricing matrix or other fair value methods or techniques to provide an estimated value of the security or instrument. A pricing matrix is a means of valuing a debt security on the basis of current market prices for other debt securities, historical trading patters in the market for fixed income securities and/or other factors. Non-U.S. debt securities that are listed on an exchange will be valued at the bid price obtained from an independent third party pricing service.

Senior loans are valued at the mean between the last available bid and asked prices for one or more brokers or dealers as obtained from an independent third party pricing service. Senior loans for which no reliable price quotes are available, will be valued by an independent third party pricing service through the use of a pricing matrix or other fair value methods or techniques. Event linked bonds are valued at the bid price obtained from an independent third party pricing service.

The fund values short-term fixed income securities with remaining maturities of 60 days or less at amortized cost, unless circumstances indicate that using this method would not reflect an investment’s value.

The fund generally values its equity securities and certain derivative instruments that are traded on an exchange using the last sale price on the principal exchange on which they are traded. Equity securities that are not traded on the date of valuation, or securities for which no last sale prices are available, are valued at the mean between the last bid and asked prices or, if both last bid and asked prices are not available, at the last quoted bid price. Last sale, bid and asked prices are provided by independent third party pricing services. In the case of equity securities not traded on an exchange, prices are typically determined by independent third party pricing services approved by the Board of Trustees using a variety of techniques and methods. The fund may use a fair value model developed by an independent pricing service to value non-U.S. equity securities.

To the extent that the fund invests in shares of other mutual funds that are not traded on an exchange, such shares are valued at their net asset values as provided by those funds. The prospectuses for those funds explain the

circumstances under which those funds will use fair value pricing methods and the effects of using fair value pricing methods.

The valuations of securities traded in non-U.S. markets and certain fixed income securities will generally be determined as of the earlier closing time of the markets on which they primarily trade. When the fund holds securities or other assets that are denominated in a foreign currency, the fund will normally use the currency exchange rates as of 3:00 p.m. (Eastern time). Non-U.S. markets are open for trading on weekends and other days when the fund does not price its shares. Therefore, the value of the fund’s shares may change on days when you will not be able to purchase or redeem fund shares.

When independent third party pricing services are unable to supply prices for an investment, or when prices or market quotations are considered by Pioneer to be unreliable, the value of that security may be determined using quotations from one or more broker-dealers. When such prices or quotations are not available, or when they are considered by Pioneer to be unreliable, the fund uses fair value methods to value its securities pursuant to procedures adopted by the Board of Trustees. The fund also may use fair value methods if it is determined that a significant event has occurred between the time at which a price is determined and the time at which the fund’s net asset value is calculated. Because the fund may invest in securities rated below investment grade — some of which may be thinly-traded and for which prices may not be readily available or may be unreliable — the fund may use fair value methods more frequently than funds that primarily invest in securities that are more widely traded. Valuing securities using fair value methods may cause the net asset value of the fund’s shares to differ from the net asset value that would be calculated only using market prices.

The prices used by the fund to value its securities may differ from the amounts that would be realized if these securities were sold and these differences may be significant, particularly for securities that trade in relatively thin markets and/or markets that experience extreme volatility.

The fund offers three classes of shares through this prospectus. Each class has different eligibility requirements, sales charges and expenses, allowing you to choose the class that best meets your needs.

Your investment professional can help you determine which class meets your goals. Your investment professional or financial intermediary may receive different compensation depending upon which class you choose. If you are not a U.S. citizen and are purchasing shares outside the U.S., you may pay different sales charges under local laws and business practices.

The fund has adopted a distribution plan for Class A and Class C shares in accordance with Rule 12b-1 under the Investment Company Act of 1940. Under the plan, the fund pays distribution and service fees to the distributor. Because these fees are an ongoing expense of the fund, over time they increase the cost of your investment and your shares may cost more than shares that are subject to other types of sales charges.

Your financial intermediary may receive compensation from the fund, Pioneer and its affiliates for the sale of fund shares and related services. Compensation may include sales commissions and distribution and service (Rule 12b-1) fees, as well as compensation for administrative services and transaction processing.

Pioneer and its affiliates may make additional payments to your financial intermediary. These payments may provide your financial intermediary with an incentive to favor the Pioneer funds over other mutual funds or assist the distributor in its efforts to promote the sale of the fund’s shares. Financial intermediaries include broker-dealers, banks (including bank trust departments), registered investment advisers, financial planners, retirement plan administrators and other types of intermediaries.

Pioneer makes these additional payments (sometimes referred to as “revenue sharing”) to financial intermediaries out of its own assets, which may include profits derived from services provided to the fund, or from the retention of a portion of sales charges or distribution and service fees. Pioneer may base these payments on a variety of criteria, including the amount of sales or assets of the Pioneer funds attributable to the financial intermediary or as a per transaction fee.

Not all financial intermediaries receive additional compensation and the amount of compensation paid varies for each financial intermediary. In certain cases, these payments may be significant. Pioneer determines which firms to support and the extent of the payments it is willing to make, generally choosing firms that have a strong capability to effectively distribute shares of the Pioneer funds and that are willing to cooperate with Pioneer’s promotional efforts. Pioneer also may compensate financial intermediaries (in addition to amounts that may be paid by the fund) for providing certain administrative services and transaction processing services.

Pioneer may benefit from revenue sharing if the intermediary features the Pioneer funds in its sales system (such as by placing certain Pioneer funds on its preferred fund list or giving access on a preferential basis to members of the financial intermediary’s sales force or management). In addition, the financial intermediary may agree to participate in the distributor’s marketing efforts (such as by helping to facilitate or provide financial assistance for conferences, seminars or other programs at which Pioneer personnel may make presentations on the Pioneer funds to the intermediary’s sales force).

To the extent intermediaries sell more shares of the Pioneer funds or retain shares of the Pioneer funds in their clients’ accounts, Pioneer receives greater management and other fees due to the increase in the Pioneer funds’ assets. The intermediary may earn a profit on these payments if the amount of the payment to the intermediary exceeds the intermediary’s costs.

The compensation that Pioneer pays to financial intermediaries is discussed in more detail in the fund’s statement of additional information. Your intermediary may charge you additional fees or commissions other than those disclosed in this prospectus. Intermediaries may categorize and disclose these arrangements differently than in the discussion above and in the statement of additional information. You can ask your financial intermediary about any payments it receives from Pioneer or the Pioneer funds, as well as about fees and/or commissions it charges.

Pioneer and its affiliates may have other relationships with your financial intermediary relating to the provision of services to the Pioneer funds, such as providing omnibus account services or effecting portfolio transactions for the Pioneer funds. If your intermediary provides these services, Pioneer or the Pioneer funds may compensate the intermediary for these services. In addition, your intermediary may have other relationships with Pioneer or its affiliates that are not related to the Pioneer funds.

You pay the offering price (the net asset value per share plus any initial sales charge) when you buy Class A shares unless you qualify to purchase shares at net asset value. You pay a lower sales charge as the size of your investment increases. You do not pay a sales charge when you reinvest dividends or capital gain distributions paid by the fund.

The dollar amount of the sales charge is the difference between the offering price of the shares purchased (based on the applicable sales charge in the table) and the net asset value of those shares. Since the offering price is calculated to two decimal places using standard rounding methodology, the dollar amount of the sales charge as a percentage of the offering price and of the net amount invested for any particular purchase of fund shares may be higher or lower due to rounding.

You may qualify for a reduced Class A sales charge if you own or are purchasing shares of Pioneer mutual funds. The investment levels required to obtain a reduced sales charge are commonly referred to as “breakpoints.” Pioneer offers two principal means of taking advantage of breakpoints in sales charges for aggregate purchases of Class A shares of the Pioneer funds over time if:

If you qualify for rights of accumulation, your sales charge will be based on the combined value (at the current offering price) of all your Pioneer mutual fund shares, the shares of your spouse and the shares of any children under the age of 21.

You can use a letter of intent to qualify for reduced sales charges in two situations:

Completing a letter of intent does not obligate you to purchase additional shares, but if you do not buy enough shares to qualify for the projected level of sales charges by the end of the 13-month period (or when you sell your shares, if earlier), the distributor will recalculate your sales charge. You must pay the additional sales charge within 20 days after you are notified of the recalculation or it will be deducted from your account (or your sale proceeds). Any share class for which no sales charge is paid cannot be included under the letter of intent. For more information regarding letters of intent, please contact your investment professional or obtain and read the statement of additional information.

In calculating your total account value in order to determine whether you have net sales charge breakpoints, you can include your Pioneer mutual fund shares, those of your spouse and the shares of any children under the age of 21. Pioneer will use each fund’s current offering price to calculate your total account value. Certain trustees and fiduciaries may also qualify for a reduced sales charge.

To receive a reduced sales charge, you or your investment professional must, at the time of purchase, notify the distributor of your eligibility. In order to verify your eligibility for a discount, you may need to provide your investment professional or the fund with information or records, such as account numbers or statements, regarding shares of the fund or other Pioneer mutual funds held in all accounts by you, your spouse or children under the age of 21 with that investment professional or with any other financial intermediary. Eligible accounts may include joint accounts, retirement plan accounts, such as IRA and 401k accounts, and custodial accounts, such as ESA, UGMA and UTMA accounts.

It is your responsibility to confirm that your investment professional has notified the distributor of your eligibility for a reduced sales charge at the time of sale. If you or your investment professional do not notify the distributor of your eligibility, you will risk losing the benefits of a reduced sales charge.

For this purpose, Pioneer mutual funds include any fund for which the distributor is principal underwriter and, at the distributor’s discretion, may include funds organized outside the U.S. and managed by Pioneer or an affiliate.

You can locate information regarding the reduction or waiver of sales charges, in a clear and prominent format and free of charge, on Pioneer’s website at www.pioneerinvestments.com. The website includes hyperlinks that facilitate access to this information.

Class A purchases at a reduced initial sales charge or net asset value are also available to:

You may purchase Class A shares at net asset value (without a sales charge) as follows. If you believe you qualify for any of the Class A sales charge waivers discussed below, contact your investment professional or the distributor. You are required to provide written confirmation of your eligibility. You may not resell these shares except to or on behalf of the fund.

You do not pay a sales charge when you purchase Class A shares if you are investing $500,000 or more, are a participant in an employer-sponsored retirement plan with at least $500,000 in total plan assets or are a participant in certain employer-sponsored retirement plans with accounts established with Pioneer on or before March 31, 2004 with 100 or more eligible employees or at least $500,000 in total plan assets. However, you may pay a contingent deferred sales charge if you sell your Class A shares within 12 months of purchase. The sales charge is equal to 1% of your investment or your sale proceeds, whichever is less.

In addition, Class A shares may be purchased at net asset value through certain mutual fund programs sponsored by qualified intermediaries, such as broker-dealers and investment advisers. In each case, the intermediary has entered into an agreement with Pioneer to include the Pioneer funds in their program without the imposition of a sales charge. The intermediary provides investors participating in the program with additional services, including advisory, asset allocation, recordkeeping or other services. You should ask your investment firm if it offers and you are eligible to participate in such a

mutual fund program and whether participation in the program is consistent with your investment goals. The intermediaries sponsoring or participating in these mutual fund programs also may offer their clients other classes of shares of the funds and investors may receive different levels of services or pay different fees depending upon the class of shares included in the program. Investors should consider carefully any separate transaction and other fees charged by these programs in connection with investing in each available share class before selecting a share class.

Purchases of Class A shares of $500,000 or more, or by participants in a group plan which were not subject to an initial sales charge, may be subject to a contingent deferred sales charge upon redemption. A contingent deferred sales charge is payable to the distributor in the event of a share redemption within 12 months following the share purchase at the rate of 1% of the lesser of the value of the shares redeemed (exclusive of reinvested dividend and capital gain distributions) or the total cost of such shares. However, the contingent deferred sales charge is waived for redemptions of Class A shares purchased by an employer-sponsored retirement plan that has at least $500,000 in total plan assets (or that has 1,000 or more eligible employees for plans with accounts established with Pioneer on or before March 31, 2004).

You buy Class C shares at net asset value per share without paying an initial sales charge. However, if you sell your Class C shares within one year of purchase, upon redemption you will pay the distributor a contingent deferred sales charge of 1% of the current market value or the original cost of the shares you are selling, whichever is less.

Several rules apply for calculating CDSCs so that you pay the lowest possible CDSC.

It is your responsibility to confirm that your investment professional has notified the distributor of your eligibility for a reduced sales charge at the time

of sale. If you or your investment professional do not notify the distributor of your eligibility, you will risk losing the benefits of a reduced sales charge.

The distributor may waive or reduce the CDSC for Class A shares that are subject to a CDSC or for Class C shares if:

Please see the fund’s statement of additional information for more information regarding reduced sales charges and breakpoints.

You may open an account by completing an account application and sending it to the transfer agent by mail or by fax. Please call the transfer agent to obtain an account application. Certain types of accounts, such as retirement accounts, have separate applications.

Use your account application to select options and privileges for your account. You can change your selections at any time by sending a completed account options form to the transfer agent. You may be required to obtain a signature guarantee to make certain changes to an existing account.

Call or write to the transfer agent for account applications, account options forms and other account information:

To help the government fight the funding of terrorism and money laundering activities, federal law requires all financial institutions to obtain, verify and record information that identifies each person who opens an account. When you open an account, you will need to supply your name, address, date of birth, and other information that will allow the fund to identify you.

The fund may close your account if we cannot adequately verify your identity. The redemption price will be the net asset value on the date of redemption.

If you invest in the fund though your financial intermediary or though a retirement plan, the options and services available to you may be different from those discussed in this prospectus. Shareholders investing through financial intermediaries, programs sponsored by financial intermediaries and retirement plans may only purchase funds and classes of shares that are available. When you invest through an account that is not in your name, you generally may buy and sell shares and complete other transactions only though the account. Ask your investment professional or financial intermediary for more information.

Additional conditions may apply to your investment in the fund, and the investment professional or intermediary may charge you a transaction-based, administrative or other fee for its services. These conditions and fees are in addition to those imposed by the fund and its affiliates. You should ask your investment professional or financial intermediary about its services and any applicable fees.

If you place an order to purchase, exchange or sell shares with the transfer agent or an authorized agent by the close of regular trading on the New York Stock Exchange (usually 4:00 p.m. Eastern time), the share price for your transaction will be based on the net asset value determined as of the close of regular trading on the New York Stock Exchange on that day (plus or minus any applicable sales charges). If your order is placed with the transfer agent or an authorized agent after the close of regular trading on the New York Stock Exchange, or your order is not in good order, the share price will be based on the net asset value next determined after your order is received in good order by the fund or authorized agent. The authorized agent is responsible for transmitting your order to the fund in a timely manner.

Good order means that:

•

You have provided adequate instructions

•

There are no outstanding claims against your account

•

There are no transaction limitations on your account

•

If you have any fund share certificates, you submit them and they are signed by each record owner exactly as the shares are registered

•

Your request includes a signature guarantee if you:

–

Are selling over $100,000 or exchanging over $500,000 worth of shares

–

Changed your account registration or address within the last 30 days

–

Instruct the transfer agent to mail the check to an address different from the one on your account

–

Want the check paid to someone other than the account’s record owner(s)

–

Are transferring the sale proceeds to a Pioneer mutual fund account with a different registration

Your transactions are subject to certain limitations, including the limitation on the purchase of the fund’s shares within 30 calendar days of a redemption. See “Excessive trading.”

You may buy fund shares from any financial intermediary that has a sales agreement or other arrangement with the distributor.

You can buy shares at net asset value per share plus any applicable sales charge. The distributor may reject any order until it has confirmed the order in writing and received payment. Normally, your financial intermediary will send your purchase request to the fund’s transfer agent. Consult your investment professional for more information. Your investment firm receives a commission from the distributor, and may receive additional compensation from Pioneer, for your purchase of fund shares.

Your initial investment must be at least $1,000. Additional investments must be at least $100 for Class A shares and $500 for Class C shares.

You may qualify for lower initial or subsequent investment minimums if you are opening a retirement plan account, establishing an automatic investment plan or placing your trade through your investment firm. The fund may waive the initial or subsequent investment minimums. Minimum investment amounts may be waived for, among other things, share purchases made through certain mutual fund programs (e.g., asset based fee program accounts) sponsored by qualified intermediaries, such as broker-dealers and investment advisers, that have entered into an agreement with Pioneer.

Your initial investment in Class Y shares must be at least $5 million. This amount may be invested in one or more of the Pioneer mutual funds that currently offer Class Y shares. There is no minimum additional investment amount. The fund may waive the initial investment amount.

The fund reserves the right to waive the initial investment minimum in other circumstances.

Purchases of fund shares are limited to $499,999 for Class C shares. This limit is applied on a per transaction basis. Class A shares and Class Y shares are not subject to a maximum purchase amount.

You can purchase fund shares through tax-deferred retirement plans for individuals, businesses and tax-exempt organizations.

Your initial investment for most types of retirement plan accounts must be at least $250. Additional investments for most types of retirement plans must be at least $100.

You may not use the account application accompanying this prospectus to establish a Pioneer retirement plan. You can obtain retirement plan applications from your investment firm or by calling the Retirement Plans Department at 1-800-622-0176.

Normally, your investment firm will send your purchase request to the fund’s distributor and/or transfer agent. Consult your investment professional for more information. Your investment firm receives a commission from the distributor, and may receive additional compensation from Pioneer, for your purchase of fund shares.

You can use the telephone or online purchase privilege if you have an existing non-retirement account. Certain IRAs can use the telephone purchase privilege. If your account is eligible, you can purchase additional fund shares by phone or online if:

When you request a telephone or online purchase, the transfer agent will electronically debit the amount of the purchase from your bank account of record. The transfer agent will purchase fund shares for the amount of the debit at the offering price determined after the transfer agent receives your telephone or online purchase instruction and good funds. It usually takes three business days for the transfer agent to receive notification from your bank that good funds are available in the amount of your investment.

You can purchase fund shares for an existing fund account by mailing a check to the transfer agent. Make your check payable to the fund. Neither initial nor subsequent investments should be made by third party check, travelers check, or credit card check. Your check must be in U.S. dollars and drawn on a U.S. bank. Include in your purchase request the fund’s name, the account number and the name or names in the account registration.

If you have an existing Class Y account, you may wire funds to purchase shares. Note, however, that:

The transfer agent must receive your account application before you send your initial check or federal funds wire. In addition, you must provide a bank wire address of record when you establish your account.

You may, under certain circumstances, exchange your shares for shares of the same class of another Pioneer mutual fund.

Your exchange request must be for at least $1,000. The fund allows you to exchange your shares at net asset value without charging you either an initial or contingent deferred sales charge at the time of the exchange. Shares you acquire as part of an exchange will continue to be subject to any contingent deferred sales charge that applies to the shares you originally purchased. When you ultimately sell your shares, the date of your original purchase will determine your contingent deferred sales charge.

Before you request an exchange, consider each fund’s investment objective and policies as described in the fund’s prospectus. You generally will have to pay income taxes on an exchange.

Same-fund Exchange Privilege. Certain shareholders may be eligible to exchange their shares for the fund’s Class Y shares. If eligible, no sales charges or other charges will apply to any such exchange. Generally, shareholders will not recognize a gain or loss for federal income tax purposes upon such an exchange. Investors should contact their financial intermediary to learn more about the details of this privilege.

Normally, your investment firm will send your exchange request to the fund’s transfer agent. Consult your investment professional for more information about exchanging your shares.

After you establish an eligible fund account, you can exchange fund shares by phone or online if:

You can exchange fund shares by mailing or faxing a letter of instruction to the transfer agent. You can exchange fund shares directly through the fund only if your account is registered in your name. However, you may not fax an exchange request for more than $500,000. Include in your letter:

Your shares will be sold at the share price (net asset value less any applicable sales charge) next calculated after the fund or its authorized agent, such as a broker-dealer, receives your request in good order. If a signature guarantee is required, you must submit your request in writing.

If the shares you are selling are subject to a deferred sales charge, it will be deducted from the sale proceeds. The fund generally will send your sale proceeds by check, bank wire or electronic funds transfer. Normally you will be paid within seven days. If you recently sent a check to purchase the shares being sold, the fund may delay payment of the sale proceeds until your check has cleared. This may take up to 10 calendar days from the purchase date.

If you are selling shares from a non-retirement account or certain IRAs, you may use any of the methods described below. If you are selling shares from a retirement account other than an IRA, you must make your request in writing.

If you must use a written request to exchange or sell your shares and your account is registered in the name of a corporation or other fiduciary you must include the name of an authorized person and a certified copy of a current corporate resolution, certificate of incumbency or similar legal document showing that the named individual is authorized to act on behalf of the record owner.

Normally, your investment firm will send your request to sell shares to the fund’s transfer agent. Consult your investment professional for more information. The fund has authorized the distributor to act as its agent in the

repurchase of fund shares from qualified investment firms. The fund reserves the right to terminate this procedure at any time.

If you have an eligible non-retirement account, you may sell up to $100,000 per account per day by phone or online. You may sell fund shares held in a retirement plan account by phone only if your account is an eligible IRA (tax penalties may apply). You may not sell your shares by phone or online if you have changed your address (for checks) or your bank information (for wires and transfers) in the last 30 days.

For Class Y shares, shareholders may sell up to $5 million per account per day if the proceeds are directed to your bank account of record ($100,000 per account per day if the proceeds are not directed to your bank account of record).

You can sell some or all of your fund shares by writing directly to the fund only if your account is registered in your name. Include in your request your name, the fund’s name, your fund account number, the class of shares to be sold, the dollar amount or number of shares to be sold and any other applicable requirements as described below. The transfer agent will send the sale proceeds to your address of record unless you provide other instructions. Your request must be signed by all registered owners and be in good order.

The transfer agent will not process your request until it is received in good order.

For information or to request a telephone transaction between 8:00 a.m. and 7:00 p.m. (Eastern time) by speaking with a shareholder services representative call

See the account application form for more details on each of the following services or call the transfer agent for details and availability.

If your account is registered in your name, you can buy, exchange or sell fund shares by telephone. If you do not want your account to have telephone transaction privileges, you must indicate that choice on your account application or by writing to the transfer agent.

When you request a telephone transaction the transfer agent will try to confirm that the request is genuine. The transfer agent records the call, requires the caller to provide validating information for the account and sends you a written confirmation. The fund may implement other confirmation procedures from time to time. Different procedures may apply if you have a non-U.S. account or if your account is registered in the name of an institution, broker-dealer or other third party. If the fund’s confirmation procedures are followed, neither the fund nor its agents will bear any liability for these transactions.

If your account is registered in your name, you may be able to buy, exchange or sell fund shares online. Your investment firm may also be able to buy, exchange or sell your fund shares online.

To use online transactions, you must read and agree to the terms of an online transaction agreement available on the Pioneer website. When you or your investment firm requests an online transaction the transfer agent electronically records the transaction, requires an authorizing password and sends a written confirmation. The fund may implement other procedures from time to time. Different procedures may apply if you have a non-U.S. account or if your account is registered in the name of an institution, broker-dealer or other third party. You may not be able to use the online transaction privilege for certain types of accounts, including most retirement accounts.

You can make regular periodic investments in the fund by setting up monthly bank drafts, government allotments, payroll deductions, a Pioneer Investomatic Plan and other similar automatic investment plans. Automatic investments may be made only through U.S. banks. You may use an automatic investment plan to establish a Class A share account with a small initial investment. If you have a Class C or Class R share account and your balance is at least $1,000, you may establish an automatic investment plan.

If you establish a Pioneer Investomatic Plan, the transfer agent will make a periodic investment in fund shares by means of a preauthorized electronic funds transfer from your bank account. Your plan investments are voluntary. You may discontinue your plan at any time or change the plan’s dollar amount, frequency or investment date by calling or writing to the transfer agent. You should allow up to 30 days for the transfer agent to establish your plan.

You can automatically exchange your fund shares for shares of the same class of another Pioneer mutual fund. The automatic exchange will begin on the day you select when you complete the appropriate section of your account application or an account options form. In order to establish automatic exchange:

The fund offers three distribution options. Any fund shares you buy by reinvesting distributions will be priced at the applicable net asset value per share.

Options (2) and (3) are not available to retirement plan accounts or accounts with a current value of less than $500.

If your distribution check is returned to the transfer agent or you do not cash the check for six months or more, the transfer agent may reinvest the amount of the check in your account and automatically change the distribution option on your account to option (1) until you request a different option in writing. If the amount of a distribution check would be less than $10, the fund may reinvest the amount in additional shares of the fund instead of sending a check. Additional shares of the fund will be purchased at the then-current net asset value.

You can invest the dividends paid by one of your Pioneer mutual fund accounts in a second Pioneer mutual fund account. The value of your second account must be at least $1,000. You may direct the investment of any amount of dividends. There are no fees or charges for directed dividends. If you have a retirement plan account, you may only direct dividends to accounts with identical registrations.

When you establish a systematic withdrawal plan for your account, the transfer agent will sell the number of fund shares you specify on a periodic basis and the proceeds will be paid to you or to any person you select. You must obtain a signature guarantee to direct payments to another person after you have established your systematic withdrawal plan. Payments can be made either by check or by electronic transfer to a U.S. bank account you designate.

These requirements do not apply to scheduled (Internal Revenue Code Section 72(t) election) or mandatory (required minimum distribution) withdrawals from IRAs and certain retirement plans.

Systematic sales of fund shares may be taxable transactions for you. While you are making systematic withdrawals from your account, you may pay unnecessary initial sales charges on additional purchases of Class A shares or contingent deferred sales charges.

If you elect to take dividends or dividends and capital gain distributions in cash, or if you establish a systematic withdrawal plan, you may choose to have those cash payments deposited directly into your savings, checking or NOW bank account.

You may have the transfer agent withhold 28% of the dividends and capital gain distributions paid from your fund account (before any reinvestment) and forward the amount withheld to the Internal Revenue Service as a credit against your federal income taxes. Voluntary tax withholding is not available for retirement plan accounts or for accounts subject to backup withholding.

Frequent trading into and out of the fund can disrupt portfolio management strategies, harm fund performance by forcing the fund to hold excess cash or to liquidate certain portfolio securities prematurely and increase expenses for all investors, including long-term investors who do not generate these costs. An investor may use short-term trading as a strategy, for example, if the investor believes that the valuation of the fund’s portfolio securities for purposes of calculating its net asset value does not fully reflect the then-current fair market value of those holdings. The fund discourages, and does not take any intentional action to accommodate, excessive and short-term trading practices, such as market timing. Although there is no generally applied standard in the marketplace as to what level of trading activity is excessive, we may consider trading in the fund’s shares to be excessive for a variety of reasons, such as if:

The fund’s Board of Trustees has adopted policies and procedures with respect to frequent purchases and redemptions of fund shares by fund investors. Pursuant to these policies and procedures, we monitor selected trades on a daily basis in an effort to detect excessive short-term trading. If we determine that an investor or a client of a broker or other intermediary has engaged in excessive short-term trading that we believe may be harmful to the fund, we will ask the investor, broker or other intermediary to cease such activity and we will refuse to process purchase orders (including purchases by exchange) of such investor, broker, other intermediary or accounts that we believe are under their control. In determining whether to take such actions, we seek to act in a manner that is consistent with the best interests of the fund’s shareholders.

While we use our reasonable efforts to detect excessive trading activity, there can be no assurance that our efforts will be successful or that market timers will not employ tactics designed to evade detection. If we are not successful, your return from an investment in the fund may be adversely affected. Frequently, fund shares are held through omnibus accounts maintained by financial intermediaries such as brokers and retirement plan administrators, where the holdings of multiple shareholders, such as all the clients of a particular broker or other intermediary, are aggregated. Our ability to monitor trading practices by investors purchasing shares through omnibus accounts may be limited and dependent upon the cooperation of the broker or other intermediary in taking steps to limit this type of activity.

The fund may reject a purchase or exchange order before its acceptance or the issuance of shares. The fund may also restrict additional purchases or exchanges in an account. Each of these steps may be taken for any transaction, for any reason, without prior notice, including transactions that the fund believes are requested on behalf of market timers. The fund reserves the right to reject any purchase or exchange request by any investor or financial institution if the fund believes that any combination of trading activity in the account or related accounts is potentially disruptive to the fund. A prospective investor whose purchase or exchange order is rejected will not achieve the investment results, whether gain or loss, that would have been realized if the order had been accepted and an investment made in the fund. A fund and its shareholders do not incur any gain or loss as a result of a rejected order. The fund may impose further restrictions on trading activities by market timers in the future.

To limit the negative effects of excessive trading on the fund, the fund has adopted the following restriction on investor transactions. If an investor redeems $5,000 or more (including redemptions that are a part of an exchange transaction) from the fund, that investor shall be prevented (or “blocked”) from purchasing shares of the fund (including purchases that are a part of an exchange transaction) for 30 calendar days after the redemption. This policy does not apply to systematic purchase or withdrawal plan transactions, transactions made through employer-sponsored retirement plans described under Section 401(a), 403(b) or 457 of the Internal Revenue Code or employee benefit plans, scheduled (Internal Revenue Code Section 72(t) election) or mandatory (required minimum distribution) withdrawals from IRAs, rebalancing transactions made through certain asset allocation or “wrap” programs, transactions by insurance company separate accounts or transactions by other funds that invest in the fund. This policy does not apply to purchase or redemption transactions of less than $5,000 or to the Pioneer money market funds.

We rely on financial intermediaries that maintain omnibus accounts to apply to their customers either the fund’s policy described above or their own policies or restrictions designed to limit excessive trading of fund shares. However, we do not impose this policy at the omnibus account level.

Purchases pursuant to the reinstatement privilege (for Class A shares) are subject to this policy.

You may use securities you own to purchase shares of the fund provided that Pioneer, in its sole discretion, determines that the securities are consistent with the fund’s objective and policies and their acquisition is in the best interests of the fund. If the fund accepts your securities, they will be valued for purposes of determining the number of fund shares to be issued to you in the same way the fund will value the securities for purposes of determining its net asset value. For federal income tax purposes, you may be taxed in the

same manner as if you sold the securities that you use to purchase fund shares for cash in an amount equal to the value of the fund shares that you purchase. Your broker may also impose a fee in connection with processing your purchase of fund shares with securities.

If you recently sold all or part of your Class A shares, you may be able to reinvest all or part of your sale proceeds without a sales charge in Class A shares of any Pioneer mutual fund. To qualify for reinstatement:

Purchases pursuant to the reinstatement privilege are subject to limitations on investor transactions, including the limitation on the purchase of the fund’s shares within 30 calendar days of redemption. See “Excessive trading.”

When you elect reinstatement, you are subject to the provisions outlined in the selected fund’s prospectus, including the fund’s minimum investment requirement. Your sale proceeds will be reinvested in shares of the fund at the Class A net asset value per share determined after the transfer agent receives your written request for reinstatement. You may realize a gain or loss for federal income tax purposes as a result of your sale of fund shares, and special tax rules may apply if you elect reinstatement. Consult your tax adviser for more information.

The website includes a full selection of information on mutual fund investing. You can also use the website to get:

If you or your investment firm authorized your account for the online transaction privilege, you may buy, exchange and sell shares online.

If you plan to use FactFone^SM to make telephone purchases and redemptions, first you must activate your personal identification number and establish your bank account of record. If your account is registered in the name of a broker-dealer or other third party, you may not be able to use FactFone^SM.

If your account is registered in the name of a broker-dealer or other third party, you may not be able to use FactFone^SM to obtain account information.

With your consent, Pioneer may send a single proxy statement, prospectus and shareowner report to your residence for you and any other member of your household who has an account with the fund. If you wish to revoke your consent to this practice, you may do so by notifying Pioneer, by phone or in writing (see “How to contact us”). Pioneer will begin mailing separate proxy statements, prospectuses and shareowner reports to you within 30 days after receiving your notice.

The transfer agent maintains an account for each investment firm or individual shareowner and records all account transactions. You will be sent confirmation statements showing the details of your transactions as they occur, except automatic investment plan transactions, which are confirmed quarterly. If you have more than one Pioneer mutual fund account registered in your name, the Pioneer combined account statement will be mailed to you each quarter.

Early each year, the fund will mail you information about the tax status of the dividends and distributions paid to you by the fund.

In January (or by the applicable Internal Revenue Service deadline) following the year in which you take a reportable distribution, the transfer agent will mail you a tax form reflecting the total amount(s) of distribution(s) received by the end of January.

The fund has a policy designed to protect the privacy of your personal information. A copy of Pioneer’s privacy notice was given to you at the time you opened your account. The fund will send you a copy of the privacy notice each year. You may also obtain the privacy notice by calling the transfer agent or through Pioneer’s website.

You can obtain a signature guarantee from most broker-dealers, banks, credit unions (if authorized under state law) and federal savings and loan associations. You cannot obtain a signature guarantee from a notary public.

The Pioneer funds generally accept only medallion signature guarantees. A medallion signature guarantee may be obtained from a domestic bank or trust company, broker, dealer, clearing agency, savings association, or other financial institution that is participating in a medallion program recognized by the Securities Transfer Association. Signature guarantees from financial institutions that are not participating in one of these programs are not accepted as medallion signature guarantees. The fund may accept other forms of guarantee from financial intermediaries in limited circumstances.

Fiduciaries and corporations are required to submit additional documents to sell fund shares.

The fund requires that you maintain a minimum account value of $500. If you hold less than $500 in your account, the fund reserves the right to notify you that it intends to sell your shares and close your account. You will be given 60 days from the date of the notice to make additional investments to avoid having your shares sold. This policy does not apply to certain qualified retirement plan accounts.

You may have difficulty contacting the fund by telephone or accessing www.pioneerinvestments.com during times of market volatility or disruption in telephone or Internet service. On New York Stock Exchange holidays or on days when the exchange closes early, Pioneer will adjust the hours for the telephone center and for online transaction processing accordingly. If you are unable to access www.pioneerinvestments.com or reach the fund by telephone, you should communicate with the fund in writing.

The fund does not offer share certificates. Shares are electronically recorded. Any existing certificated shares can only be sold by returning your certificate to the transfer agent, along with a letter of instruction or a stock power (a separate written authority transferring ownership) and a signature guarantee.

The fund declares dividends daily. The daily dividends consist of substantially all of the fund’s net income (excluding any net short- and long-term capital gains). You begin to earn dividends on the first business day following receipt of payment for shares. You continue to earn dividends up to and including the date of sale. Dividends are normally paid on the last business day of each month. The fund generally pays any distributions of net short- and long-term capital gains in November.

The fund may also pay dividends and capital gain distributions at other times if necessary for the fund to avoid U.S. federal income or excise tax. If you invest in the fund shortly before a distribution other than a daily dividend, generally you will pay a higher price per share, and, unless you are exempt from tax, you will pay taxes on the amount of the distribution whether you reinvest the distribution in additional shares or receive it as cash.

You will normally have to pay federal income taxes, and any state or local taxes, on the dividends and other distributions you receive from the fund, whether you take the distributions in cash or reinvest them in additional shares. For U.S. federal income tax purposes, distributions from the fund’s net capital gains are considered long-term capital gains and may be taxable to you at reduced rates. Distributions from the fund’s net short-term capital gains are taxable as ordinary income.

Other dividends are taxable either as ordinary income or, for taxable years beginning on or before December 31, 2012, if certain conditions, including holding period requirements, are met by the fund and the shareholder, as “qualified dividend income” taxable to individual shareholders at a maximum 15% U.S. federal income tax rate.

“Qualified dividend income” generally is income derived from dividends paid by U.S. corporations or certain foreign corporations that are either incorporated in a U.S. possession or eligible for tax benefits under certain U.S. income tax treaties. In addition, dividends that the fund receives in respect of stock of certain foreign corporations may be “qualified dividend income” if that stock is readily tradable on an established U.S. securities market.

A portion of dividends received from the fund (but none of the fund’s capital gain distributions) may qualify for the dividends-received deduction for corporations.

Since the fund’s income is derived primarily from sources that do not pay dividends, it is expected that only a limited portion, if any, of the dividends paid by the fund will qualify for the dividends-received deduction for corporations or the maximum 15% U.S. federal income tax rate available to individuals on “qualified dividend income.”

The fund will report to shareholders annually the U.S. federal income tax status of all fund distributions.

If the fund declares a dividend in October, November or December, payable to shareholders of record in such a month, and pays it in January of the following year, you will be taxed on the dividend as if you received it in the year in which it was declared.

When you sell or exchange fund shares you will generally recognize a capital gain or capital loss in an amount equal to the difference between the net amount of sale proceeds (or, in the case of an exchange, the fair market value of the shares) that you receive and your tax basis for the shares that you sell or exchange.

You must provide your social security number or other taxpayer identification number to the fund along with the certifications required by the Internal Revenue Service when you open an account. If you do not or if it is otherwise legally required to do so, the fund will apply “backup withholding” tax on your dividends and other distributions, sale proceeds and any other payments to you that are subject to backup withholding. The backup withholding rate is currently 28% and is scheduled to increase to 31% in 2013.

Distributions derived from interest on U.S. government obligations (but generally not distributions of gain from the sale of such obligations) may be exempt from certain state and local taxes.

You should ask your tax adviser about any federal, state, local and foreign tax considerations relating to an investment in the fund. You may also consult the fund’s statement of additional information for a more detailed discussion of the U.S. federal income tax considerations that may affect the fund and its shareowners.

Because the fund had not commenced operations as of the original date of this prospectus, financial highlights are not available.

You can obtain more free information about the fund from your investment firm or by writing to Pioneer Investment Management Shareholder Services, Inc., 60 State Street, Boston, Massachusetts 02109. You may also call 1-800-225-6292 for more information about the fund, to request copies of the fund’s statement of additional information and shareowner reports, and to make other inquiries.

The fund makes available the statement of additional information and shareowner reports, free of charge, on the fund’s website at www.pioneerinvestments.com. You also may find other information and updates about Pioneer and the fund, including fund performance information, on the fund’s website.

Annual and semiannual reports to shareowners, and quarterly reports filed with the Securities and Exchange Commission, provide additional information about the fund’s investments. The annual report discusses market conditions and investment strategies that significantly affected the fund’s performance during its last fiscal year.

The statement of additional information provides more detailed information about the fund.

The statement of additional information, and the independent registered public accounting firm’s report and financial statements in the fund’s annual report to shareholders, are incorporated by reference into this prospectus.

You can also review and copy the fund’s shareowner reports, prospectus and statement of additional information at the Securities and Exchange Commission’s Public Reference Room in Washington, D.C. Call 1-202-551-8090 for information. The Commission charges a fee for copies. You can get the same information free from the Commission’s EDGAR database on the Internet (http://www.sec.gov). You may also e-mail requests for these documents to publicinfo@sec.gov or make a request in writing to the Commission’s Public Reference Section, Washington, D.C. 20549-1520.


*Contents*
Fund Summary			3
More on the fund’s investment objectives and strategies			13
More on the risks of investing in the fund			21
Management			30
Pricing of shares			32
Choosing a class of shares			34
Distribution and service arrangements			35
Sales charges			37
Buying, exchanging and selling shares			44
Account options			53
Shareholder services and policies			56
Dividends, capital gains and taxes			62


(expenses that you pay each year as a percentage of the value of your investment)	Class A		Class C		Class Y
Management Fees		0.35%		0.35%		0.35%
Distribution and Service (12b-1) Fees		0.20%		1.00%		0.00%
Other Expenses¹		0.44%		0.44%		0.39%
Total Annual Fund Operating Expenses		0.99%		1.79%		0.74%
Less: Fee Waiver and Expense Reimbursement¹		–0.14%		–0.00%		–0.09%
Net Expenses²		0.85%		1.79%		0.65%


	If you redeem your shares				If you do not redeem your shares
	Number of years you own your shares
	1		3		1		3
Class A	$	335	$	544	$	335	$	544
Class C		282		563		182		563
Class Y		66		228		66		228


Investment adviser		Pioneer Investment Management, Inc.

Portfolio management		Charles Melchreit, Portfolio Manager and Vice President of Pioneer (portfolio manager of the fund since 2011). Seth Roman, Portfolio Manager and Vice President of Pioneer (portfolio manager of the fund since 2011). Jonathan Sharkey, Portfolio Manager and Vice President of Pioneer (portfolio manager of the fund since 2011).


	Sales charge as % of
Amount of purchase	Offering price		Net amount invested
Less than $50,000		2.50		2.56
$50,000 but less than $100,000		2.00		2.06
$100,000 but less than $250,000		1.50		1.52
$250,000 but less than $500,000		1.00		1.01
$500,000 or more		0		0


Receiving Bank:		State Street Bank and Trust Company
		225 Franklin Street
		Boston, MA 02101
		ABA Routing No. 011000028

For further credit to:		Shareholder Name
		Existing Pioneer Account No.
		Multi-Asset Floating Rate Fund