Verastem (VSTM) 10-K 23 Mar 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($)	12 Months Ended
	Dec. 31, 2016	Mar. 15, 2017	Jun. 30, 2016
Document and Entity Information
Entity Registrant Name	Verastem, Inc.
Entity Central Index Key	1,526,119
Document Type	10-K
Document Period End Date	Dec. 31, 2016
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Smaller Reporting Company
Entity Public Float			$ 47,609,884
Entity Common Stock, Shares Outstanding		36,992,418
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($)	Dec. 31, 2016	Dec. 31, 2015
Current assets:
Cash and cash equivalents	$ 32,349,000	$ 24,870,000
Short-term investments	48,548,000	85,388,000
Prepaid expenses and other current assets	398,000	585,000
Total current assets	81,295,000	110,843,000
Property and equipment, net	1,417,000	2,048,000
Restricted cash	162,000	203,000
Other assets	755,000
Total assets	83,629,000	113,094,000
Current liabilities:
Accounts payable	4,095,000	3,942,000
Accrued expenses	6,896,000	6,098,000
Liability classified stock-based compensation awards	0	69,000
Total current liabilities	10,991,000	10,109,000
Other liabilities	341,000	516,000
Stockholders' equity
Preferred stock, $0.0001 par value; 5,000 shares authorized, no shares issued and outstanding at December 31, 2016 and 2015, respectively
Common stock, $0.0001 par value; 100,000 shares authorized, 36,992 and 36,941 shares issued and outstanding at December 31, 2016 and 2015, respectively	4,000	4,000
Additional paid-in capital	307,587,000	301,305,000
Accumulated other comprehensive income	29,000	43,000
Accumulated deficit	(235,323,000)	(198,883,000)
Total stockholders' equity	72,297,000	102,469,000
Total liabilities and stockholders' equity	$ 83,629,000	$ 113,094,000

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - $ / shares shares in Thousands	Dec. 31, 2016	Dec. 31, 2015
CONSOLIDATED BALANCE SHEETS
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized	100,000	100,000
Common stock, shares issued	36,992	36,941
Common stock, shares outstanding	36,992	36,941

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 19,779	$ 40,565	$ 35,448
General and administrative	17,223	17,634	18,159
Total operating expenses	37,002	58,199	53,607
Loss from operations	(37,002)	(58,199)	(53,607)
Interest income	562	334	242
Net loss	$ (36,440)	$ (57,865)	$ (53,365)
Net loss per share - basic and diluted	$ (0.99)	$ (1.61)	$ (2.07)
Weighted-average number of common shares used in net loss per share-basic and diluted	36,988,000	35,932,000	25,804,000
Net loss	$ (36,440)	$ (57,865)	$ (53,365)
Unrealized (loss) gain on available-for-sale securities	(14)	32	(17)
Comprehensive loss	$ (36,454)	$ (57,833)	$ (53,382)

CONSOLIDATED STATEMENTS OF STOC

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common stockFollow-on offering	Common stockAt The Market Equity Offering Program	Common stock	Additional paid-in capitalFollow-on offering	Additional paid-in capitalAt The Market Equity Offering Program	Additional paid-in capital	Accumulated other comprehensive (loss) income	Accumulated deficit	Follow-on offering	At The Market Equity Offering Program	Total
Balance at Dec. 31, 2013			$ 3			$ 205,068	$ 28	$ (87,653)			$ 117,446
Balance (in shares) at Dec. 31, 2013			25,328,450
Increase (Decrease) in Stockholders' Equity
Net loss								(53,365)			(53,365)
Unrealized gain (loss) on available-for-sale marketable securities							(17)				(17)
Issuance of common stock, net of issuance costs						11,646					11,646
Issuance of common stock, net of issuance costs (in shares)			1,346,676
Vesting of restricted stock						9					9
Vesting of restricted stock (in shares)			321,287
Issuance of common stock resulting from exercise of stock options						20					20
Issuance of common stock resulting from exercise of stock options (in shares)			30,451
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings						(780)					(780)
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings (in shares)			135,008
Shares issued for technology rights						1,447					1,447
Shares issued for technology rights (in shares)			97,500
Stock-based compensation expense						12,360					12,360
Balance at Dec. 31, 2014			$ 3			229,770	11	(141,018)			88,766
Balance (in shares) at Dec. 31, 2014			27,259,372
Increase (Decrease) in Stockholders' Equity
Net loss								(57,865)			(57,865)
Unrealized gain (loss) on available-for-sale marketable securities							32				32
Issuance of common stock, net of issuance costs	$ 1			$ 50,941	$ 10,911				$ 50,942	$ 10,911
Issuance of common stock, net of issuance costs (in shares)	8,337,500	1,189,479								1,189,479
Vesting of restricted stock						2					2
Vesting of restricted stock (in shares)			7,995
Issuance of common stock resulting from exercise of stock options						13					13
Issuance of common stock resulting from exercise of stock options (in shares)			33,658
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings						(417)					(417)
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings (in shares)			113,257
Stock-based compensation expense						10,085					10,085
Balance at Dec. 31, 2015			$ 4			301,305	43	(198,883)			$ 102,469
Balance (in shares) at Dec. 31, 2015			36,941,261								36,941,000
Increase (Decrease) in Stockholders' Equity
Net loss								(36,440)			$ (36,440)
Unrealized gain (loss) on available-for-sale marketable securities							(14)				(14)
Issuance of common stock, net of issuance costs (in shares)										0
Issuance of common stock resulting from exercise of stock options (in shares)			1,605
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings						(5)					(5)
Issuance of common stock resulting from vesting of restricted stock units and payment of tax withholdings (in shares)			49,552
Stock-based compensation expense						6,287					6,287
Balance at Dec. 31, 2016			$ 4			$ 307,587	$ 29	$ (235,323)			$ 72,297
Balance (in shares) at Dec. 31, 2016			36,992,418								36,992,000

CONSOLIDATED STATEMENTS OF STO6

CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
Issuance of common stock, issuance costs	$ 53	$ 43

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net Cash Provided by (Used in) Operating Activities
Net loss	$ (36,440)	$ (57,865)	$ (53,365)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	670	754	427
Stock-based compensation expense	6,287	10,085	12,360
Amortization of premiums and discounts on available-for-sale marketable securities	(140)	264	290
Non-cash expense related to purchase of technology rights			1,197
Loss on disposal of fixed assets		46	4
Changes in operating assets and liabilities:
Prepaid expenses, other current assets and other assets	(568)	276	27
Accounts payable	153	863	287
Accrued expenses and other liabilities	623	418	2,119
Liability classified stock-based compensation awards	(69)	(400)	(248)
Net cash used in operating activities	(29,484)	(45,559)	(36,902)
Investing activities
Purchases of property and equipment	(39)	(211)	(2,429)
Purchase of investments	(82,101)	(199,851)	(39,361)
Maturities of investments	119,067	173,005	85,047
Decrease (increase) in restricted cash	41		(117)
Net cash provided by (used in) investing activities	36,968	(27,057)	43,140
Financing activities
Proceeds from the exercise of stock options		13	20
Net proceeds from the issuance of common stock and restricted common stock		63,989	9,534
Cash used to settle restricted stock liability	(5)	(417)	(780)
Net cash (used in) provided by financing activities	(5)	63,585	8,774
Increase (decrease) in cash and cash equivalents	7,479	(9,031)	15,012
Cash and cash equivalents at beginning of period	24,870	33,901	18,889
Cash and cash equivalents at end of period	$ 32,349	$ 24,870	33,901
Supplemental disclosure of non-cash investing and financing activities
Proceeds from the issuance of common stock included in prepaid expenses and other current assets			2,085
Purchase of property and equipment in accounts payable			$ 196

Nature of business

Nature of business	12 Months Ended
	Dec. 31, 2016
Nature of business
Nature of business	1. Nature of business Verastem, Inc. (the Company) is a biopharmaceutical company focused on discovering and developing drugs to improve outcomes for patients with cancer. The Company’s operations to date have been limited to organizing and staffing the Company, business planning, raising capital, acquiring and developing its technology, identifying potential product candidates and undertaking preclinical and clinical studies of its product candidates. The Company is subject to a number of risks similar to other life science companies, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, inability to obtain marketing approval of product candidates, competitors developing new technological innovations, market acceptance of the Company’s products and protection of proprietary technology. If the Company does not successfully commercialize any of its product candidates, it will be unable to generate product revenue or achieve profitability. As of December 31, 2016, the Company had cash, cash equivalents and investments of $80.9 million and accumulated deficit of $235.3 million. Although the Company has incurred recurring losses and expects to continue to incur losses for the foreseeable future, the Company expects its cash, cash equivalents and investments to be sufficient to fund its current operating plan for at least the next twelve months from the date of issuance of these consolidated financial statements and into 2018.

Significant accounting policies

Significant accounting policies	12 Months Ended
	Dec. 31, 2016
Significant accounting policies.
Significant accounting policies	2. Significant accounting policies Basis of consolidation The consolidated financial statements include the accounts of Verastem Securities Company, a wholly owned subsidiary of the Company. All financial information presented has been consolidated and includes the accounts of the Company and its wholly owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation. Use of estimates The preparation of the Company’s financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including estimates related to accruals and stock‑based compensation expense. The Company bases its estimates on historical experience and other market‑specific or other relevant assumptions that it believes to be reasonable. Actual results could differ from such estimates. Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available and regularly reviewed by the chief operating decision maker, or decision‑making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing drugs for the treatment of cancer. All material long-lived assets of the Company reside in the United States. Cash and cash equivalents The Company considers all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies. Cash equivalents are reported at fair value. Fair value of financial instruments The Company determines the fair value of its financial instruments based upon the fair value hierarchy, which prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 inputs Quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. Level 2 inputs Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — December 31, 2015 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — Financial liabilities Liability classified stock-based compensation awards $ $ $ — $ — Total financial liabilities $ $ $ — $ — These investments and cash equivalents have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The Company validates the prices provided by third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2016 and 2015. The Company’s liability classified stock-based compensation awards were comprised of restricted stock units (RSUs) that allowed for greater than minimum statutory tax withholdings. These awards were valued based on the fair value of the Company’s common stock underlying the awards, which is traded on an active market. During the first quarter of 2013, the Company amended the terms of certain RSUs to allow for cash tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs were considered to be liability instruments. As a result of this modification, the Company recorded a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the statement of operations. The Company recorded stock-based compensation expense equal to the greater of the original grant date fair value of the awards or the settlement date fair value. All such RSUs were fully vested as of February 1, 2016. During the years ended December 31, 2016 and 2015, the Company made approximate deposits to the taxing authorities of $5,000 and $417,000, respectively, to settle the tax liability for awards that settled during such periods. Investments Investments and cash equivalents consist of investments in a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies that are classified as available‑for‑sale pursuant to Accounting Standards Codification (ASC) Topic 320, Investments—Debt and Equity Securities . The Company classifies investments available to fund current operations as current assets on its consolidated balance sheets. Investments are classified as long‑term assets on the consolidated balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Investments are carried at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit), until such gains and losses are realized. The fair value of these securities is based on quoted prices for identical or similar assets. If a decline in the fair value is considered other‑than‑temporary, based on available evidence, the unrealized loss is transferred from other comprehensive loss to the consolidated statements of operations and comprehensive loss. The Company reviews investments for other‑than‑temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other‑than‑temporary, the Company considers the intent to sell, or whether it is more likely than not that the Company will be required to sell, the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to year end. As of December 31, 2016 and 2015, there were no investments with a fair value that was significantly lower than the amortized cost basis or any investments that had been in an unrealized loss position for a significant period. There were no other‑than‑temporary declines in fair value of short‑term investments for the years ended December 31, 2016, 2015 and 2014. Realized gains and losses are determined using the specific identification method and are included in interest income in the consolidated statements of operations and comprehensive loss. There were no realized gains or losses recognized for the years ended December 31, 2016, 2015 and 2014. Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Overnight repurchase agreements $ — $ — Total cash and cash equivalents $ $ — $ — $ Investments: Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $ December 31, 2015 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Government-sponsored enterprise securities (original maturities within 90 days) — — Corporate bonds and commercial paper (original maturities within 90 days) — — Total cash and cash equivalents $ $ — $ — $ Investments: Government-sponsored enterprise securities (due within 1 year) $ $ $ — $ Treasury securities (due within 1 year) — — Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $ Concentrations of credit risk and off‑balance sheet risk Cash and cash equivalents and investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company mitigates this risk by maintaining its cash and cash equivalents and investments with high quality, accredited financial institutions. The management of the Company’s investments is not discretionary on the part of these financial institutions. As of December 31, 2016, the Company’s cash, cash equivalents and investments were deposited at two financial institutions and it has no significant off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements. Property and equipment Property and equipment consists of laboratory equipment, office furniture, computer equipment and leasehold improvements. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization is calculated using the straight‑line method over the following estimated useful lives of the assets: Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold Improvements Lesser of useful life or life of lease Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized. The Company reviews its long‑lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of assets may not be recoverable. Recoverability is measured by comparison of the asset’s book value to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No material impairment losses have been recorded through December 31, 2016. Other assets Pursuant to the license agreement between the Company and Infinity Pharmaceuticals, Inc. ( Infinity ) amended and restated on November 1, 2016, effective as of October 29, 2016 (the License Agreement), the Company assumed the rights to the remaining balance of certain prepaid amounts as of December 31, 2016 on contracts with contract research organizations (CROs). The License Agreement also requires the Company to reimburse Infinity for these prepaid CRO expenses. The prepaid CRO expenses and corresponding liability of approximately $755,000 are recorded as other assets and accrued expenses on the consolidated balance sheets as of December 31, 2016. Research and development costs The Company expenses research and development costs to operations as incurred. Research and development expenses consist of: · employee‑related expenses, including salaries, benefits, travel and stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as CROs, clinical trial sites, manufacturing organizations and consultants, including the scientific advisory board; · license fees; and · facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, depreciation of equipment, and laboratory supplies. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made. Stock‑based compensation The Company expenses the fair value of employee stock-based awards over the requisite service period, which typically is the vesting period. Compensation expense is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted annually to reflect actual forfeitures. Awards subject to performance based vesting requirements are expensed utilizing an accelerated attribution model if achievement of the performance criteria is determined to be probable. The grant date fair value of employee stock options is estimated using the Black‑Scholes option pricing model that takes into account the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the Securities and Exchange Commission Staff Accounting Bulletin Topic 14.D.2 to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post‑vesting termination behavior among its employee population. The computation of expected volatility is based on the historical volatility of five companies equally weighted, including the Company and a representative group of four public biotechnology and life sciences companies with similar characteristics to the Company, including similar stage of product development and therapeutic focus. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. Management assesses expected forfeitures based on the experience of the Company coupled with comparison to data from the representative group of companies and recognizes compensation costs only for those equity awards expected to vest. Stock‑based awards issued to nonemployees, including directors for non‑board related services, are accounted for based on the fair value of such services received or of the equity instruments issued, whichever is more reliably measured. Stock option awards to non-employees are revalued at each reporting date and upon vesting using the Black‑Scholes option pricing model and are expensed on a straight‑line basis over the vesting period. Stock‑based compensation awards which allowed for greater than the minimum statutory tax withholdings were classified as liabilities. These awards were revalued at each reporting date and were expensed on a straight‑line basis over the vesting period. Upon settlement, the awards were revalued and the amounts were reclassified to additional paid‑in capital. Shares were withheld to cover the tax withholding and amounts paid to settle the tax liability were recorded as a reduction of additional paid‑in capital. Income taxes The Company accounts for income taxes under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Tax benefits are recognized when it is more likely than not that a tax position will be sustained during an audit. Deferred tax assets are reduced by a valuation allowance if current evidence indicates that it is considered more likely than not that these benefits will not be realized. Net loss per share Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options, restricted stock units, unvested restricted stock and the warrant issued in 2014 are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. All potentially dilutive securities were excluded from the calculation of diluted net loss per share as the securities were anti‑dilutive for all periods presented. The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti‑dilutive effect: Year Ended December 31, 2016 2015 2014 Outstanding stock options Outstanding warrants Unvested restricted stock units — Unvested restricted stock — — Recently Issued Accounting Standards Updates In November 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In October 2016, the FASB issued ASU 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control . ASU 2016-17 updates ASU 2015-02. Under the amendments, a single decision maker is not required to consider indirect interests held through related parties that are under common control with the single decision maker to be the equivalent of direct interests in their entirety. Instead, a single decision maker is required to include those interests on a proportionate basis consistent with indirect interests held through other related parties. ASU 2016-17 is effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In August 2016, FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . ASU 2016-09 simplifies the accounting for share-based compensation arrangements, including the income tax impact and classification on the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2016 with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which supersedes the guidance under FASB ASC Topic 840, Leases , resulting in the creation of FASB ASC Topic 842, Leases. ASU 2016-02 requires lessees to recognize in the statement of financial position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term for both finance and operating leases. The guidance also eliminates the current real estate-specific provisions for all entities. ASU 2016-02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018 with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. Recently Adopted Accounting Standards Updates In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. ASU 2017-01 clarifies the definition of a business, provides a screen to determine when a set of assets is not a business and narrows the definition of the term output. ASU 2017-01 is effective for the interim and annual periods after December 15, 2016. Early adoption is permitted. The Company has elected to early adopt ASU 2017-01 and to apply it to the November 2016 amended and restated license agreement with Infinity, under which it acquired an exclusive worldwide license for the research, development, commercialization, and manufacture of products in oncology indications containing duvelisib. In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements - Going Concern: Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (Subtopic 205-40). ASU 2014-15 requires management to assess an entity’s ability to continue as a going concern every reporting period, and provide certain disclosures if management has substantial doubt about the entity’s ability to operate as a going concern, or an express statement if not, by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. ASU 2014-15 is effective for the interim and annual periods after December 15, 2016. Early adoption is permitted. The Company adopted ASU 2014-15 effective October 1, 2016. The Company has evaluated the impact of the adoption of ASU 2014-15 on its year ended December 31, 2016 consolidated financial statements and determined that there is not substantial doubt about the Company’s ability to continue as a going concern for at least one year from the issuance of the December 31, 2016 consolidated financial statements.

Property and equipment

Property and equipment	12 Months Ended
	Dec. 31, 2016
Property and equipment
Property and equipment	3. Property and equipment, net Property and equipment and related accumulated depreciation are as follows (in thousands): December 31, December 31, 2016 2015 Leasehold improvements $ $ Laboratory equipment Furniture and fixtures Computer equipment Less: accumulated depreciation $ $ Approximate total depreciation and amortization expenses amounted to $670,000, $754,000, and $427,000 for the years ended December 31, 2016, 2015 and 2014, respectively.

Prepaid expenses and other curr

Prepaid expenses and other current assets	12 Months Ended
	Dec. 31, 2016
Prepaid expenses and other current assets
Prepaid expenses and other current assets	4. Prepaid expenses and other current assets Prepaid expenses and other current assets consist of the following (in thousands): December 31, December 31, 2016 2015 Interest receivable $ $ Prepaid contract research organization costs Prepaid insurance Prepaid other $ $

Accrued expenses

Accrued expenses	12 Months Ended
	Dec. 31, 2016
Accrued expenses
Accrued expenses	5. Accrued expenses Accrued expenses consist of the following (in thousands): December 31, 2016 December 31, 2015 Contract research organization costs $ $ Compensation and related benefits Consulting fees — Professional fees Deferred rent Other $ $

Common stock

Common stock	12 Months Ended
	Dec. 31, 2016
Common stock.
Common stock	6. Common stock As of December 31, 2016 and 2015, the Company had reserved the following shares of common stock for the issuance of common stock for vested restricted stock units, the exercise of stock options, and an outstanding warrant (in thousands): December 31, December 31, 2016 2015 Shares reserved under equity compensation plans Shares reserved for inducement grants Shares reserved for outstanding warrants Each share of common stock is entitled to one vote. The holders of the common stock are also entitled to receive dividends whenever funds are legally available and when declared by the board of directors. At-the-market equity offering program In December 2013, the Company established an at-the-market equity offering program pursuant to which it was able to offer and sell up to $35.0 million of its common stock at then current market prices from time to time. In November 2014, the Company commenced sales under this program. During the year ended December 31, 2015, the Company sold 1,189,479 shares of common stock under this program with net proceeds (after deducting commissions and other offering expenses) of $12.9 million. No additional sales of the Company’s common stock were made under this program and no proceeds were received during the year ended December 31, 2016. Warrant In February 2014, in connection with the acquisition of intellectual property rights from Encarta, Inc. (Encarta), the Company issued a warrant to purchase 142,857 shares of common stock exercisable at a price of $17.16 per share that expires 3 years from the issuance date. The warrant expired unexercised in February 2017.

Stock-based compensation

Stock-based compensation	12 Months Ended
	Dec. 31, 2016
Stock-based compensation
Stock-based compensation	7. Stock‑based compensation Stock‑based compensation expense as reflected in the Company’s consolidated statements of operations and comprehensive loss was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ $ $ General and administrative Total stock-based compensation expense $ $ $ Of the $6.2 million of stock-based compensation expense recorded during the year ended December 31, 2016, $6.3 million was recorded to additional paid-in capital and approximately $69,000 was recorded as a decrease in liability classified awards. Of the $9.7 million of stock-based compensation expense recorded during the year ended December 31, 2015, $10.1 million was recorded to additional paid-in capital and approximately $400,000 was recorded as a decrease in liability classified awards. Of the $12.1 million of stock-based compensation expense recorded during the year ended December 31, 2014, approximately $12.3 million was recorded to additional paid-in capital and approximately $248,000 was recorded as a decrease in liability classified awards. The Company has awards outstanding under two equity compensation plans, the 2012 Incentive Plan (the 2012 Plan) and the 2010 Equity Incentive Plan (the 2010 Plan), as well as the inducement award program. Terms of stock award agreements, including vesting requirements, are determined by the board of directors, subject to the provisions of the individual plans. To date, most options granted by the Company vest twenty-five percent (25%) one year from vesting start date and six and a quarter percent (6.25%) for each successive three-month period, thereafter (subject to acceleration of vesting in the event of certain change of control transactions) and are exercisable for a period of ten years from the date of grant. 2012 Incentive Plan The 2012 Plan became effective immediately upon the closing of the Company’s IPO in February 2012. Upon effectiveness of the 2012 Plan, the Company ceased making awards under the 2010 Plan. The 2012 Plan initially allowed the Company to grant awards for up to 3,428,571 shares of common stock, plus the number of shares of common stock available for grant under the 2010 Plan as of the effectiveness of the 2012 Plan (which was an additional 30,101 shares), plus that number of shares of common stock related to awards outstanding under the 2010 Plan which terminate by expiration, forfeiture, cancellation or otherwise. The 2012 Plan includes an “evergreen provision” that allows for an annual increase in the number of shares of common stock available for issuance under the 2012 Plan. The annual increase is added on the first day of each year beginning in 2013 and each subsequent anniversary until the expiration of the 2012 Plan, and is equal to the lower of 1,285,714 shares of common stock, 4.0% of the number of shares of common stock outstanding and an amount determined by the board of directors. On January 1, 2016 and 2015, the number of shares available for issuance under the 2012 Plan increased by 1,285,714 and 1,081,045, respectively, under this provision. Subsequently, on January 1, 2017, the number of shares available for issuance under the 2012 Plan increased by 1,285,714 under this provision. Awards under the 2012 Plan may include the following award types: incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock units (RSUs), other stock‑based or cash‑based awards and any combination of the foregoing. As of December 31, 2016, under the 2012 Plan, the Company has granted stock options for 7,874,773 shares of common stock, of which 2,672,751 have been forfeited and restricted stock units for 909,918 shares of common stock, of which 150,101 have been forfeited. The exercise price of each option has been equal to the closing price of a share of our common stock on the grant date. Inducement Award Program In December 2014, the Company established an inducement award program (in accordance with NASDAQ Listing Rule 5635(c)(4)) under which it may grant non-statutory stock options to purchase up to an aggregate of 750,000 shares of common stock to new or prospective employees as inducement to enter into employment with the Company. In December 2016, the Board of Directors authorized and reserved 580,000 additional shares of common stock under this program. The program is governed by the terms of the 2012 Plan but does not fall under the 2012 Plan. As of December 31, 2016 and 2015, the Company had granted 580,000 and 210,000 shares of common stock under the program, respectively. As of December 31, 2016 and 2015, 75,000 of the options issued under this program had been cancelled and 750,000 remain available for future issuance. Stock Options A summary of the Company’s stock option activity and related information for the year ended December 31, 2016 is as follows: Weighted-average Weighted-average remaining Aggregate exercise price per contractual term intrinsic value Shares share (years) (in thousands) Outstanding at December 31, 2015 $ $ Granted $ Exercised $ Forfeited/cancelled $ Outstanding at December 31, 2016 $ $ Vested at December 31, 2016 $ $ Vested and expected to vest at December 31, 2016(1) $ $ (1) This represents the number of vested options as of December 31, 2016, plus the number of unvested options expected to vest as of December 31, 2016, based on the unvested options at December 31, 2016, adjusted for the estimated forfeiture rate. The fair value of each employee stock option was estimated at the date of grant using a Black‑Scholes option‑pricing model with the following assumptions: Year Ended December 31, 2016 2015 2014 Risk-free interest rate % % % Volatility % % % Dividend yield — — — Expected term (years) The Company recorded stock‑based compensation expense associated with employee stock options of $6.1 million, $7.9 million, and $7.8 million for the years ended December 31, 2016, 2015 and 2014, respectively. The weighted‑average grant date fair value of options granted in the years ended December 31, 2016, 2015 and 2014 was $0.99, $3.80, and $8.61 per share, respectively. The fair value of options that vested during the years ended December 31, 2016, 2015 and 2014 was $6.9 million, $9.5 million, and $6.6 million, respectively. In June 2016, the Company granted stock options to purchase a total of 500,000 shares of common stock to certain employees that vest only upon the achievement of specified performance conditions. The grant date fair value of these options was approximately $445,000. The Company determined that 50% of performance conditions had been achieved during the year ended December 31, 2016. As a result, 250,000 shares vested in October 2016 and the Company recognized stock-based compensation expense related to these awards of approximately $222,000 for the year ended December 31, 2016. The Company determined that the remaining 50% of the performance conditions were not considered probable of achievement as of December 31, 2016 and as a result, has not recognized any stock-based compensation expense related to the remaining unvested awards. At December 31, 2016, there was $4.9 million of total unrecognized compensation cost related to unvested stock options and the Company expects to recognize this cost over a remaining weighted-average period of 1.5 years. Restricted Stock Units A summary of the Company’s RSU activity and related information for the year ended December 31, 2016 is as follows: Shares Weighted-average grant date fair value per share Unvested at December 31, 2015 $ Vested $ Unvested at December 31, 2016 — $ — No restricted stock units were granted during the years ended December 31, 2016, 2015 and 2014. The total fair value of restricted stock units vested during the years ended December 31, 2016, 2015 and 2014 was approximately $65,000, $1.6 million and $2.2 million, respectively. As of December 31, 2016, there was no unrecognized stock‑based compensation expense related to unvested RSUs granted under the 2012 Plan. During 2012, the Company issued a restricted stock unit for 103,306 shares to an employee. The award vests up to 25% per year based on the achievement of stated objectives. The objectives related to 2015 were established on January 8, 2015. In December 2015, the Board of Directors elected not to approve any payment under this award for the year ended December 31, 2015. The Company did not record any stock-based compensation expense for this award during the year ended December 31, 2015. The objectives related to 2014 were established on January 7, 2014 and the objectives were determined to be met on January 8, 2015. The Company recorded $158,000 of stock-based compensation expense for this award during the year ended December 31, 2014 based on the achievement of the stated objectives. During the first quarter of 2013, the Company amended the terms of certain RSUs related to a total of 697,060 shares of common stock to allow for tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs were considered to be liability instruments. As a result of this modification, the Company recorded a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the consolidated statements of operations and comprehensive loss. The Company recorded stock‑based compensation expense equal to the greater of the original grant date fair value of the awards or the settlement date fair value. All RSUs were fully vested as of February 1, 2016. During the year ended December 31, 2016, 2015 and 2014, the Company deposited approximately $5,000, $417,000, and $780,000, respectively, with tax authorities to settle the tax liability for awards that settled during the respective periods. There was no liability related to these awards as of December 31, 2016. The liability related to these awards of approximately $69,000 was recorded as liability classified stock‑based compensation awards on the consolidated balance sheets as of December 31, 2015. Restricted Common Stock In connection with the Company’s formation, the founders purchased an aggregate of 2,857,138 shares of Company’s common stock at fair value on the date of issuance. The shares were issued subject to restricted stock agreements between the Company and each founder, which allow the Company, at its discretion, to repurchase unvested shares if the founder’s relationship with the Company is terminated. Under these agreements, twenty-five percent (25%) of the shares vested immediately and the remaining seventy-five percent (75%) of shares vest ratably in quarterly installments over the subsequent four years. The Company records stock‑based compensation expense for the common stock subject to repurchase, or restricted common stock grants, based on the grant date fair value for employees and the reporting date and upon vesting fair value for non‑employees. The fair value of the award is considered the intrinsic value as of each measurement date. All of the restricted shares were issued at a purchase price equal to the fair value of the common stock on the date of issuance. The Company recorded stock‑based compensation expense associated with restricted common stock grants of $1.7 million for the year ended December 31, 2014. The Company did not record any stock-based compensation expense related to restricted common stock grants in the years ended December 31, 2016 and 2015. No restricted common stock was granted during the years ended December 31, 2016, 2015 and 2014. The total fair value of shares vested during the years ended December 31, 2015 and 2014 was approximately $59,000 and $2.2 million, respectively. All restricted common stock grants were fully vested as of December 31, 2015.

Income taxes

Income taxes	12 Months Ended
	Dec. 31, 2016
Income taxes
Income taxes	8. Income Taxes As of December 31, 2016, the Company had federal and state net operating loss carryforwards of approximately $184.2 million and $182.8 million, respectively, which are available to reduce future taxable income. The Company also had federal and state tax credits of $7.4 million and $1.4 million, respectively, which may be used to offset future tax liabilities. The net operating loss (NOL) and tax credit carryforwards will expire at various dates through 2035. NOL and tax credit carryforwards are subject to review and possible adjustment by the Internal Revenue Service and state tax authorities and may become subject to an annual limitation in the event of certain cumulative changes in the ownership interest of significant stockholders over a three‑year period in excess of 50%, as defined under Sections 382 and 383 of the Internal Revenue Code, as well as similar state provisions. This could limit the amount of tax attributes that can be utilized annually to offset future taxable income or tax liabilities. The amount of the annual limitation is determined based on the value of the Company immediately prior to the ownership change. Subsequent ownership changes may further affect the limitation in future years. A reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations follows: Year Ended December 31, 2016 2015 Income tax benefit using U.S. federal statutory rate % % State tax benefit, net of federal benefit % % Research and development tax credits % % Permanent items % % Change in the valuation allowance % % Other % % — % — % The principal components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ $ Capitalized research and development Research and development credits Stock-based compensation Other Gross deferred tax assets Valuation allowance Net deferred tax asset $ — $ — The Company has recorded a valuation allowance against its deferred tax assets at December 31, 2016 and 2015 because the Company’s management believes that it is more likely than not that these assets will not be fully realized. The increase in the valuation allowance of $13.4 million and $24.2 million in the years ended December 31, 2016 and 2015, respectively, primarily relates to the net loss incurred by the Company. The Company’s reserves related to taxes are based on a determination of whether and how much of a tax benefit taken by the Company in its tax filings or positions is more likely than not to be realized following resolution of any potential contingencies present related to the tax benefit. From inception and through December 31, 2016, the Company had no unrecognized tax benefits or related interest and penalties accrued. The Company has not conducted a study of research and development (R&D) credit carryforwards. This study may result in an adjustment to the Company’s R&D credit carryforwards; however, until a study is completed and any adjustment is known, no amounts are being presented as an uncertain tax position. A full valuation allowance has been provided against the Company’s R&D credits and, if an adjustment is required, this adjustment would be offset by an adjustment to the valuation allowance. Thus, there would be no impact to the consolidated balance sheet or statement of operations if an adjustment were required. The Company would recognize both accrued interest and penalties related to unrecognized benefits in income tax expense. The Company’s uncertain tax positions are related to years that remain subject to examination by relevant tax authorities. Since the Company is in a loss carryforward position, the Company is generally subject to examination by the U.S. federal, state and local income tax authorities for all tax years in which a loss carryforward is available.

Commitments and contingencies

Commitments and contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies
Commitments and Contingencies	9. Commitments and contingencies On April 15, 2014, the Company entered into a lease agreement for approximately 15,197 square feet of office and laboratory space in Needham, Massachusetts. The lease term commenced on April 15, 2014 and expires on September 30, 2019. The Company began using the leased premises as its corporate headquarters and commenced rent payments effective September 22, 2014. The Company agreed to pay an initial annual base rent of approximately $493,000, which base rent increases after every twelve-month period during the lease term to approximately $554,000 for the last twelve-month period. The Company is recording rent expense on a straight-line basis, beginning in April 2014. The Company also received a tenant improvement allowance of approximately $684,000 in connection with the lease. The Company has accounted for the allowance as a lease incentive, which is being recorded as a reduction to rent expense over the lease term. Deferred rent and the lease incentive obligation are included in accrued expenses (current portion) and other liabilities (noncurrent portion) in the consolidated balance sheets. The Company has also agreed to pay its proportionate share of increases in operating expenses and property taxes for the building in which the leased space is located. The Company has provided a security deposit in the form of a letter of credit in the amount of approximately $203,000, which was reduced to approximately $162,000 on April 15, 2016. The amount is included in long term restricted cash on the consolidated balance sheets as of December 31, 2016. The minimum aggregate future lease commitments are as follows (in thousands): 2017 $ 2018 2019 2020 — 2021 — Thereafter — Total $ The Company recorded rent expense of approximately $352,000, $352,000 and $541,000 for the years ended December 31, 2016, 2015 and 2014, respectively. Pursuant to the terms of various agreements, the Company may be required to pay various development, regulatory and commercial milestones. In addition, if any products related to these agreements are approved for sale, the Company may be required to pay significant royalties on future sales. The payment of these amounts, however, is contingent upon the occurrence of various future events, which have a high degree of uncertainty of occurring.

License agreements

License agreements	12 Months Ended
	Dec. 31, 2016
License agreements
License agreements	10. License agreements In November 2016, the Company entered into an amended and restated license agreement with Infinity, under which it acquired an exclusive worldwide license for the research, development, commercialization, and manufacture of products in oncology indications containing duvelisib. In connection with the license agreement, the Company assumed operational and financial responsibility for certain activities that were part of Infinity’s duvelisib program, including the DUO study for patients with relapsed/refractory CLL, and Infinity assumed financial responsibility for the shutdown of certain other clinical studies up to a maximum of $4.5 million. The Company is obligated to use diligent efforts to develop and commercialize a product in an oncology indication containing duvelisib. During the term of the license agreement, Infinity has agreed not to research, develop, manufacture or commercialize duvelisib in any other indication in humans or animals. Pursuant to the terms of the license agreement, the Company is required to make the following payments to Infinity in cash or, at our election, in whole or in part, in shares of our common stock: (i) $6.0 million upon the completion of the DUO study if the results of the DUO study meet certain pre-specified criteria and (ii) $22.0 million upon the approval of a new drug application in the United States or an application for marketing authorization with a regulatory authority outside of the United States for a product in an oncology indication containing duvelisib. For any portion of any of the foregoing payments that it elects to issue in shares of our common stock in lieu of cash, the number of shares of common stock to be issued will be determined by multiplying (1) 1.025 by (2) the number of shares of common stock equal to (a) the amount of the payment to be paid in shares of common stock divided by (b) the average closing price of a share of common stock as quoted on NASDAQ for a twenty day period following the public announcement of the applicable milestone event. The shares of common stock will be issued as unregistered securities, and the Company will have an obligation to promptly file a registration statement with the SEC to register such shares for resale. Any issuance of shares will be subject to the satisfaction of closing conditions, including that all material authorizations, consents, approvals and the like necessary for such issuance shall have been obtained. The Company is also obligated to pay Infinity royalties on worldwide net sales of any products in an oncology indication containing duvelisib ranging from the mid-single digits to the high single-digits. The royalties will expire on a product-by-product and country-by-country basis until the latest to occur of (i) the last-to-expire patent right covering the applicable product in the applicable country, (ii) the last-to-expire patent right covering the manufacture of the applicable product in the country of manufacture of such product, (iii) the expiration of non-patent regulatory exclusivity in such country and (iv) ten years following the first commercial sale of a product in a country, provided that if royalties on net sales for a product in the United States are payable solely on the basis of non-patent regulatory exclusivity, the applicable royalty on net sales for such product in the United States will be reduced by 50%. The royalties are also subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by us if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. In addition to the foregoing, the Company is obligated to pay Infinity an additional royalty of 4% on worldwide net sales of any products in an oncology indication containing duvelisib to cover the reimbursement of research and development costs owed by Infinity to Mundipharma International Corporation Limited (MICL) and Purdue Pharmaceutical Products L.P. (Purdue). Once Infinity has fully reimbursed MICL and Purdue, the royalty obligations will be reduced to 1% of net sales in the United States. These trailing MICL royalties are payable until the later to occur of the last-to-expire of specified patent rights and the expiration of non-patent regulatory exclusivities in a country. Each of the above royalty rates is reduced by 50% on a product-by-product and country-by-country basis if the applicable royalty is payable solely on the basis of non-patent regulatory exclusivity. In addition, the trailing MICL royalties are subject to reduction by 50% of certain third-party royalty payments or patent litigation damages or settlements which might be required to be paid by the us if litigation were to arise, with any such reductions capped at 50% of the amounts otherwise payable during the applicable royalty payment period. The Company evaluated the license agreement with Infinity under ASC Topic 805 , Business Combinations and ASU 2017-01 and concluded that as substantially all of the fair value of the gross assets acquired is concentrated in a single identifiable asset or group of similar assets, the transaction did not meet the requirements to be accounted for as a business combination and therefore was accounted for as an asset acquisition. All consideration to be paid under the License Agreement is contingent in nature and will be recognized when the respective contingency is resolved. On July 11, 2012, the Company entered into a license agreement with Pfizer Inc. (Pfizer), under which Pfizer granted the Company worldwide, exclusive rights to research, develop, manufacture and commercialize products containing certain of Pfizer’s inhibitors of focal adhesion kinase (the FAK Products) for all therapeutic, diagnostic and prophylactic uses in humans. The Company is solely responsible, at its expense, for the clinical development of the FAK Products, which is to be conducted in accordance with an agreed upon development plan. The Company is also responsible for all manufacturing and commercialization activities at its own expense. Pfizer is required to provide the Company with an initial quantity of clinical supply of one of the FAK Products for an agreed upon price. Under the agreement, the Company made a one-time cash payment to Pfizer in the amount of $1.5 million and issued 192,012 shares of its common stock. Pfizer is also eligible to receive up to $2.0 million in developmental milestones and up to an additional $125.0 million based on the successful attainment of regulatory and commercial sales milestones. Pfizer is also eligible to receive high single to mid-double digit royalties on future net sales of the FAK Products. The Company’s royalty obligations with respect to each FAK Product in each country begin on the date of first commercial sale of the FAK Product in that country, and end on the later of 10 years after the date of first commercial sale of the FAK Product in that country or the date of expiration or abandonment of the last claim contained in any issued patent or patent application licensed by Pfizer to the Company that covers the FAK Product in that country. The Company accounted for the license agreement as the licensing of in process research and development with no alternative future use. Under the license agreement with Poniard that the Company entered into in November 2011 relating to VS-4718 and certain other compounds, the Company paid an upfront license fee and agreed to pay Poniard milestone payments upon the achievement of specified development and regulatory milestones. In February 2014, the Company purchased the assets which were the subject of the license agreement with Poniard from Encarta, who had previously purchased these assets in 2013. In consideration for these assets, the Company issued 97,500 shares of common stock, a warrant to purchase 142,857 shares of common stock with an exercise price equal to $17.16 per share and paid $25,000. All existing obligations under the license agreement, including an achieved development milestone and an obligation to issue a warrant, were settled as part of this transaction. The Company incurred $1.2 million of research and development expense in 2014 as a result of this transaction. In connection with the asset purchase agreement, the Company also assumed the rights and obligations under the Scripps License Agreement. Pursuant to the Scripps License Agreement, the Company is obligated to pay Scripps potential product development milestone payments of up to an aggregate of $3.0 million upon the achievement of specified development and regulatory milestones. In addition, the Company is obligated to pay Scripps low-single digit royalties as a percentage of net sales of licensed products, subject to adjustments in certain circumstances. The Company’s obligation to pay royalties on net sales is on a country-by-country basis.

Employee benefit plan

Employee benefit plan	12 Months Ended
	Dec. 31, 2016
Employee benefit plan
Employee benefit plan	11. Employee benefit plan In June 2011, the Company adopted a 401(k) retirement and savings plan (the 401(k) Plan) covering all employees. The 401(k) Plan allows employees to make pre‑tax or post‑tax contributions up to the maximum allowable amount set by the Internal Revenue Service. Under the 401(k) Plan, the Company may make discretionary contributions as approved by the board of directors. The Company made approximate contributions to the 401(k) Plan of $162,000, $295,000 and $219,000 for the years ended December 31, 2016, 2015 and 2014, respectively.

Reduction in force

Reduction in force	12 Months Ended
	Dec. 31, 2016
Reduction in force
Reduction in force	12. Reduction in force In October 2015, the Company announced a reduction of workforce by approximately 50% to 20 full time employees. All affected employees received severance pay and outplacement assistance. As a result of the reduction in force and associated costs, the Company paid one-time severance and related costs of $1.1 million. Of these one-time severance and related costs, approximately $713,000 and approximately $349,000 was paid during the years ended December 31, 2016 and 2015, respectively.

Quarterly financial information

Quarterly financial information (unaudited, in thousands, except per share data)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information (unaudited, in thousands, except per share data)
Quarterly Financial Information	13. Quarterly financial information (unaudited, in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2016 2016 2016 2016 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2015 2015 2015 2015 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a)(b) (b) (b) (a) In January 2015, the Company closed a public offering in which it sold 8,337,500 shares of its common stock at a price of $6.50 per share, including 1,087,500 shares issued pursuant to the exercise of the underwriters’ option to purchase additional shares, which resulted in net proceeds of $50.9 million. (b) In the first, second and third quarters of 2015, the Company sold 470,309, 690,370 and 28,800 shares of its common stock under the Company’s at-the-market equity offering program, which resulted in net proceeds of $4.4 million, $6.2 million and approximately $250,000, respectively

Subsequent events

Subsequent events	12 Months Ended
	Dec. 31, 2016
Subsequent Events.
Subsequent Events	14. Subsequent events The Company reviews all activity subsequent to year end but prior to the issuance of the consolidated financial statements for events that could require disclosure or that could impact the carrying value of assets or liabilities as of the consolidated balance sheets date. The Company is not aware of any material subsequent events other than the following: On March 21, 2017 (Closing Date), Verastem, Inc. (Borrower) entered into a term loan facility of up to $25.0 million (Term Loan) with Hercules Capital, Inc., a Maryland corporation (Hercules), the proceeds of which will be used for its ongoing research and development programs and for general corporate purposes. The Term Loan is governed by a loan and security agreement, dated March 21, 2017 (Loan Agreement), which provides for up to four separate advances. The first tranche of $2.5 million was drawn on the Closing Date. The second tranche of $2.5 million and the third tranche of $5.0 million may be drawn, at the Borrower’s option but subject to the Borrower receiving favorable data from its ongoing Phase III clinical study evaluating the safety and efficacy of duvelisib in patients with relapsed/refractory chronic leukemia or small lymphocytic lymphoma on or prior to September 20, 2017 (Milestone Event), during the period beginning on the Closing Date and ending on the earliest to occur of the date that is 90 days after the Milestone Event and December 20, 2017. The fourth tranche of $15.0 million may be drawn, at the Borrower’s option and at the sole discretion of Hercules, on or prior to June 30, 2018. The Term Loan will mature on December 1, 2020 (Loan Maturity Date). Each advance accrues interest at a floating per annum rate equal to the greater of either (a) 10.5% or (b) the lesser of (i) 12.75% and (ii) the sum of (x) 10.5% plus (y) (A) the prime rate minus (B) 4.5%. The Term Loan provides for interest-only payments until November 1, 2018. The interest-only period may be extended to May 1, 2019 if the Borrower obtains minimum cash proceeds of $20.0 million from a sale of equity securities or subordinated debt and/or ongoing commercial partnerships. Thereafter, amortization payments will be payable monthly in twenty-six installments (or, if the period requiring interest-only payments has been extended to May 1, 2019, in twenty installments) of principal and interest (subject to recalculation upon a change in prime rates). Any advance may be prepaid in whole or in part upon seven business days’ prior written notice to Hercules, subject to a prepayment charge of 3.0%, if such advance is prepaid in any of the first twelve (12) months following the Closing Date, 2.0%, if such advance is prepaid after twelve (12) months following the Closing Date but on or prior to twenty-four (24) months following the Closing Date, and 1.0% thereafter. In addition, a final payment equal to 4.5% of the greater of (a) $5.0 million and (b) the total principal amount of the Term Loan extended by Hercules which is due on the Loan Maturity Date, or such earlier date specified in the Loan Agreement. Amounts outstanding during an event of default shall be payable on demand and shall accrue interest at an additional rate of 5.0% per annum of the past due amount outstanding. The Term Loan is secured by a lien on substantially all of the assets of the Borrower, other than intellectual property and contains customary covenants and representations, including a liquidity covenant, financial reporting covenant and limitations on dividends, indebtedness, collateral, investments, distributions, transfers, mergers or acquisitions, taxes, corporate changes, deposit accounts, and subsidiaries. The events of default under the Loan Agreement include, without limitation, and subject to customary grace periods, (1) the Borrower’s failure to make any payments of principal or interest under the Loan Agreement, promissory notes or other loan documents, (2) the Borrower’s breach or default in the performance of any covenant under the Loan Agreement, (3) the Borrower making a false or misleading representation or warranty in any material respect, (4) the Borrower’s insolvency or bankruptcy, (5) certain attachments or judgments on the Borrower’s assets, or (6) the occurrence of any material default under certain agreements or obligations of the Borrower involving indebtedness, or (7) the occurrence of a material adverse effect. If an event of default occurs, Hercules is entitled to take enforcement action, including acceleration of amounts due under the Loan Agreement.

Significant accounting polici22

Significant accounting policies (Policies)	12 Months Ended
	Dec. 31, 2016
Significant accounting policies.
Basis of consolidation	Basis of consolidation The consolidated financial statements include the accounts of Verastem Securities Company, a wholly owned subsidiary of the Company. All financial information presented has been consolidated and includes the accounts of the Company and its wholly owned subsidiary. All intercompany balances and transactions have been eliminated in consolidation.
Use of estimates	Use of estimates The preparation of the Company’s financial statements in conformity with U.S. generally accepted accounting principles requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. On an ongoing basis, management evaluates its estimates, including estimates related to accruals and stock‑based compensation expense. The Company bases its estimates on historical experience and other market‑specific or other relevant assumptions that it believes to be reasonable. Actual results could differ from such estimates.
Segment and geographic information	Segment and geographic information Operating segments are defined as components of an enterprise about which separate discrete information is available and regularly reviewed by the chief operating decision maker, or decision‑making group, in deciding how to allocate resources and in assessing performance. The Company views its operations and manages its business in one operating segment, which is the business of developing drugs for the treatment of cancer. All material long-lived assets of the Company reside in the United States.
Cash and cash equivalents	Cash and cash equivalents The Company considers all highly liquid investments with an original or remaining maturity of three months or less at the date of purchase to be cash equivalents. Cash equivalents consist of a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies. Cash equivalents are reported at fair value.
Fair value of financial instruments	Fair value of financial instruments The Company determines the fair value of its financial instruments based upon the fair value hierarchy, which prioritizes valuation inputs based on the observable nature of those inputs. The fair value hierarchy applies only to the valuation inputs used in determining the reported fair value of the investments and is not a measure of the investment credit quality. The hierarchy defines three levels of valuation inputs: Level 1 inputs Quoted prices in active markets for identical assets or liabilities that the Company can access at the measurement date. Level 2 inputs Inputs other than quoted prices included within Level 1 that are observable for the asset or liability, either directly or indirectly. Level 3 inputs Unobservable inputs that reflect the Company’s own assumptions about the assumptions market participants would use in pricing the asset or liability. The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — December 31, 2015 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — Financial liabilities Liability classified stock-based compensation awards $ $ $ — $ — Total financial liabilities $ $ $ — $ — These investments and cash equivalents have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third party pricing services or other market observable data. The pricing services utilize industry standard valuation models, including both income and market based approaches and observable market inputs to determine value. These observable market inputs include reportable trades, benchmark yields, credit spreads, broker/dealer quotes, bids, offers, current spot rates and other industry and economic events. The Company validates the prices provided by third party pricing services by reviewing their pricing methods and matrices, obtaining market values from other pricing sources, analyzing pricing data in certain instances and confirming that the relevant markets are active. After completing its validation procedures, the Company did not adjust or override any fair value measurements provided by the pricing services as of December 31, 2016 and 2015. The Company’s liability classified stock-based compensation awards were comprised of restricted stock units (RSUs) that allowed for greater than minimum statutory tax withholdings. These awards were valued based on the fair value of the Company’s common stock underlying the awards, which is traded on an active market. During the first quarter of 2013, the Company amended the terms of certain RSUs to allow for cash tax withholdings greater than the minimum required statutory withholding amount. As a result of this change in the terms of the awards, the outstanding RSUs were considered to be liability instruments. As a result of this modification, the Company recorded a liability for the fair value of the awards as of each reporting date with the change in fair value recorded through the statement of operations. The Company recorded stock-based compensation expense equal to the greater of the original grant date fair value of the awards or the settlement date fair value. All such RSUs were fully vested as of February 1, 2016. During the years ended December 31, 2016 and 2015, the Company made approximate deposits to the taxing authorities of $5,000 and $417,000, respectively, to settle the tax liability for awards that settled during such periods.
Investments	Investments Investments and cash equivalents consist of investments in a U.S. Government money market fund, overnight repurchase agreements collateralized by government agency securities or U.S. Treasury securities, corporate bonds and commercial paper of publicly traded companies that are classified as available‑for‑sale pursuant to Accounting Standards Codification (ASC) Topic 320, Investments—Debt and Equity Securities . The Company classifies investments available to fund current operations as current assets on its consolidated balance sheets. Investments are classified as long‑term assets on the consolidated balance sheets if (i) the Company has the intent and ability to hold the investments for a period of at least one year and (ii) the contractual maturity date of the investments is greater than one year. Investments are carried at fair value with unrealized gains and losses included as a component of accumulated other comprehensive income (loss), which is a separate component of stockholders’ equity (deficit), until such gains and losses are realized. The fair value of these securities is based on quoted prices for identical or similar assets. If a decline in the fair value is considered other‑than‑temporary, based on available evidence, the unrealized loss is transferred from other comprehensive loss to the consolidated statements of operations and comprehensive loss. The Company reviews investments for other‑than‑temporary impairment whenever the fair value of an investment is less than the amortized cost and evidence indicates that an investment’s carrying amount is not recoverable within a reasonable period of time. To determine whether an impairment is other‑than‑temporary, the Company considers the intent to sell, or whether it is more likely than not that the Company will be required to sell, the investment before recovery of the investment’s amortized cost basis. Evidence considered in this assessment includes reasons for the impairment, compliance with the Company’s investment policy, the severity and the duration of the impairment and changes in value subsequent to year end. As of December 31, 2016 and 2015, there were no investments with a fair value that was significantly lower than the amortized cost basis or any investments that had been in an unrealized loss position for a significant period. There were no other‑than‑temporary declines in fair value of short‑term investments for the years ended December 31, 2016, 2015 and 2014. Realized gains and losses are determined using the specific identification method and are included in interest income in the consolidated statements of operations and comprehensive loss. There were no realized gains or losses recognized for the years ended December 31, 2016, 2015 and 2014. Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Overnight repurchase agreements $ — $ — Total cash and cash equivalents $ $ — $ — $ Investments: Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $ December 31, 2015 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Government-sponsored enterprise securities (original maturities within 90 days) — — Corporate bonds and commercial paper (original maturities within 90 days) — — Total cash and cash equivalents $ $ — $ — $ Investments: Government-sponsored enterprise securities (due within 1 year) $ $ $ — $ Treasury securities (due within 1 year) — — Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $
Concentrations of credit risk and off-balance sheet risk	Concentrations of credit risk and off‑balance sheet risk Cash and cash equivalents and investments are financial instruments that potentially subject the Company to concentrations of credit risk. The Company mitigates this risk by maintaining its cash and cash equivalents and investments with high quality, accredited financial institutions. The management of the Company’s investments is not discretionary on the part of these financial institutions. As of December 31, 2016, the Company’s cash, cash equivalents and investments were deposited at two financial institutions and it has no significant off‑balance sheet concentrations of credit risk, such as foreign currency exchange contracts, option contracts or other hedging arrangements.
Property and equipment	Property and equipment Property and equipment consists of laboratory equipment, office furniture, computer equipment and leasehold improvements. Expenditures for repairs and maintenance are recorded to expense as incurred, whereas major betterments are capitalized as additions to property and equipment. Depreciation and amortization is calculated using the straight‑line method over the following estimated useful lives of the assets: Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold Improvements Lesser of useful life or life of lease Upon retirement or sale, the cost of the disposed asset and the related accumulated depreciation are removed from the accounts and any resulting gain or loss is recognized. The Company reviews its long‑lived assets for impairment whenever events or changes in business circumstances indicate that the carrying value of assets may not be recoverable. Recoverability is measured by comparison of the asset’s book value to future net undiscounted cash flows that the assets are expected to generate. If such assets are considered to be impaired, the impairment to be recognized is measured by the amount by which the book value of the assets exceed their fair value, which is measured based on the projected discounted future net cash flows arising from the assets. No material impairment losses have been recorded through December 31, 2016.
Other assets	Other assets Pursuant to the license agreement between the Company and Infinity Pharmaceuticals, Inc. ( Infinity ) amended and restated on November 1, 2016, effective as of October 29, 2016 (the License Agreement), the Company assumed the rights to the remaining balance of certain prepaid amounts as of December 31, 2016 on contracts with contract research organizations (CROs). The License Agreement also requires the Company to reimburse Infinity for these prepaid CRO expenses. The prepaid CRO expenses and corresponding liability of approximately $755,000 are recorded as other assets and accrued expenses on the consolidated balance sheets as of December 31, 2016.
Research and development costs	Research and development costs The Company expenses research and development costs to operations as incurred. Research and development expenses consist of: · employee‑related expenses, including salaries, benefits, travel and stock‑based compensation expense; · external research and development expenses incurred under arrangements with third parties, such as CROs, clinical trial sites, manufacturing organizations and consultants, including the scientific advisory board; · license fees; and · facilities, depreciation and other expenses, which include direct and allocated expenses for rent and maintenance of facilities, depreciation of equipment, and laboratory supplies. The Company accounts for nonrefundable advance payments for goods and services that will be used in future research and development activities as expenses when the services have been performed or when the goods have been received rather than when the payment is made.
Stock-based compensation	Stock‑based compensation The Company expenses the fair value of employee stock-based awards over the requisite service period, which typically is the vesting period. Compensation expense is measured using the fair value of the award at the grant date, net of estimated forfeitures, and is adjusted annually to reflect actual forfeitures. Awards subject to performance based vesting requirements are expensed utilizing an accelerated attribution model if achievement of the performance criteria is determined to be probable. The grant date fair value of employee stock options is estimated using the Black‑Scholes option pricing model that takes into account the fair value of its common stock, the exercise price, the expected life of the option, the expected volatility of its common stock, expected dividends on its common stock, and the risk-free interest rate over the expected life of the option. The Company uses the simplified method described in the Securities and Exchange Commission Staff Accounting Bulletin Topic 14.D.2 to calculate the expected term as it does not have sufficient historical exercise data to provide a reasonable basis upon which to estimate the expected term for options granted to employees. The expected term is applied to the stock option grant group as a whole, as the Company does not expect substantially different exercise or post‑vesting termination behavior among its employee population. The computation of expected volatility is based on the historical volatility of five companies equally weighted, including the Company and a representative group of four public biotechnology and life sciences companies with similar characteristics to the Company, including similar stage of product development and therapeutic focus. The risk‑free interest rate is based on a treasury instrument whose term is consistent with the expected term of the stock options. Management assesses expected forfeitures based on the experience of the Company coupled with comparison to data from the representative group of companies and recognizes compensation costs only for those equity awards expected to vest. Stock‑based awards issued to nonemployees, including directors for non‑board related services, are accounted for based on the fair value of such services received or of the equity instruments issued, whichever is more reliably measured. Stock option awards to non-employees are revalued at each reporting date and upon vesting using the Black‑Scholes option pricing model and are expensed on a straight‑line basis over the vesting period. Stock‑based compensation awards which allowed for greater than the minimum statutory tax withholdings were classified as liabilities. These awards were revalued at each reporting date and were expensed on a straight‑line basis over the vesting period. Upon settlement, the awards were revalued and the amounts were reclassified to additional paid‑in capital. Shares were withheld to cover the tax withholding and amounts paid to settle the tax liability were recorded as a reduction of additional paid‑in capital.
Income taxes	Income taxes The Company accounts for income taxes under the asset and liability method. Deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial statement carrying amounts of existing assets and liabilities and their respective tax bases using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Tax benefits are recognized when it is more likely than not that a tax position will be sustained during an audit. Deferred tax assets are reduced by a valuation allowance if current evidence indicates that it is considered more likely than not that these benefits will not be realized.
Net loss per share	Net loss per share Basic and diluted net loss per common share is calculated by dividing net loss applicable to common stockholders by the weighted‑average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company’s potentially dilutive shares, which include outstanding stock options, restricted stock units, unvested restricted stock and the warrant issued in 2014 are considered to be common stock equivalents and are only included in the calculation of diluted net loss per share when their effect is dilutive. All potentially dilutive securities were excluded from the calculation of diluted net loss per share as the securities were anti‑dilutive for all periods presented. The following potentially dilutive securities were excluded from the calculation of diluted net loss per share due to their anti‑dilutive effect: Year Ended December 31, 2016 2015 2014 Outstanding stock options Outstanding warrants Unvested restricted stock units — Unvested restricted stock — —
Recent Accounting Pronouncements	Recently Issued Accounting Standards Updates In November 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash. ASU 2016-18 requires that a statement of cash flows explain the change during the period in the total of cash, cash equivalents and amounts generally described as restricted cash or restricted cash equivalents. Amounts generally described as restricted cash and restricted cash equivalents should be included with cash and cash equivalents when reconciling the beginning-of-period and end-of-period total amounts shown on the statement of cash flows. ASU 2016-18 is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In October 2016, the FASB issued ASU 2016-17, Consolidation (Topic 810): Interests Held through Related Parties That Are under Common Control . ASU 2016-17 updates ASU 2015-02. Under the amendments, a single decision maker is not required to consider indirect interests held through related parties that are under common control with the single decision maker to be the equivalent of direct interests in their entirety. Instead, a single decision maker is required to include those interests on a proportionate basis consistent with indirect interests held through other related parties. ASU 2016-17 is effective for annual and interim periods beginning after December 15, 2016, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In August 2016, FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments. ASU 2016-15 adds or clarifies guidance on the classification of certain cash receipts and payments in the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2017, with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting . ASU 2016-09 simplifies the accounting for share-based compensation arrangements, including the income tax impact and classification on the statement of cash flows. The standard is effective for annual and interim periods beginning after December 15, 2016 with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which supersedes the guidance under FASB ASC Topic 840, Leases , resulting in the creation of FASB ASC Topic 842, Leases. ASU 2016-02 requires lessees to recognize in the statement of financial position a liability to make lease payments and a right-of-use asset representing its right to use the underlying asset for the lease term for both finance and operating leases. The guidance also eliminates the current real estate-specific provisions for all entities. ASU 2016-02 is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018 with early adoption permitted. The Company has not chosen to early adopt this standard and is currently evaluating the impact the adoption will have on its consolidated financial statements and related disclosures. Recently Adopted Accounting Standards Updates In January 2017, the FASB issued ASU 2017-01, Business Combinations (Topic 805): Clarifying the Definition of a Business. ASU 2017-01 clarifies the definition of a business, provides a screen to determine when a set of assets is not a business and narrows the definition of the term output. ASU 2017-01 is effective for the interim and annual periods after December 15, 2016. Early adoption is permitted. The Company has elected to early adopt ASU 2017-01 and to apply it to the November 2016 amended and restated license agreement with Infinity, under which it acquired an exclusive worldwide license for the research, development, commercialization, and manufacture of products in oncology indications containing duvelisib. In August 2014, the FASB issued ASU 2014-15, Presentation of Financial Statements - Going Concern: Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern (Subtopic 205-40). ASU 2014-15 requires management to assess an entity’s ability to continue as a going concern every reporting period, and provide certain disclosures if management has substantial doubt about the entity’s ability to operate as a going concern, or an express statement if not, by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. ASU 2014-15 is effective for the interim and annual periods after December 15, 2016. Early adoption is permitted. The Company adopted ASU 2014-15 effective October 1, 2016. The Company has evaluated the impact of the adoption of ASU 2014-15 on its year ended December 31, 2016 consolidated financial statements and determined that there is not substantial doubt about the Company’s ability to continue as a going concern for at least one year from the issuance of the December 31, 2016 consolidated financial statements.

Significant accounting polici23

Significant accounting policies (Tables)	12 Months Ended
	Dec. 31, 2016
Significant accounting policies.
Schedule of information about financial assets and liabilities measured at fair value	The following table presents information about the Company’s financial instruments that are measured at fair value on a recurring basis (in thousands): December 31, 2016 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — December 31, 2015 Description Total Level 1 Level 2 Level 3 Financial assets Cash equivalents $ $ $ $ — Short-term investments — — Total financial assets $ $ $ $ — Financial liabilities Liability classified stock-based compensation awards $ $ $ — $ — Total financial liabilities $ $ $ — $ —
Schedule of cash, cash equivalents and investments	Cash, cash equivalents and investments consist of the following (in thousands): December 31, 2016 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Overnight repurchase agreements $ — $ — Total cash and cash equivalents $ $ — $ — $ Investments: Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $ December 31, 2015 Gross Gross Amortized Unrealized Unrealized Fair Cost Gains Losses Value Cash and cash equivalents: Cash and money market accounts $ $ — $ — $ Government-sponsored enterprise securities (original maturities within 90 days) — — Corporate bonds and commercial paper (original maturities within 90 days) — — Total cash and cash equivalents $ $ — $ — $ Investments: Government-sponsored enterprise securities (due within 1 year) $ $ $ — $ Treasury securities (due within 1 year) — — Corporate bonds and commercial paper (due within 1 year) Total investments $ $ $ $ Total cash, cash equivalents, and investments $ $ $ $
Schedule of estimated useful lives of the assets	Laboratory equipment 5 years Furniture 5 years Computer equipment 3 years Leasehold Improvements Lesser of useful life or life of lease
Schedule of potentially anti-dilutive securities excluded from calculation of diluted net loss per share	Year Ended December 31, 2016 2015 2014 Outstanding stock options Outstanding warrants Unvested restricted stock units — Unvested restricted stock — —

Property and equipment (Tables)

Property and equipment (Tables)	12 Months Ended
	Dec. 31, 2016
Property and equipment
Schedule of property equipment and related accumulated depreciation	Property and equipment and related accumulated depreciation are as follows (in thousands): December 31, December 31, 2016 2015 Leasehold improvements $ $ Laboratory equipment Furniture and fixtures Computer equipment Less: accumulated depreciation $ $

Prepaid expenses and other cu25

Prepaid expenses and other current assets (Tables)	12 Months Ended
	Dec. 31, 2016
Prepaid expenses and other current assets
Schedule of prepaid expenses and other current assets	Prepaid expenses and other current assets consist of the following (in thousands): December 31, December 31, 2016 2015 Interest receivable $ $ Prepaid contract research organization costs Prepaid insurance Prepaid other $ $

Accrued expenses (Tables)

Accrued expenses (Tables)	12 Months Ended
	Dec. 31, 2016
Accrued expenses
Schedule of accrued expenses	Accrued expenses consist of the following (in thousands): December 31, 2016 December 31, 2015 Contract research organization costs $ $ Compensation and related benefits Consulting fees — Professional fees Deferred rent Other $ $

Common stock (Tables)

Common stock (Tables)	12 Months Ended
	Dec. 31, 2016
Common stock.
Schedule of shares of common stock reserved for the issuance of common stock for vested restricted stock units and the exercise of stock options	As of December 31, 2016 and 2015, the Company had reserved the following shares of common stock for the issuance of common stock for vested restricted stock units, the exercise of stock options, and an outstanding warrant (in thousands): December 31, December 31, 2016 2015 Shares reserved under equity compensation plans Shares reserved for inducement grants Shares reserved for outstanding warrants

Stock-based compensation (Table

Stock-based compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Stock-based compensation
Schedule of stock-based compensation expense as reflected in the Company's consolidated statements of operations and comprehensive loss	Stock‑based compensation expense as reflected in the Company’s consolidated statements of operations and comprehensive loss was as follows (in thousands): Year Ended December 31, 2016 2015 2014 Research and development $ $ $ General and administrative Total stock-based compensation expense $ $ $
Summary of stock option activity and related information	Weighted-average Weighted-average remaining Aggregate exercise price per contractual term intrinsic value Shares share (years) (in thousands) Outstanding at December 31, 2015 $ $ Granted $ Exercised $ Forfeited/cancelled $ Outstanding at December 31, 2016 $ $ Vested at December 31, 2016 $ $ Vested and expected to vest at December 31, 2016(1) $ $ (1) This represents the number of vested options as of December 31, 2016, plus the number of unvested options expected to vest as of December 31, 2016, based on the unvested options at December 31, 2016, adjusted for the estimated forfeiture rate.
Schedule of assumptions used to estimate fair value of each stock option on grant date	Year Ended December 31, 2016 2015 2014 Risk-free interest rate % % % Volatility % % % Dividend yield — — — Expected term (years)
Schedule of restricted stock units	Shares Weighted-average grant date fair value per share Unvested at December 31, 2015 $ Vested $ Unvested at December 31, 2016 — $ —

Income taxes (Tables)

Income taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income taxes
Schedule of reconciliation of income taxes computed using the U.S. federal statutory rate to that reflected in operations	Year Ended December 31, 2016 2015 Income tax benefit using U.S. federal statutory rate % % State tax benefit, net of federal benefit % % Research and development tax credits % % Permanent items % % Change in the valuation allowance % % Other % % — % — %
Schedule of principal components of deferred tax assets	The principal components of the Company’s deferred tax assets are as follows (in thousands): December 31, 2016 2015 Deferred tax assets: Net operating loss carryforwards $ $ Capitalized research and development Research and development credits Stock-based compensation Other Gross deferred tax assets Valuation allowance Net deferred tax asset $ — $ —

Commitments and contingencies (

Commitments and contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies
Schedule of minimum aggregate future lease commitments	The minimum aggregate future lease commitments are as follows (in thousands): 2017 $ 2018 2019 2020 — 2021 — Thereafter — Total $

Quarterly financial informati31

Quarterly financial information (unaudited, in thousands, except per share data) (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information (unaudited, in thousands, except per share data)
Schedule of Quarterly Financial Information	Quarterly financial information (unaudited, in thousands, except per share data) First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2016 2016 2016 2016 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted First Quarter Second Quarter Third Quarter Fourth Quarter Ended Ended Ended Ended March 31, June 30, September 30, December 31, 2015 2015 2015 2015 Operating expenses: Research and development $ $ $ $ General and administrative Total operating expenses Loss from operations Interest income Net loss $ $ $ $ Net loss per share —basic and diluted $ $ $ $ Weighted-average number of common shares used in net loss per share —basic and diluted (a)(b) (b) (b) (a) In January 2015, the Company closed a public offering in which it sold 8,337,500 shares of its common stock at a price of $6.50 per share, including 1,087,500 shares issued pursuant to the exercise of the underwriters’ option to purchase additional shares, which resulted in net proceeds of $50.9 million. (b) In the first, second and third quarters of 2015, the Company sold 470,309, 690,370 and 28,800 shares of its common stock under the Company’s at-the-market equity offering program, which resulted in net proceeds of $4.4 million, $6.2 million and approximately $250,000, respectively

Nature of business (Details)

Nature of business (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Nature of business
Cash, cash equivalents, and investments	$ 80,897	$ 110,258
Deficit accumulated during the development stage	$ 235,323	$ 198,883
Substantial doubt about the ability to continue as a going concern	false

Significant accounting polici33

Significant accounting policies - Segment Information and Fair Value Financial Instruments (Details)	12 Months Ended
	Dec. 31, 2016USD ($)item	Dec. 31, 2015USD ($)
Segment and geographic information
Number of operating segments | item	1
Financial assets
Cash equivalents	$ 32,349,000	$ 24,870,000
Short-term investments	48,548,000	85,388,000
Financial liabilities
Liability classified stock-based compensation awards	0	69,000
Recurring basis | Total
Financial assets
Cash equivalents	30,540,000	23,036,000
Short-term investments	48,548,000	85,388,000
Total financial assets	79,088,000	108,424,000
Financial liabilities
Liability classified stock-based compensation awards		69,000
Total financial liabilities		69,000
Recurring basis | Level 1
Financial assets
Cash equivalents	20,540,000	11,464,000
Total financial assets	20,540,000	11,464,000
Financial liabilities
Liability classified stock-based compensation awards		69,000
Total financial liabilities		69,000
Recurring basis | Level 2
Financial assets
Cash equivalents	10,000,000	11,572,000
Short-term investments	48,548,000	85,388,000
Total financial assets	$ 58,548,000	$ 96,960,000

Significant accounting polici34

Significant accounting policies - Fair value, Cash, Cash Equivalents (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Amortized cost
Cash and cash equivalents, Amortized cost	$ 32,349	$ 24,870	$ 33,901	$ 18,889
Investments, Amortized Cost	48,519	85,345
Total cash, cash equivalents, and investments, Amortized Cost	80,868	110,215
Gross unrealized gains
Gross unrealized gains	53	62
Gross unrealized losses
Gross unrealized losses	(24)	(19)
Fair value
Cash and cash equivalents, Fair value	32,349	24,870
Investments, Fair Value	48,548	85,388
Total cash, cash equivalents, and investments, Fair Value	$ 80,897	$ 110,258
Government-sponsored enterprise securities
Investments
Maturity period, investments		1 year
Amortized cost
Due within 1 year		$ 11,932
Gross unrealized gains
Gross unrealized gains		5
Fair value
Due within 1 year		$ 11,937
Treasury securities
Investments
Maturity period, investments		1 year
Amortized cost
Due within 1 year		$ 1,005
Fair value
Due within 1 year		$ 1,005
Corporate bonds and commercial paper
Investments
Maturity period, investments	1 year	1 year
Amortized cost
Due within 1 year	$ 48,519	$ 72,408
Gross unrealized gains
Gross unrealized gains	53	57
Gross unrealized losses
Gross unrealized losses	(24)	(19)
Fair value
Due within 1 year	48,548	72,446
Cash and money market accounts
Amortized cost
Cash and cash equivalents, Amortized cost	22,349	13,298
Fair value
Cash and cash equivalents, Fair value	22,349	$ 13,298
Overnight repurchase agreements
Amortized cost
Cash and cash equivalents, Amortized cost	10,000
Fair value
Cash and cash equivalents, Fair value	$ 10,000
Government-sponsored enterprise securities
Investments
Original maturity period, cash and cash equivalents		90 days
Amortized cost
Cash and cash equivalents, Amortized cost		$ 2,000
Fair value
Cash and cash equivalents, Fair value		$ 2,000
Corporate bonds and commercial paper
Investments
Original maturity period, cash and cash equivalents		90 days
Amortized cost
Cash and cash equivalents, Amortized cost		$ 9,572
Fair value
Cash and cash equivalents, Fair value		$ 9,572

Significant accounting polici35

Significant accounting policies - Tax Withholding (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant accounting policies.
Cash used to settle tax on restricted stock liability awards	$ 5	$ 417	$ 780

Significant accounting polici36

Significant accounting policies - Investments (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Significant accounting policies.
Charges for other-than-temporary declines in fair value of short-term or long-term investments	$ 0	$ 0	$ 0
Realized gains or losses on investments	$ 0	$ 0	$ 0

Significant accounting polici37

Significant accounting policies - Concentration of Credit Risk and Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2016USD ($)item
Concentrations of credit risk and off-balance sheet risk
Number of financial institutions in which cash, cash equivalents and investments were deposited	2
Other assets
Prepaid CRO Expenses | $	$ 755,000
Share-based compensation
Number of companies expected volatility is based	5
Number of companies with similar characteristics to the Company included in computation	4
Laboratory equipment
Property and equipment
Estimated useful lives	5 years
Furniture and fixtures
Property and equipment
Estimated useful lives	5 years
Computer equipment
Property and equipment
Estimated useful lives	3 years

Significant accounting polici38

Significant accounting policies - Net Loss Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	5,991,327	5,586,738	4,651,039
Outstanding stock options
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	5,848,470	5,390,130	4,206,440
Outstanding warrants
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)	142,857	142,857	142,857
Restricted Stock Units
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)		53,751	293,747
Restricted Common Stock
Net loss per share
Potentially anti-dilutive securities excluded from calculation of diluted net loss per share (in shares)			7,995

Property and equipment (Details

Property and equipment (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Property and equipment
Property and equipment, gross	$ 3,616	$ 3,577
Less: accumulated depreciation	(2,199)	(1,529)
Property and equipment, net	1,417	2,048
Depreciation and amortization	670	754	$ 427
Leasehold improvements
Property and equipment
Property and equipment, gross	2,104	2,104
Laboratory equipment
Property and equipment
Property and equipment, gross	908	908
Furniture and fixtures
Property and equipment
Property and equipment, gross	325	325
Computer equipment
Property and equipment
Property and equipment, gross	$ 279	$ 240

Prepaid expenses and other cu40

Prepaid expenses and other current assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Prepaid expenses and other current assets
Interest receivable	$ 204	$ 154
Prepaid contract research organization costs	96	404
Prepaid insurance	65	25
Prepaid other	33	2
Prepaid expenses and other current assets	$ 398	$ 585

Accrued expenses (Details)

Accrued expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Accrued expenses
Contract research organization costs	$ 3,258	$ 3,782
Compensation and related benefits	2,505	1,802
Consulting fees	527
Professional fees	403	260
Deferred rent	175	160
Other	28	94
Accrued expenses	$ 6,896	$ 6,098

Common stock (Details)

Common stock (Details)	1 Months Ended		3 Months Ended			12 Months Ended
	Feb. 28, 2014$ / sharesshares	Dec. 31, 2013USD ($)	Sep. 30, 2015USD ($)shares	Jun. 30, 2015USD ($)shares	Mar. 31, 2015USD ($)shares	Dec. 31, 2016USD ($)Voteshares	Dec. 31, 2015USD ($)shares	Dec. 31, 2014USD ($)
Common stock
Shares reserved for issuance						8,587,000	6,851,000
Number of votes entitled for each share of common stock | Vote						1
At-the-market equity offering program
Proceeds from issuance of common stock | $							$ 63,989,000	$ 9,534,000
Encarta, Inc.
Warrant
Number of shares of common stock in the warrant issued	142,857
Exercise price of shares of common stock in the warrant issued (in dollars per share) | $ / shares	$ 17.16
Expiration period of warrant	3 years
Outstanding warrants
Common stock
Shares reserved for issuance						143,000	143,000
At The Market Equity Offering Program
At-the-market equity offering program
Maximum value of common stock allowed to be sold | $		$ 35,000,000
Number of shares of common stock issued			28,800	690,370	470,309	0	1,189,479
Proceeds from issuance of common stock | $			$ 250,000	$ 6,200,000	$ 4,400,000	$ 0	$ 12,900,000
Inducement Award Program
Common stock
Shares reserved for issuance						1,255,000	750,000
Equity compensation plans
Common stock
Shares reserved for issuance						7,189,000	5,958,000

Stock-based compensation - Stoc

Stock-based compensation - Stock-Based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock-based compensation
Total stock-based compensation expense	$ 6,218	$ 9,684	$ 12,112
Adjustments to additional paid-in capital	6,287	10,085	12,360
Increase (decrease) in stock-based compensation award liability	(69)	(400)	(248)
Research and development
Stock-based compensation
Total stock-based compensation expense	1,073	2,411	3,727
General and administrative
Stock-based compensation
Total stock-based compensation expense	$ 5,145	$ 7,273	$ 8,385

Stock-based compensation - Equi

Stock-based compensation - Equity Plans (Details)	12 Months Ended
	Dec. 31, 2016item
Stock-based compensation
Number of equity compensation plans	2
Outstanding stock options
Stock-based compensation
Expiration term	10 years
Outstanding stock options | One year from vesting
Stock-based compensation
Vesting percentage	25.00%
Vesting period	1 year
Outstanding stock options | Each successive three-month period, thereafter
Stock-based compensation
Vesting percentage	6.25%
Vesting period	3 months

Stock-based compensation - St45

Stock-based compensation - Stock Plans and Activity (Details) - shares	Jan. 01, 2017	Jan. 01, 2016	Jan. 01, 2015	Dec. 31, 2016	Feb. 29, 2012	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2016
Stock-based compensation
Additional number of shares authorized for issuance				580,000
Outstanding stock options
Stock-based compensation
Granted (in shares)						1,913,280
Restricted Stock Units
Stock-based compensation
Granted (in shares)						0	0	0	0
2012 Plan
Stock-based compensation
Number of shares reserved					3,428,571
Additional number of shares authorized for issuance	1,285,714	1,285,714	1,081,045		30,101
Annual increase in number of shares reserved						1,285,714
Percentage of outstanding shares of common stock used to compute annual increase in number of shares reserved						4.00%
2012 Plan | Outstanding stock options
Stock-based compensation
Granted (in shares)						7,874,773
Forfeited (in shares)						2,672,751
2012 Plan | Restricted Stock Units
Stock-based compensation
Granted (in shares)						909,918
Forfeited (in shares)						150,101
Inducement Award Program
Stock-based compensation
Number of shares reserved								750,000
Granted (in shares)						580,000	210,000
Forfeited (in shares)						75,000	75,000
Shares available for future grants				750,000		750,000			750,000

Stock-based compensation - St46

Stock-based compensation - Stock Options (Details) - USD ($)	1 Months Ended	7 Months Ended	12 Months Ended
	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2016
Additional disclosures
Stock-based compensation expense			$ 6,218,000	$ 9,684,000	$ 12,112,000
Outstanding stock options
Shares
Outstanding at the beginning of the period (in shares)			5,390,130
Granted (in shares)			1,913,280
Exercised (in shares)			(1,605)
Forfeited/cancelled (in shares)			(1,453,335)
Outstanding at the end of the period (in shares)		5,848,470	5,848,470	5,390,130
Vested at the end of the period (in shares)		3,444,586	3,444,586
Vested and expected to vest at end of period (in shares)		5,415,064	5,415,064
Weighted-average exercise price per share
Outstanding at the beginning of the period (in dollars per share)			$ 8.71
Granted (in dollars per share)			1.53
Exercised (in dollars per share)			0.28
Forfeited/cancelled (in dollars per share)			8.73
Outstanding at the end of the period (in dollars per share)		$ 6.35	6.35	$ 8.71
Vested at the end of the period (in dollars per share)		7.94	7.94
Vested and expected to vest at end of the period (in dollars per share)		$ 6.70	$ 6.70
Weighted-average remaining contractual term
Outstanding at the end of the period			8 years	8 years 1 month 6 days
Vested at the end of the period			7 years 6 months
Vested and expected to vest at the end of the period			7 years 10 months 24 days
Aggregate intrinsic value
Outstanding at the end of the period (in dollars)		$ 62,000	$ 62,000	$ 175,000
Vested at the end of the period (in dollars)		61,000	61,000
Vested and expected to vest at end of the period (in dollars)		62,000	$ 62,000
Assumptions used to estimate fair value of each stock-based award on the grant date
Risk-free interest rate (as a percent)			1.48%	1.75%	1.99%
Volatility (as a percent)			75.00%	73.00%	81.00%
Expected term			5 years 10 months 24 days	6 years	6 years
Additional disclosures
Stock-based compensation expense			$ 6,100,000	$ 7,900,000	$ 7,800,000
Weighted-average grant date fair value (in dollars per share)			$ 0.99	$ 3.80	$ 8.61
Fair value of vested stock options			$ 6,900,000	$ 9,500,000	$ 6,600,000
Total unrecognized stock-based compensation expense (in dollars)		4,900,000	$ 4,900,000
Weighted-average recognition period			1 year 6 months
Performance shares
Shares
Granted (in shares)	500,000
Vested at the end of the period (in shares)						250,000
Additional disclosures
Stock-based compensation expense		$ 222,000
Grant date fair value of options	$ 445,000
Percentage of performance conditions achieved		50.00%	50.00%
Percentage of performance conditions not considered probable of achievement		50.00%	50.00%

Stock-based compensation - Rest

Stock-based compensation - Restricted Stock (Details) - USD ($)	3 Months Ended	12 Months Ended					24 Months Ended	36 Months Ended
	Sep. 30, 2010	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2016	Dec. 31, 2016	Mar. 31, 2013
Shares
Unvested at the beginning of the period (in shares)		53,751
Vested (in shares)		(53,751)
Unvested at the end of the period (in shares)			53,751
Weighted-average grant date fair value
Unvested at the beginning of the period (in dollars per share)		$ 11
Vested (in dollars per share)		$ 11
Unvested at the end of the period (in dollars per share)			$ 11
Additional disclosures
Stock-based compensation expense		$ 6,218,000	$ 9,684,000	$ 12,112,000
Cash used to settle tax on restricted stock liability awards		5,000	417,000	780,000
Liability classified stock-based compensation awards		$ 0	69,000				$ 0	$ 0
Restricted Common Stock
Additional disclosures
Fair value of shares vested			$ 59,000	2,200,000
Shares issued	2,857,138
Stock-based compensation expense				$ 1,700,000			0
Restricted Common Stock | Vesting Immediately
Additional disclosures
Vesting percentage		25.00%
Restricted Common Stock | Vesting ratably in quarterly installments
Additional disclosures
Vesting percentage		75.00%
Vesting period for quarterly installments		4 years
Restricted Stock Units
Additional disclosures
Granted (in shares)		0	0	0				0
Fair value of shares vested		$ 65,000	$ 1,600,000	$ 2,200,000
Unrecognized stock-based compensation expense		0					$ 0	$ 0
Shares issued						103,306
Vesting percentage per year					25.00%
Stock-based compensation expense				158,000
Unvested RSUs with amended terms									697,060
Cash used to settle tax on restricted stock liability awards		$ 5,000	417,000	$ 780,000
Liability classified stock-based compensation awards			$ 69,000

Income taxes - Operating Loss C

Income taxes - Operating Loss Carryforwards (Details) $ in Millions	Dec. 31, 2016USD ($)
Federal
Operating loss carryforwards
Net operating loss carryforwards	$ 184.2
State
Operating loss carryforwards
Net operating loss carryforwards	$ 182.8

Income taxes - Tax Credits (Det

Income taxes - Tax Credits (Details) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Tax credit carryforwards
Testing period for changes in ownership interest of significant shareholders	3 years
Federal
Tax credit carryforwards
Tax credits	$ 7.4
State
Tax credit carryforwards
Tax credits	$ 1.4

Income taxes - Reconciliation o

Income taxes - Reconciliation of Income Taxes and Deferred Tax Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of income taxes computed using the U.S. federal statutory rate
Income tax benefit using U.S. federal statutory rate (as a percent)	34.00%	34.00%
State tax benefit, net of federal benefit (as a percent)	3.43%	5.91%
Research and development tax credits (as a percent)	4.42%	1.49%
Permanent items (as a percent)	(3.88%)	(3.02%)
Change in the valuation allowance (as a percent)	(36.71%)	(41.90%)
Other (as a percent)	(1.26%)	3.52%
Effective income tax rate (as a percent)	0.00%	0.00%
Deferred tax assets:
Net operating loss carryforwards	$ 72,285,000	$ 61,606,000
Capitalized research and development	1,836,000	1,984,000
Research and development credits	8,298,000	4,087,000
Stock-based compensation	3,083,000	4,401,000
Other	429,000	478,000
Gross deferred tax assets	85,931,000	72,556,000
Valuation allowance	(85,931,000)	(72,556,000)
Additional disclosures
Increase in valuation allowance	13,400,000	$ 24,200,000
Unrecognized tax benefits	0
Interest and penalties accrued related to unrecognized tax benefits	0
Uncertain tax positions	$ 0

Commitments and contingencies51

Commitments and contingencies (Details)	Apr. 15, 2014USD ($)ft²	Dec. 31, 2016USD ($)	Apr. 15, 2016USD ($)	Dec. 31, 2015USD ($)
Operating Leased Assets
Letter of credit secured in connection with the lease, included in restricted cash		$ 162,000		$ 203,000
Office and Laboratory Space in Needham, Massachusetts
Operating Leased Assets
Area of space | ft²	15,197
Initial annual base rent	$ 493,000
Period after which base rent increases	P12M
Base rent for last twelve-month period	$ 554,000
Tenant improvement allowance received	684,000
Letter of credit | Office and Laboratory Space in Needham, Massachusetts
Operating Leased Assets
Security deposit	$ 203,000		$ 162,000

Commitments and contingencies52

Commitments and contingencies (Future Lease Commitments) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Minimum aggregate future lease commitments
2,017	$ 527,000
2,018	542,000
2,019	415,000
Total	1,484,000
Rent expense	$ 352,000	$ 352,000	$ 541,000

License agreements (Details)

License agreements (Details)

Jul. 11, 2012USD ($)itemshares

Nov. 30, 2016USD ($)

Feb. 28, 2014USD ($)$ / sharesshares

Dec. 31, 2016USD ($)

Sep. 30, 2016USD ($)

Jun. 30, 2016USD ($)

Mar. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Sep. 30, 2015USD ($)

Jun. 30, 2015USD ($)

Mar. 31, 2015USD ($)

Dec. 31, 2016USD ($)

Dec. 31, 2015USD ($)

Dec. 31, 2014USD ($)

License agreements

Fair value of common stock issued

$ 11,646,000

Research and development expense

$ 6,892,000

$ 4,216,000

$ 4,492,000

$ 4,179,000

$ 7,688,000

$ 11,304,000

$ 11,045,000

$ 10,528,000

$ 19,779,000

$ 40,565,000

$ 35,448,000

Encarta, Inc.

License agreements

Number of shares of common stock in the warrant issued under the license agreement | shares

142,857

Exercise price of shares of common stock in the warrant issued under the license agreement (in dollars per share) | $ / shares

$ 17.16

Exclusive license agreement | Infinity

License agreements

Maximum exposure by licensor

$ 4,500,000

Payments on completion of D U O Study

6,000,000

Payments on approval of new drug application

$ 22,000,000

Multiplier for issuance of common stock

1.025%

Period for computing average closing price

20 days

Royalty obligations term

10 years

Percentage of reduction in royalty on net sales

50.00%

Deduction in royalty payments as percentage of amount paid to third party

50.00%

Percentage royalty reductions capped

50.00%

Percentage of additional royalty on worldwide net sales

4.00%

Percentage of net sales for royalty obligations in the United States

1.00%

Percentage of reduction of royalty rate on basis of non-patent regulatory exclusivity

50.00%

Exclusive license agreement | PFIZER

License agreements

Royalty obligations term

10 years

Number of products required from licensor for an agreed upon price | item

1

One-time cash payment

$ 1,500,000

Number of shares of common stock issued | shares

192,012

Exclusive license agreement | PFIZER | Maximum

License agreements

Eligible amount payable on developmental milestones to Pfizer

$ 2,000,000

Additional payable on successful attainment of regulatory and commercial sales milestones

$ 125,000,000

Exclusive license agreement | Encarta, Inc.

License agreements

Number of shares of common stock issued | shares

97,500

Number of shares of common stock in the warrant issued under the license agreement | shares

142,857

Exercise price of shares of common stock in the warrant issued under the license agreement (in dollars per share) | $ / shares

$ 17.16

Cash payment under the agreement

$ 25,000

Research and development expense

1,200,000

Exclusive license agreement | Scripps

License agreements

Milestone payments triggered upon the achievement of specified regulatory and commercialization milestones

$ 3,000,000

Employee benefit plan (Details)

Employee benefit plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee benefit plan
Contributions made under 401(k) plan	$ 162,000	$ 295,000	$ 219,000

Reduction in force (Details)

Reduction in force (Details)	1 Months Ended	12 Months Ended	15 Months Ended
	Oct. 31, 2015USD ($)item	Dec. 31, 2016USD ($)	Dec. 31, 2016USD ($)
Restructuring Costs
Severance paid		$ 713,000
Employee Severance
Restructuring Costs
Reduction of workforce (as a percent)	50.00%
Number of full time employees | item	20
Estimated one- time severance and related costs	$ 1,100,000
Severance paid			$ 349,000

Quarterly financial informati56

Quarterly financial information (unaudited, in thousands, except per share data) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Operating expenses:
Research and development	$ 6,892	$ 4,216	$ 4,492	$ 4,179	$ 7,688	$ 11,304	$ 11,045	$ 10,528	$ 19,779	$ 40,565	$ 35,448
General and administrative	4,908	3,843	4,217	4,255	4,273	4,230	4,417	4,714	17,223	17,634	18,159
Total operating expenses	11,800	8,059	8,709	8,434	11,961	15,534	15,462	15,242	37,002	58,199	53,607
Loss from operations	(11,800)	(8,059)	(8,709)	(8,434)	(11,961)	(15,534)	(15,462)	(15,242)	(37,002)	(58,199)	(53,607)
Interest income	145	137	140	140	98	89	85	62	562	334	242
Net loss	$ (11,655)	$ (7,922)	$ (8,569)	$ (8,294)	$ (11,863)	$ (15,445)	$ (15,377)	$ (15,180)	$ (36,440)	$ (57,865)	$ (53,365)
Net loss per share - basic and diluted	$ (0.32)	$ (0.21)	$ (0.23)	$ (0.22)	$ (0.32)	$ (0.42)	$ (0.42)	$ (0.46)	$ (0.99)	$ (1.61)	$ (2.07)
Weighted-average number of common shares used in net loss per share—basic and diluted	36,992,000	36,992,000	36,992,000	36,975,000	36,935,000	36,898,000	36,522,000	33,323,000	36,988,000	35,932,000	25,804,000

Quarterly financial informati57

Quarterly financial information (unaudited, in thousands, except per share data) (Details) - USD ($)	1 Months Ended	3 Months Ended			12 Months Ended
	Jan. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Proceeds from issuance of common stock						$ 63,989,000	$ 9,534,000
Follow-on offering
Number of shares of common stock issued	8,337,500
Share price (in dollars per share)	$ 6.50
Proceeds from issuance of common stock	$ 50,900,000
Underwriters' option
Number of shares of common stock issued	1,087,500
At The Market Equity Offering Program
Number of shares of common stock issued		28,800	690,370	470,309	0	1,189,479
Proceeds from issuance of common stock		$ 250,000	$ 6,200,000	$ 4,400,000	$ 0	$ 12,900,000

Subsequent events (Details)

Subsequent events (Details) - Subsequent events - Term loan $ in Millions	Mar. 21, 2017USD ($)item
Subsequent events
Maximum borrowing capacity	$ 25
Number of separate advances | item	4
Interest rate	10.50%
Minimum cash proceeds to extend interest only payment period	$ 20
Amortization payments, installments | item	26
Number of business days prior written notice for prepayment	7 days
Percentage of total principal amount, as final payment	4.50%
Threshold for final debt payment	$ 5
Additional interest rate in an event of default	5.00%
First tranche drawn on closing date
Subsequent events
Maximum borrowing capacity	$ 2.5
Second tranche
Subsequent events
Maximum borrowing capacity	2.5
Third tranche
Subsequent events
Maximum borrowing capacity	$ 5
Second and third tranches
Subsequent events
Period after milestone event	90 days
Fourth tranche
Subsequent events
Maximum borrowing capacity	$ 15
Interest-only payments extended
Subsequent events
Amortization payments, installments | item	20
Advance prepaid within 12 months following closing date
Subsequent events
Prepayment charge (as a percent)	3.00%
Advance prepaid between 12 months and 24 months following closing date
Subsequent events
Prepayment charge (as a percent)	2.00%
Advance prepaid after 24 months
Subsequent events
Prepayment charge (as a percent)	1.00%
Prime rate
Subsequent events
Basis spread	(4.50%)
Minimum
Subsequent events
Interest rate	10.50%
Maximum
Subsequent events
Interest rate	12.75%