2.	Summary of Significant Accounting Policies

Basis of Presentation

The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (U.S. GAAP). The accompanying consolidated financial statements include the accounts of Sierra Oncology, Inc. and its wholly-owned subsidiaries. All intercompany accounts and transactions have been eliminated in consolidation.

Use of Estimates

The preparation of the consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of consolidated financial statements and the reported amounts of expense during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to the fair value of stock options issued, accruals such as research and development costs, the fair value of common stock, the fair value of preferred stock, the fair value of preferred stock warrant liabilities, and recoverability of the Company’s net deferred tax assets, and related valuation allowance. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.

Foreign Currency

The functional currency of the Company’s foreign subsidiaries is the U.S. Dollar. Transactions denominated in currencies other than the functional currency are recorded at prevailing exchange rates during the period. At the end of each reporting period, monetary assets and liabilities are remeasured to the functional currency using exchange rates in effect at the balance sheet date. Non-monetary assets and liabilities are recorded at historical exchange rates. Gains and losses related to remeasurement are recorded in other income (expense) in the consolidated statements of operations. The net foreign exchange transaction losses included in other income (expense) in the accompanying consolidated statements of operations were $0.1 million for the years ended December 31, 2017 and 2016, and insignificant for the year ended December 31, 2015.

Cash and Cash Equivalents

The Company considers all highly liquid investments with an original maturity of three months or less from the date of purchase to be cash equivalents. Cash and cash equivalents consist primarily of funds invested in readily available checking and savings accounts and highly liquid investments in money market funds.

Restricted Cash

Restricted cash represents collateral for a corporate credit card facility and security deposit required for a facility lease. Restricted cash consists of funds invested in a money market fund. As of December 31, 2017 and December 31, 2016, restricted cash of $0.2 million was included in other assets in the accompanying consolidated balance sheets.

Concentrations of Credit Risk

Financial instruments that subject the Company to significant concentrations of credit risk consist of cash, cash equivalents and restricted cash. All of the Company’s cash, cash equivalents and restricted cash are held at financial institutions in the United States and Canada that management believes to be of high credit quality. Deposits held in the United States and Canada with these financial institutions exceed federally insured limits. The Company’s cash, cash equivalents and restricted cash exceeded federally insured limits by $100.0 million and $108.7 million at December 31, 2017 and 2016, respectively.

The primary focus of the Company’s investment strategy is to preserve capital and meet liquidity requirements. The Company’s investment policy addresses the level of credit exposure by limiting the concentration in any one corporate issuer and establishing a minimum allowable credit rating.

Fair Value of Financial Instruments

The Company’s cash and cash equivalents, restricted cash, other current assets, accounts payable, and accrued liabilities approximate their fair value at December 31, 2017 and 2016, due to their short duration.

The Company utilizes valuation techniques that maximize the use of observable inputs and minimize the use of unobservable inputs to the extent possible. The Company determines the fair value of its financial instruments based on assumptions that market participants would use in pricing an asset or liability in the principal or most advantageous market. When considering market participant assumptions in fair value measurements, the following fair value hierarchy distinguishes between observable and unobservable inputs, which are categorized in one of the following levels:

Level 1—Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date;

Level 2—Inputs are observable, unadjusted quoted prices in active markets for similar assets or liabilities, unadjusted quoted prices for identical or similar assets or liabilities in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3—Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.

Property and Equipment, Net

Property and equipment, net are stated at cost, less accumulated depreciation. Depreciation on property and equipment, excluding leasehold improvements, is computed using the straight-line method over the estimated useful lives of the respective assets, generally three to five years. Depreciation begins at the time the asset is placed in service. Maintenance and repairs are charged to operations as incurred. Upon sale or retirement of assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in the consolidated statement of operations. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term.

Other Assets

Other assets consist primarily of restricted cash pledged as collateral for a corporate credit card facility, long-term prepaid rent and refundable security deposits required for facility leases.

Preferred Stock Warrant Liabilities

The Company accounted for its warrants issued in connection with its various financing transactions based upon the characteristics and provisions of the instrument. Warrants classified as derivative liabilities were recorded on the Company’s consolidated balance sheets at their fair value on the date of issuance and remeasured to fair value on each subsequent reporting period, with the changes in fair value recognized as a component of other income (expense), net in the accompanying consolidated statements of operations. On the closing of the IPO on July 21, 2015 (discussed in Note 1), all outstanding warrants were exercised and the liability on the preferred stock warrants was reclassified to additional paid-in capital in stockholders’ equity and was no longer subject to remeasurement.

Research and Development Costs

Research and development costs are expensed as incurred. The Company accounts for non-refundable advance payments for goods and services that will be used in future research and development activities as expenses when the goods have been received or when the service has been performed rather than when the payment is made. Depending on the timing of payments to service providers of research and development costs, the Company recognizes prepaid expenses or accrued expenses related to these costs. These prepaid or accrued expenses are based on management’s estimates of the work performed under service agreements and milestones achieved. In the event that a clinical trial is terminated early, the Company records an accrual for the estimated remaining costs to complete the trial in the period of termination.

Upfront payments made in connection with license agreements are expensed as research and developments costs, as the assets acquired do not have alternative future use. Contingent milestone payment obligations due to third parties under license agreements are expensed when the milestones are considered probable of occurring.

Research and development costs include fees incurred in connection with license agreements, compensation and other related costs for employees engaged in research and development, costs associated with research and preclinical studies, clinical trials, regulatory activities, manufacturing activities to support clinical activities, fees paid to external service providers that conduct certain research and development, clinical, and manufacturing activities on behalf of the Company and an allocation of overhead expenses.

Stock-Based Compensation

The Company accounts for share-based payments at fair value, which is measured using the Black-Scholes option-pricing model. For share-based awards that vest subject to the satisfaction of a service requirement, the fair value measurement date for employee stock-based compensation awards is the date of grant and the expense is recognized on a straight-line basis, over the vesting period.

For share-based awards that vest subject to the satisfaction of a service requirement and a performance component, the fair value measurement date is the date of grant and is recognized over the requisite service period as achievement of the performance objective becomes probable.

Stock-based compensation arrangements with non-employees are recognized at the grant date and remeasured to fair value at each reporting period. The expense is recognized over the vesting period which is generally the service period.

Income Taxes

The Company uses the asset and liability method of accounting for income taxes. Under this method, deferred tax assets and liabilities are determined based on the differences between the financial reporting and the tax bases of assets and liabilities and are measured using the enacted tax rates and laws that will be in effect when the differences are expected to reverse. Management makes an assessment of the likelihood that the resulting deferred tax assets will be realized. A valuation allowance is provided when it is more likely than not that some portion or all of a deferred tax asset will not be realized. Due to the Company’s historical operating performance and the recorded cumulative net losses in prior fiscal periods, the net U.S. deferred tax assets have been offset by a full valuation allowance.

The Company recognizes uncertain income tax positions at the largest amount that is more likely than not to be sustained upon audit by the relevant taxing authority. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained. Changes in recognition or measurement are reflected in the period in which judgment occurs. The Company’s policy is to recognize interest and penalties related to the underpayment of income taxes as a component of provision for income taxes.

Segment Information

Operating segments are components of an enterprise for which separate financial information is available and is evaluated regularly by the Company’s chief operating decision maker in deciding how to allocate resources and assessing performance. The Company’s chief operating decision maker is its Chief Executive Officer.

The Company’s Chief Executive Officer views the Company’s operations and manages its business in one operating segment, which is the business of researching, developing, and commercializing therapies for the treatment of patients with cancer. Accordingly, the Company has a single reporting segment.

Recent Accounting Pronouncements

In February 2016, the Financial Accounting Standards Board (FASB) issued FASB Accounting Standards Update (ASU) No. 2016-02, Leases (Topic 842). The amendments in this update require that organizations recognize lease assets and lease liabilities on the balance sheet and disclose key information about leasing arrangements. This ASU is effective for financial statements issued for fiscal years beginning after December 15, 2018, and interim periods within those fiscal years, with early adoption permitted. The Company will adopt the new standard effective January 1, 2019 and expect its operating leases, as disclosed in Note 6 “Commitments and Contingencies”, to be subject to the new standard. The Company will recognize right-of-use assets and operating lease liabilities on its consolidated balance sheets upon adoption, which will increase its total assets and liabilities.