Nature of business and basis of presentation	3 Months Ended
Mar. 31, 2018
Nature of business and basis of presentation
Nature of business and basis of presentation	1. Nature of business and basis of presentation Mersana Therapeutics, Inc. is a clinical stage company located in Cambridge, Massachusetts. The Company is advancing a proprietary pipeline of targeted oncology therapeutics leveraging its Dolaflexin® antibody drug conjugate (ADC) platform. The Company’s first product candidate, XMT-1522, an ADC designed to address a much broader population of patients with HER2-expressing tumors than served by currently approved HER2 therapies, is currently in a Phase 1 dose escalation study. The Company’s second product candidate, XMT-1536, an ADC targeting NaPi2b, an antigen broadly expressed in certain types of cancer, is also in a Phase 1 dose escalation study. In addition, the Company has established a strategic partnership with Takeda Pharmaceutical Company Limited (Takeda) under which Takeda obtained rights to XMT‑1522 outside of the United States and Canada. The Company has also established strategic research and development partnerships with Takeda and Merck KGaA for the development and commercialization of additional ADC product candidates against a limited number of targets selected by the Company’s partners based on the Company’s Dolaflexin platform. The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development of technological innovations by competitors, reliance on third party manufacturers and the ability to transition from pilot-scale production to large-scale manufacturing of products. On July 3, 2017, the Company completed an initial public offering (IPO), in which the Company issued and sold 5,000,000 shares of its common stock at a public offering price of $15.00 per share, for aggregate gross proceeds of $75,000. The Company received $67,420 in net proceeds after deducting $7,580 of underwriting discounts and commissions and offering costs. On August 2, 2017, the Company issued and sold 51,977 shares of common stock at $15.00 per share for gross proceeds of $780 upon the partial exercise of the underwriters’ overallotment option. The Company received net proceeds of $725 after deducting $55 in underwriting discounts and commissions. In connection with preparing for the IPO, the Company effected a 1-for-4.5 reverse stock split of the Company’s common stock. The reverse stock split became effective on June 15, 2017. The par value and authorized shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split. All share and per share amounts in the financial statements and the notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital. The Company has incurred net losses since inception. The Company’s net loss was $12,403 for the three months ended March 31, 2018 and $38,707 for the year ended December 31, 2017. The Company expects to continue to incur operating losses for at least the next several years. As of March 31, 2018, the Company had an accumulated deficit of $112,312. The future success of the Company is dependent on its ability to identify and develop its product candidates, and ultimately upon its ability to attain profitable operations. The Company has devoted substantially all of its financial resources and efforts to research and development and general and administrative expense to support such research and development. The Company’s net losses may fluctuate significantly from quarter to quarter and year to year. Net losses and negative cash flows have had, and will continue to have, an adverse effect on the Company’s stockholders' deficit and working capital. The Company believes that its existing cash, cash equivalents and marketable securities as of March 31, 2018, will enable it to fund its operating plan into the second half of 2019, which the Company expects will allow it to achieve initial clinical data readouts for its two lead development programs. The Company’s unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2017 and the notes thereto, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC on March 28, 2018. The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of March 31, 2018, the results of its operations for the three months ended March 31, 2018 and 2017 and cash flows for the three months ended March 31, 2018 and 2017. Such adjustments are of a normal and recurring nature, other than the adjustments associated with the adoption of ASC Topic 606, Revenue from Contracts with Customers (Topic 606). The results for the three months ended March 31, 2018 are not necessarily indicative of the results for the year ending December 31, 2018, or for any future period. Effective January 1, 2018, the Company adopted the requirements of Topic 606 using the modified retrospective method as discussed below in Note 2: Summary of Significant Accounting Policies. All 2018 amounts and disclosures set forth in this Form 10-Q reflect these changes.

1. Nature of business and basis of presentation

Mersana Therapeutics, Inc. is a clinical stage company located in Cambridge, Massachusetts. The Company is advancing a proprietary pipeline of targeted oncology therapeutics leveraging its Dolaflexin® antibody drug conjugate (ADC) platform. The Company’s first product candidate, XMT-1522, an ADC designed to address a much broader population of patients with HER2-expressing tumors than served by currently approved HER2 therapies, is currently in a Phase 1 dose escalation study. The Company’s second product candidate, XMT-1536, an ADC targeting NaPi2b, an antigen broadly expressed in certain types of cancer, is also in a Phase 1 dose escalation study. In addition, the Company has established a strategic partnership with Takeda Pharmaceutical Company Limited (Takeda) under which Takeda obtained rights to XMT‑1522 outside of the United States and Canada. The Company has also established strategic research and development partnerships with Takeda and Merck KGaA for the development and commercialization of additional ADC product candidates against a limited number of targets selected by the Company’s partners based on the Company’s Dolaflexin platform.

The Company is subject to risks common to companies in the biotechnology industry, including but not limited to, risks of failure of preclinical studies and clinical trials, the need to obtain marketing approval for any drug product candidate that it may identify and develop, the need to successfully commercialize and gain market acceptance of its product candidates, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development of technological innovations by competitors, reliance on third party manufacturers and the ability to transition from pilot-scale production to large-scale manufacturing of products.

On July 3, 2017, the Company completed an initial public offering (IPO), in which the Company issued and sold 5,000,000 shares of its common stock at a public offering price of $15.00 per share, for aggregate gross proceeds of $75,000. The Company received $67,420 in net proceeds after deducting $7,580 of underwriting discounts and commissions and offering costs. On August 2, 2017, the Company issued and sold 51,977 shares of common stock at $15.00 per share for gross proceeds of $780 upon the partial exercise of the underwriters’ overallotment option. The Company received net proceeds of $725 after deducting $55 in underwriting discounts and commissions.

In connection with preparing for the IPO, the Company effected a 1-for-4.5 reverse stock split of the Company’s common stock. The reverse stock split became effective on June 15, 2017. The par value and authorized shares of common stock and convertible preferred stock were not adjusted as a result of the reverse stock split. All share and per share amounts in the financial statements and the notes thereto have been retroactively adjusted for all periods presented to give effect to this reverse stock split, including reclassifying an amount equal to the reduction in par value of common stock to additional paid-in capital.

The Company has incurred net losses since inception. The Company’s net loss was $12,403 for the three months ended March 31, 2018 and $38,707 for the year ended December 31, 2017. The Company expects to continue to incur operating losses for at least the next several years. As of March 31, 2018, the Company had an accumulated deficit of $112,312. The future success of the Company is dependent on its ability to identify and develop its product candidates, and ultimately upon its ability to attain profitable operations. The Company has devoted substantially all of its financial resources and efforts to research and development and general and administrative expense to support such research and development. The Company’s net losses may fluctuate significantly from quarter to quarter and year to year. Net losses and negative cash flows have had, and will continue to have, an adverse effect on the Company’s stockholders' deficit and working capital. The Company believes that its existing cash, cash equivalents and marketable securities as of March 31, 2018, will enable it to fund its operating plan into the second half of 2019, which the Company expects will allow it to achieve initial clinical data readouts for its two lead development programs.

The Company’s unaudited condensed consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the United States (U.S. GAAP) and the rules and regulations of the Securities and Exchange Commission (SEC). Any reference in these notes to applicable guidance is meant to refer to the authoritative United States generally accepted accounting principles as found in the Accounting Standards Codification (ASC) and Accounting Standards Updates (ASU) of the Financial Accounting Standards Board (FASB). Certain information and footnote disclosures normally included in financial statements prepared in accordance with U.S. GAAP have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these financial statements should be read in conjunction with the audited financial statements as of and for the year ended December 31, 2017 and the notes thereto, included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2017 filed with the SEC on March 28, 2018.

The unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements. In the opinion of the Company’s management, the accompanying unaudited condensed consolidated financial statements contain all adjustments which are necessary to present fairly the Company’s financial position as of March 31, 2018, the results of its operations for the three months ended March 31, 2018 and 2017 and cash flows for the three months ended March 31, 2018 and 2017. Such adjustments are of a normal and recurring nature, other than the adjustments associated with the adoption of ASC Topic 606, Revenue from Contracts with Customers (Topic 606). The results for the three months ended March 31, 2018 are not necessarily indicative of the results for the year ending December 31, 2018, or for any future period.

Effective January 1, 2018, the Company adopted the requirements of Topic 606 using the modified retrospective method as discussed below in Note 2: Summary of Significant Accounting Policies. All 2018 amounts and disclosures set forth in this Form 10-Q reflect these changes.