Veracyte (VCYT) 10-K 14 Mar 16 2015 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Mar. 04, 2016	Jun. 30, 2015
Document and Entity Information
Entity Registrant Name	VERACYTE, INC.
Entity Central Index Key	1,384,101
Document Type	10-K
Document Period End Date	Dec. 31, 2015
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	Accelerated Filer
Entity Public Float			$ 151.4
Entity Common Stock, Shares Outstanding		27,854,567
Document Fiscal Year Focus	2,015
Document Fiscal Period Focus	FY

Balance Sheets

Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Current assets:
Cash and cash equivalents	$ 39,084	$ 35,014
Accounts receivable, net of allowance of $117 and $84 as of December 31, 2015 and 2014, respectively	3,503	3,050
Supplies inventory	3,767	3,696
Prepaid expenses and other current assets	1,461	1,218
Deferred tax asset		300
Restricted cash	118	70
Total current assets	47,933	43,348
Property and equipment, net	10,314	4,161
Finite-lived intangible assets, net	15,200
Indefinite-lived intangible assets: in-process research and development		16,000
Goodwill	1,057	1,057
Restricted cash	603	118
Other assets	178	155
Total assets	75,285	64,839
Current liabilities:
Accounts payable	5,085	7,397
Accrued liabilities	8,689	7,851
Deferred Genzyme co-promotion fee	948	1,897
Total current liabilities	14,722	17,145
Long-term debt	5,028	4,923
Deferred tax liability		300
Deferred rent, net of current portion	4,283	149
Deferred Genzyme co-promotion fee, net of current portion		948
Total liabilities	$ 24,033	$ 23,465
Commitments and contingencies
Stockholders' equity:
Preferred stock, $0.001 par value; 5,000,000 shares authorized, no shares issued and outstanding as of December 31, 2015 and December 31, 2014
Common stock, $0.001 par value; 125,000,000 shares authorized, 27,685,291 and 22,523,529 shares issued and outstanding as of December 31, 2015 and 2014, respectively	$ 28	$ 23
Additional paid-in capital	199,950	156,373
Accumulated deficit	(148,726)	(115,022)
Total stockholders' equity	51,252	41,374
Total liabilities and stockholders' equity	$ 75,285	$ 64,839

Balance Sheets (Parenthetical)

Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Balance Sheets
Accounts receivable, allowance (in dollars)	$ 117	$ 84
Preferred stock, par value (in dollars per share)	$ 0.001	$ 0.001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	125,000,000	125,000,000
Common stock, shares issued	27,685,291	22,523,529
Common stock, shares outstanding	27,685,291	22,523,529

Statements of Operations and Co

Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Statements of Operations and Comprehensive Loss
Revenue	$ 49,503	$ 38,190	$ 21,884
Operating expenses:
Cost of revenue	21,497	16,606	12,607
Research and development	12,796	9,804	7,810
Selling and marketing	25,293	21,932	12,540
General and administrative	22,583	18,854	12,100
Intangible asset amortization	800
Total operating expenses	82,969	67,196	45,057
Loss from operations	(33,466)	(29,006)	(23,173)
Interest expense	(378)	(439)	(233)
Other income (expense), net	140	72	(2,174)
Net loss	(33,704)	(29,373)	(25,580)
Comprehensive loss	$ (33,704)	$ (29,373)	$ (25,580)
Net loss per common share, basic and diluted (in dollars per share)	$ (1.30)	$ (1.36)	$ (6.15)
Shares use to compute net loss per common share, basic and diluted (in shares)	25,994,193	21,639,374	4,158,664

Statements of Convertible Prefe

Statements of Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Convertible Preferred Stock.	Series C	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2012	$ 63,372
Balance (in shares) at Dec. 31, 2012	53,084,507
Balance at Dec. 31, 2012			$ 1	$ 1,597	$ (60,069)	$ (58,471)
Balance (in shares) at Dec. 31, 2012			667,684
Increase (Decrease) in Convertible Preferred Stock and Stockholders' Equity (Deficit)
Issuance of Series C convertible preferred stock in June 2013 at $1.89 per share, net of issuance costs of $53		$ 12,997
Issuance of Series C convertible preferred stock in June 2013 at $1.89 per share, net of issuance costs of $53 (in shares)		6,904,761
Extinguishment of the preferred stock liability	$ 2,653
Issuance of common stock on exercise of stock options				552		552
Issuance of common stock on exercise of stock options (in shares)			377,966
Issuance of common stock in initial public offering, net of discounts and commissions of $4,642 and issuance costs of $2,507			$ 5	59,151		59,156
Issuance of common stock in initial public offering, net of discounts and commissions of $4,642 and issuance costs of $2,507 (in shares)			5,100,351
Conversion of preferred stock into common stock upon initial public offering	$ (79,022)		$ 15	79,007		79,022
Conversion of preferred stock into common stock upon initial public offering (in shares)	(59,989,268)		14,997,312
Reclassification of preferred stock warrant liability into additional paid-in capital upon initial public offering				261		261
Common stock subject to repurchase				(3)		(3)
Stock-based compensation expense (employee)				1,041		1,041
Stock-based compensation expense (non-employee)				206		206
Equity-based compensation				259		259
Net loss					(25,580)	(25,580)
Comprehensive loss					(25,580)	(25,580)
Balance at Dec. 31, 2013			$ 21	142,071	(85,649)	56,443
Balance (in shares) at Dec. 31, 2013			21,143,313
Increase (Decrease) in Convertible Preferred Stock and Stockholders' Equity (Deficit)
Issuance of common stock on exercise of stock options			$ 1	674		675
Issuance of common stock on exercise of stock options (in shares)			402,100
Reclassification of preferred stock warrant liability into additional paid-in capital upon initial public offering						3
Issuance of common stock on cashless exercise of warrant (in shares)			13,739
Common stock subject to repurchase				3
Issuance of common stock for acquisition			$ 1	10,077		10,078
Issuance of common stock for acquisition (in shares)			964,377
Stock-based compensation expense (employee)				3,388		3,388
Stock-based compensation expense (non-employee)				160		160
Net loss					(29,373)	(29,373)
Comprehensive loss					(29,373)	(29,373)
Balance at Dec. 31, 2014			$ 23	156,373	(115,022)	41,374
Balance (in shares) at Dec. 31, 2014			22,523,529
Increase (Decrease) in Convertible Preferred Stock and Stockholders' Equity (Deficit)
Issuance of common stock on exercise of stock options				722		$ 722
Issuance of common stock on exercise of stock options (in shares)			253,787			253,787
Sale of common stock in a private placement, net of issuance costs			$ 5	37,253		$ 37,258
Sale of common stock in a private placement, net of issuance costs (in shares)			4,907,975
Stock-based compensation expense (employee)				5,302		5,302
Stock-based compensation expense (non-employee)				110		110
Stock-based compensation expense (ESPP)				190		190
Net loss					(33,704)	(33,704)
Comprehensive loss					(33,704)	(33,704)
Balance at Dec. 31, 2015			$ 28	$ 199,950	$ (148,726)	$ 51,252
Balance (in shares) at Dec. 31, 2015			27,685,291

Statements of Convertible Pref6

Statements of Convertible Preferred Stock and Stockholders' Equity (Parenthetical) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2015	Dec. 31, 2013
Issuance of common stock in initial public offering, discounts and commissions			$ 4,642,000
Issuance of common stock in initial public offering, issuance cost			$ 2,507,000
Issuance of common stock in a private placement, issuance cost		$ 2,742,000
Series C
Issuance of convertible preferred stock, issue price (in dollars per share)	$ 1.89
Issuance of convertible preferred stock, issuance cost	$ 53

Statements of Cash Flows

Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating activities
Net loss	$ (33,704)	$ (29,373)	$ (25,580)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,254	1,175	999
Bad debt expense	105	54	109
Genzyme co-promotion fee amortization	(1,897)	(2,269)	(2,500)
Stock-based compensation	5,602	3,548	1,247
Amortization of debt discount and issuance costs	46	97	56
Interest on debt balloon payment	79	81	42
Change in value of preferred stock liability			2,070
Change in value of preferred stock warrant liability			86
Changes in operating assets and liabilities:
Accounts receivable	(558)	(1,961)	(683)
Supplies inventory	(71)	(1,129)	(1,517)
Prepaid expenses and other current assets	304	(38)	(722)
Other assets	(42)	(46)	24
Accounts payable	(3,546)	1,874	3,348
Accrued liabilities and deferred rent	4,463	355	3,862
Net cash used in operating activities	(26,965)	(27,632)	(19,159)
Investing activities
Purchases of property and equipment	(6,165)	(2,024)	(1,332)
Cash remitted for acquisition, net of cash received		(6,916)
Change in restricted cash	(533)	(70)	50
Net cash used in investing activities	(6,698)	(9,010)	(1,282)
Financing activities
Proceeds from the issuance of long-term debt, net of debt issuance costs			4,877
Payment of end-of-term obligation		(110)
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs			12,945
Proceeds from issuance of common stock in a private placement, net of costs	37,258
Proceeds from issuance of common stock in initial public offering, gross			66,304
Commissions and issuance costs relating to the initial public offering		(129)	(7,019)
Payment of deferred stock offering costs	(247)
Proceeds from the exercise of common stock options	722	675	552
Net cash provided by financing activities	37,733	436	77,659
Net increase (decrease) in cash and cash equivalents	4,070	(36,206)	57,218
Cash and cash equivalents at beginning of period	35,014	71,220	14,002
Cash and cash equivalents at end of period	39,084	35,014	71,220
Supplementary cash flow information of non cash investing and financing activities:
Fair value of common stock issued for acquisition		10,078
Non-cash issuance of long-term debt		5,000
Non-cash repayment of long-term debt		(5,000)
Purchases of property and equipment included in accounts payable and accrued liabilities	1,825	383	25
Non-cash purchases of property and equipment			257
Transfer of preferred stock liability to equity			2,653
Preferred stock warrants			175
Conversion of preferred stock warrant liability to common stock warrants			261
Issuance of common stock from the non-cash exercise of common stock warrants		187
Conversion of convertible preferred stock to common stock			79,022
IPO costs included in accounts payable and accrued liabilities			129
Cash paid for interest on debt	278	$ 307	132
Transfer of equity-based compensation from liabilities to equity			$ 259
Cash paid for tax	$ 22

Organization and Description of

Organization and Description of Business	12 Months Ended
	Dec. 31, 2015
Organization and Description of Business
Organization and Description of Business	1. Organization and Description of Business Veracyte, Inc. ("Veracyte" or the "Company") was incorporated in the state of Delaware on August 15, 2006 as Calderome, Inc. Calderome operated as an incubator until early 2008. On March 4, 2008, the Company changed its name to Veracyte, Inc. Veracyte is a molecular diagnostics company that uses genomic technology to resolve diagnostic ambiguity. The Company targets diseases in which large numbers of patients undergo invasive and costly diagnostic procedures that could have been avoided with a more accurate diagnosis from a cytology sample taken preoperatively. By improving preoperative diagnosis, the Company helps patients avoid such unnecessary invasive procedures and surgeries while reducing healthcare costs. The Company's first commercial solution, the Afirma® Thyroid FNA Analysis, centers on the proprietary Afirma Gene Expression Classifier ("GEC"). The Afirma GEC helps physicians reduce the number of unnecessary surgeries by employing a proprietary 142-gene signature to preoperatively determine whether thyroid nodules previously classified by cytopathology as indeterminate can be reclassified as benign. The Afirma GEC is offered directly or as part of a comprehensive solution that also includes cytopathology testing and the Afirma Malignancy Classifiers, launched in May 2014. The Company currently markets and sells Afrma in the United States and select foreign countries through a co-promotion agreement with Genzyme Corporation, a subsidiary of Sanofi, as well as selectively through other distributors internationally. On March 9, 2016, the Company gave notice of termination of the Amended Agreement effective September 9, 2016. In September 2014, the Company acquired Allegro Diagnostics Corp. ("Allegro") to accelerate its entry into pulmonology, the Company's second clinical area. Allegro was a privately-held company based in Maynard, Massachusetts, focused on the development of genomic tests to improve the preoperative diagnosis of lung cancer. See Note 4. In April 2015, the Company entered the lung cancer diagnostics market with the Percepta® Bronchial Genomic Classifier, a new genomic test to resolve ambiguity in lung cancer diagnosis. The Company has a second product in pulmonology under development designed to preoperatively identify patients with idiopathic pulmonary fibrosis ("IPF"). The Company's operations are based in South San Francisco, California and Austin, Texas, and it operates in one segment in the United States. Initial Public Offering On November 4, 2013, the Company completed an initial public offering ("IPO") of its common stock. In connection with its IPO, the Company issued and sold 5,100,351 shares of common stock at a price to the public of $13.00 per share. As a result of the IPO, the Company received $59.2 million in net proceeds, after deducting underwriting discounts and commissions of $4.6 million and offering expenses of $2.5 million payable by the Company. In connection with the IPO, the Company's outstanding shares of convertible preferred stock were automatically converted into 14,997,312 shares of common stock.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2015
Summary of Significant Accounting Policies
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation The Company's financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP"). The financial statements include the accounts of the Company and its former wholly-owned subsidiary, which was dissolved in June 2015. For periods prior to the subsidiary dissolution, all intercompany accounts and transactions were eliminated in consolidation. Use of Estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant items subject to such estimates include: revenue recognition; contractual allowances; allowance for doubtful accounts; the useful lives of property and equipment; the recoverability of long-lived assets; the estimation of the fair value of intangible assets; the determination of fair value of the Company's common stock prior to the Company's IPO; stock options; preferred stock liability; income tax uncertainties, including a valuation allowance for deferred tax assets; and contingencies. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses that are not readily apparent from other sources. Actual results could differ from those estimates and assumptions. Liquidity The Company has incurred net losses since its inception and expects to incur additional losses in 2016 and in future years. As of December 31, 2015, the Company had an accumulated deficit of $148.7 million. The Company may never achieve revenue sufficient to offset its expenses. The Company believes its cash and cash equivalents of $39.1 million as of December 31, 2015 and its revenue from sales in 2016 will be sufficient to meet its anticipated cash requirements for at least the next 12 months. In April 2015, the Company issued and sold 4,907,975 shares of its common stock in a private placement, at a price of $8.15 per share. The Company received $37.3 million in net proceeds, after deducting expenses of $2.7 million. If the Company is not able to generate revenue to finance its cash requirements, the Company will need to finance future cash needs primarily through public or private equity offerings, debt financings, borrowings or strategic collaborations or licensing arrangements. If the Company is not able to secure additional funding when needed, on acceptable terms, it may have to delay, reduce the scope of or eliminate one or more research and development programs or selling and marketing initiatives which may have a material adverse effect on the Company's business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all. Concentrations of Credit Risk and Other Risks and Uncertainties The Company's cash and cash equivalents are deposited with one major financial institution in the United States, as required by the loan and security agreement discussed in Note 8. Deposits in this institution may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents. Several of the components of the Company's sample collection kit and test reagents are obtained from single-source suppliers. If these single-source suppliers fail to satisfy the Company's requirements on a timely basis, it could suffer delays in being able to deliver its diagnostic solutions, a possible loss of revenue, or incur higher costs, any of which could adversely affect its operating results. The Company is also subject to credit risk from its accounts receivable related to its sales. The Company generally does not perform evaluations of customers' financial condition and generally does not require collateral. Through December 31, 2015, all of the Company's revenue have been derived from the sale of Afirma. To date, Afirma has been delivered primarily to physicians in the United States. The Company's third-party payers in excess of 10% of revenue and their related revenue as a percentage of total revenue were as follows: Year Ended December 31, 2015 2014 2013 Medicare % % % United Healthcare % % % Aetna % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As the number of payers reimbursing for Afirma increases, the percentage of revenue derived from Medicare and other significant third-party payers has changed and will continue to change as a percentage of total revenue. The Company's significant third-party payers and their related accounts receivable balance at December 31, 2015 and 2014 as a percentage of total accounts receivable are as follows: December 31, 2015 2014 Medicare % % United Healthcare % % Aetna % % No other third-party payer represented more than 10% of the Company's accounts receivable balances as of those dates. Cash Equivalents Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents consist of amounts invested in a money market account primarily consisting of U.S. Treasury reserves. Restricted Cash The Company had deposits of $118,000 as of December 31, 2015 and December 31, 2014, restricted from withdrawal and held by a bank in the form of collateral for irrevocable standby letters of credit totaling $118,000 held as security for the lease of the Company's headquarters and laboratory facilities in South San Francisco that expires March 31, 2016. This restricted cash is included in current assets as of December 31, 2015 and in long-term assets as of December 31, 2014. The Company also had deposits of $603,000 included in long-term assets as of December 31, 2015, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the Company's new South San Francisco facility signed in April 2015. The Company reserved $70,000 in cash as of December 31, 2014 to cover liabilities associated with the acquisition of Allegro as discussed in Note 4. This amount was paid in March 2015. Allowance for Doubtful Accounts The Company estimates an allowance for doubtful accounts against its individual accounts receivable based on estimates of expected reimbursement consistent with historical payment experience in relation to the amounts billed. Bad debt expense is included in general and administrative expense on the Company's statements of operations and comprehensive loss. Accounts receivable are written off against the allowance when there is substantive evidence that the account will not be paid. The balance of allowance for doubtful accounts as of December 31, 2015 and 2014, including charges to bad debt expense and write-offs, net of recoveries, was as follows (in thousands of dollars): As of December 31, 2015 2014 Beginning balance $ $ Charged to expense Write-offs, net of recoveries ) ) ​ ​ ​ ​ ​ ​ ​ ​ Ending balance $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Supplies Inventory Supplies inventory consists of test reagents and other consumables primarily used in the sample collection kits and in cytopathology and GEC test processing and are valued at the lower of cost or market value. Cost is determined using actual costs on a first-in, first-out basis. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally between three and five years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the term of the lease. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in the statements of operations and comprehensive loss in the period realized. Internal-use Software The Company capitalizes costs incurred in the application development stage to design and implement the software used in the tracking and reporting of laboratory activity. Costs incurred in the development of application software are capitalized and amortized over an estimated useful life of three years on a straight-line basis. The total cost, accumulated depreciation and net book value of internal-use software was $1.3 million, $534,000 and $744,000, respectively, as of December 31, 2015, and was $927,000, $330,000 and $597,000, respectively, as of December 31, 2014, and are included in property and equipment in the Company's balance sheets. During the years ended December 31, 2015 and 2014, the Company capitalized $352,000 and $445,000, respectively, of software development costs. Amortization expense totaled $204,000, $135,000 and $108,000 in the years ended December 31, 2015, 2014 and 2013, respectively. Business Combination The Company accounts for acquisitions using the acquisition method of accounting which requires the recognition of tangible and identifiable intangible assets acquired and liabilities assumed at their estimated fair values as of the business combination date. The Company allocates any excess purchase price over the estimated fair value assigned to the net tangible and identifiable intangible assets acquired and liabilities assumed to goodwill. Transaction costs are expensed as incurred in general and administrative expenses. Results of operations and cash flows of acquired companies are included in the Company's operating results from the date of acquisition. Finite-lived Intangible Assets Finite-lived intangible assets relates to intangible assets reclassified from indefinite-lived intangible assets, following the launch of Percepta in April 2015. The Company amortizes finite-lived intangible assets using the straight-line method over their estimated useful life. The estimated useful life of 15 years was used for the intangible asset related to the Percepta test based on management's estimate of product life, product life of other diagnostic tests and patent life. The Company tests this finite-lived intangible asset for impairment when events or circumstances indicate a reduction in the fair value below its carrying amount. There was no impairment for the year ended December 31, 2015. Indefinite-lived Intangible Assets—In-process Research and Development The Company's indefinite-lived intangible assets are comprised of acquired in-process research and development ("IPR&D"). The fair value of IPR&D acquired through a business combination is capitalized as an indefinite-lived intangible asset until the completion or abandonment of the related research and development activities. When research and development is complete, the associated assets are amortized on a straight-line basis over their estimated useful lives. IPR&D is tested for impairment annually or more frequently if events or circumstances indicate that the fair value may be below the carrying value of the asset. The Company recognizes an impairment loss when the total of estimated future undiscounted cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. There were no impairments for the years ended December 31, 2015 and 2014. Goodwill Goodwill, derived from the Company's acquisition of Allegro, is reviewed for impairment on an annual basis or more frequently if events or circumstances indicate that it may be impaired. The Company's goodwill evaluation is based on both qualitative and quantitative assessments regarding the fair value of goodwill relative to its carrying value. The Company has determined that it operates in a single segment and has a single reporting unit associated with the development and commercialization of diagnostic products. In the event the Company determines that it is more likely than not the carrying value of the reporting unit is higher than its fair value, quantitative testing is performed comparing recorded values to estimated fair values. If impairment is present, the impairment loss is measured as the excess of the recorded goodwill over its implied fair value. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. There were no impairments for the years ended December 31, 2015 and 2014. Derivative Liability The Company accounts for derivative financial instruments as either equity or liabilities based upon the characteristics and provisions of each instrument. The Company recorded the preferred stock liability incurred in connection with its Series C convertible preferred stock and the preferred stock warrant liability related to the issuance of a warrant for Series C convertible preferred stock, each as a derivative financial instrument liability at their fair value on the date of issuance, and the Company re-measured them on each subsequent balance sheet date. The changes in fair value were recognized as a gain or loss from the adjustment to other income (expense), net, in the statements of operations and comprehensive loss. The Company estimated the fair value of this liability using option-pricing models that include assumptions for future financings, expected volatility, expected life, yield and risk-free interest rate. The preferred stock liability was extinguished in June 2013. The warrant to purchase Series C convertible preferred stock was converted into a warrant to purchase the Company's common stock as of the closing of its IPO and was exercised through a cashless exercise in March 2014. Bonus Accruals The Company accrues for liabilities under discretionary employee and executive bonus plans. These estimated compensation liabilities are based on progress against corporate objectives approved by the Board of Directors, compensation levels of eligible individuals, and target bonus percentage levels. The Board of Directors and the Compensation Committee of the Board of Directors review and evaluate the performance against these objectives and ultimately determine what discretionary payments are made. The Company accrued $2.1 million and $1.1 million as of December 31, 2015 and 2014, respectively, for liabilities associated with these employee and executive bonus plans which are included in accrued liabilities in the Company's balance sheets. Fair Value of Financial Instruments The carrying amounts of certain financial instruments including cash and cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Revenue Recognition The Company recognizes revenue in accordance with the provision of ASC 954-605, Health Care Entities—Revenue Recognition. The Company's revenue is generated from the provision of diagnostic services using the Afirma solution and the service is completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the service. The Company recognizes revenue related to billings for Medicare and commercial payers on an accrual basis, net of contractual and other adjustments, when amounts that will ultimately be realized can be estimated. Contractual and other adjustments represent the difference between the list price (the billing rate) and the estimated reimbursement rate for each payer. Upon ultimate collection, the amount received from Medicare and commercial payers where reimbursement was estimated is compared to previous estimates and, if necessary, the contractual allowance is adjusted accordingly. Until a contract has been negotiated with a commercial payer or governmental program, the Afirma solution may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the tests in the event that their insurance declines to reimburse the Company. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is only recognized upon the earlier of payment notification, if applicable, or cash receipt. The estimates of amounts that will ultimately be realized requires significant judgment by management. Some patients have out-of-pocket costs for amounts not covered by their insurance carrier, and the Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. Some payers may not cover the Company's GEC as ordered by the prescribing physician under their reimbursement policies. The Company pursues reimbursement from such patients on a case-by-case basis. In the absence of contracted reimbursement coverage or the ability to estimate the amount that will ultimately be realized for the Company's services, revenue is recognized upon the earlier of receipt of third-party payer notification of payment or when cash is received. Revenue recognized when cash is received and on an accrual basis for the years ended December 31, 2015, 2014 and 2013 was as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Revenue recognized when cash is received $ $ $ Revenue recognized on an accrual basis ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Cost of Revenue Cost of revenue is expensed as incurred and includes material and service costs, cytopathology testing services performed by a third-party pathology group, stock-based compensation expense, direct labor costs, equipment and infrastructure expenses associated with testing samples, shipping charges to transport samples, and allocated overhead including rent, information technology, equipment depreciation and utilities. Research and Development Research and development costs are charged to operations as incurred. Research and development costs include payroll and personnel-related expenses, stock-based compensation expense, prototype materials, laboratory supplies, consulting costs, costs associated with setting up and conducting clinical studies at domestic and international sites, and allocated overhead including rent, information technology, equipment depreciation and utilities. Income Taxes The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. The Company's assessment of an uncertain tax position begins with the initial determination of the position's sustainability and is measured at the largest amount of benefit that is more-likely-than-not of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit may change as new information becomes available. Stock-based Compensation Stock-based compensation expense for equity instruments issued to employees is measured based on the grant-date fair value of the awards. The fair value of each employee stock option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recognizes compensation costs on a straight-line basis for all employee stock-based compensation awards that are expected to vest over the requisite service period of the awards, which is generally the awards' vesting period. Forfeitures are required to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Equity awards issued to non-employees are valued using the Black-Scholes option-pricing model and are subject to re-measurement as the underlying equity awards vest. Net Loss per Common Share Basic net loss per common share is calculated by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury stock method. Potentially dilutive securities consisting of options and warrants to purchase common stock are considered to be common stock equivalents and were excluded from the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers , requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The updated standard will replace most existing revenue recognition guidance in GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. Adoption is permitted as early as the first quarter of 2017 and is required by the first quarter of 2018. The Company has not yet selected a transition method and are currently evaluating the potential effect of the updated standard on its financial statements. In August 2014, FASB issued ASU No. 2014-15, Presentation of Financial Statements Going Concern—Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern . The amendments require management to assess an entity's ability to continue as a going concern by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. Specifically, the amendments: (1) provide a definition of the term substantial doubt; (2) require an evaluation every reporting period including interim periods; (3) provide principles for considering the mitigating effect of management's plans; (4) require certain disclosures when substantial doubt is alleviated as a result of consideration of management's plans; (5) require an express statement and other disclosures when substantial doubt is not alleviated; and (6) require an assessment for a period of one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 will be effective for annual periods ending after December 15, 2016 and interim periods within annual periods beginning after December 15, 2016 with early adoption permitted. ASU 2014-15 will be effective for the Company beginning with its annual report for fiscal 2016 and interim periods thereafter. The Company does not anticipate that the adoption of this ASU will have a significant impact on its financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs , to require debt issuance costs to be presented as an offset against debt outstanding. The update does not change current guidance on the recognition and measurement of debt issuance costs. The ASU is effective for interim and annual periods beginning after December 15, 2015. Adoption of the ASU is retrospective to each prior period presented. The Company does not anticipate that the adoption of this ASU will have a significant impact on its balance sheet. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes , related to balance sheet classification of deferred taxes. The ASU requires that deferred tax assets and liabilities be classified as noncurrent in the statement of financial position, thereby simplifying the current guidance that requires an entity to separate deferred assets and liabilities into current and noncurrent amounts. The ASU will be effective for the Company beginning in the first quarter of fiscal year 2018 though early adoption is permitted. The Company has early-adopted the ASU as of December 31, 2015 and its statement of financial position as of this date reflects the revised classification of current deferred tax assets and liabilities as noncurrent. The Company has early-adopted this ASU prospectively and prior periods have not been retrospectively adjusted. There is no other impact on the Company's financial statements of early-adopting the ASU.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2015
Net Loss Per Share
Net Loss Per Share	3. Net Loss Per Share The following table presents the calculation of basic and diluted net loss per common share for the years ended December 31, 2015, 2014 and 2013 (in thousands of dollars, except share and per share amounts): Year Ended December 31, 2015 2014 2013 Net loss $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shares used to compute net loss per common share, basic and diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per common share, basic and diluted $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The following outstanding common stock equivalents have been excluded from diluted net loss per common share for the years ended December 31, 2015, 2014 and 2013 because their inclusion would be anti-dilutive: Year Ended December 31, 2015 2014 2013 Shares of common stock subject to outstanding options Shares of common stock issuable upon exercise of warrants — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total shares of common stock equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Business Combination

Business Combination	12 Months Ended
	Dec. 31, 2015
Business Combination
Business Combination	4. Business Combination In September 2014, the Company acquired Allegro via a merger with Full Moon Acquisition, Inc., a wholly-owned subsidiary of the Company. Allegro was a privately-held company based in Maynard, Massachusetts, focused on the development of genomic tests to improve the preoperative diagnosis of lung cancer. Allegro merged with Full Moon, (the "Merger"), with Allegro surviving the Merger as a wholly-owned subsidiary of the Company. The subsidiary was dissolved in June 2015. At the effective time of the Merger, each share of the common stock of Full Moon issued and outstanding immediately prior to the effective time of the Merger was automatically converted into one share of common stock of Allegro and represented the only outstanding common stock of Allegro at the effective time of the Merger; all previously issued and outstanding shares of common stock of Allegro were canceled. The Series A preferred stock of Allegro issued and outstanding immediately prior to the effective time of the Merger was canceled and automatically converted into the right to receive a total of 964,377 shares of the Company's common stock and $2.7 million in cash. Outstanding indebtedness of Allegro totaling $4.3 million was settled in cash by the Company on the effective date of the Merger. All outstanding stock options under Allegro's equity incentive plan were canceled. The acquisition of Allegro accelerated the Company's entry into the pulmonology diagnostics market. Allegro's lung cancer test is designed to help physicians determine which patients with lung nodules who have had an inconclusive bronchoscopy result are at low risk for cancer and can thus be safely monitored with CT scans rather than undergoing invasive procedures. The Company launched the Percepta test in April 2015. The Merger was accounted for using the acquisition method of accounting with the Company treated as the accounting acquirer. The purchase price was allocated based on the estimated fair value of the assets acquired and liabilities assumed at the date of the acquisition. The Company incurred approximately $0.5 million in acquisition-related costs related to the Merger, which primarily consisted of legal, accounting and valuation-related expenses. In addition, the Company incurred $1.2 million related to transaction bonuses and severance payments to former Allegro employees associated with the Merger. These expenses were recorded in general and administrative expense in the accompanying statements of operations and comprehensive loss. Total expenses and net loss associated with the acquired Allegro business in the Company's statements of operations and comprehensive loss were not separately identifiable due to the integration with the Company's operations. The acquisition consideration was comprised of (in thousands of dollars): Stock $ Cash Payment of outstanding indebtedness ​ ​ ​ ​ ​ Total acquisition consideration $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The stock consideration of $10.1 million was determined based on the closing price of the Company's common stock on September 16, 2014 ($10.45 per share). The fair value of the assets acquired and liabilities assumed at the closing date of the Merger are summarized below (in thousands of dollars): Cash and cash equivalents $ Other assets, net In-process research and development Goodwill ​ ​ ​ ​ ​ Total net assets acquired $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The fair value of IPR&D was determined using the multi-period excess earnings method of the income approach, which estimates the economic benefits of the IPR&D over multiple time periods by identifying the cash flows associated with the use of the asset, based on forecasts prepared by management, and deducting a periodic charge reflecting a fair return for the use of contributory assets. The forecasted cash flows were discounted based on a discount rate of 18.5%. The discount rate represents the Company's weighted average return on assets and was benchmarked against the internal rate of return and cost of capital of guideline publicly traded companies. The fair value of the IPR&D was capitalized as of the closing date of the Merger and was accounted for as an indefinite-lived intangible asset prior to the beginning of amortization. Amortization of the IPR&D began in April 2015 when research and development activities were deemed to be completed and is recorded on a straight-line basis. The amortization period of the IPR&D is over its estimated useful life of 15 years after taking into consideration expected use of the asset, legal or regulatory provisions that may limit or extend the life of the asset, as well as the effects of obsolescence and other economic factors. Amortization of $800,000 was recorded for the year ended December 31, 2015 and accumulated amortization was $800,000 as of December 31, 2015. Amortization expense will be approximately $1.1 million per year. Goodwill, which represents the purchase price in excess of the fair value of net assets acquired, is not expected to be deductible for income tax purposes. This goodwill is reflective of the value derived from the acceleration of the Company's entry into the pulmonology market. Pro Forma Financial Information (Unaudited) The following pro forma financial information is based on the historical financial statements of the Company and presents the Company's results as if the Merger had occurred as of January 1, 2013 (in thousands of dollars): Year Ended December 31, 2014 2013 Revenue $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The pro forma results present the combined historical results of operations with adjustments to reflect one-time charges including: • The reversal of costs related to transaction bonuses and other payments to employees and acquisition-related expenses directly related to the Merger of $2.2 million for the year ended December 31, 2014; and • the elimination of interest expense related to Allegro indebtedness of $2.3 million and $4.5 million for the years ended December 31, 2014 and 2013, respectively. The pro forma information presented does not purport to present what the actual results would have been had the Merger actually occurred on January 1, 2013, nor is the information intended to project results for any future period.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2015
Balance Sheet Components
Balance Sheet Components	5. Balance Sheet Components Property and Equipment, Net Property and equipment consisted of the following (in thousands of dollars): Year Ended December 31, 2015 2014 Leasehold improvements $ $ Laboratory equipment Computer equipment Software, including software developed for internal use Furniture and fixtures Construction-in-process ​ ​ ​ ​ ​ ​ ​ ​ Total property and equipment, at cost Accumulated depreciation and amortization ) ) ​ ​ ​ ​ ​ ​ ​ ​ Total property and equipment, net $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Depreciation and amortization expense was $1.5 million, $1.2 million and $1.0 million for the years ended December 31, 2015, 2014 and 2013, respectively. Accrued Liabilities Accrued liabilities consisted of the following (in thousands of dollars): Year Ended December 31, 2015 2014 Accrued compensation expenses $ $ Accrued Genzyme co-promotion fees Accrued other ​ ​ ​ ​ ​ ​ ​ ​ Total accrued liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2015
Fair Value Measurements
Fair Value Measurements	6. Fair Value Measurements The Company records its financial assets and liabilities at fair value. The carrying amounts of certain financial instruments of the Company, including cash and cash equivalents, prepaid expenses and other current assets, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities. The carrying value of debt approximates its fair value because the interest rate approximates market rates that the Company could obtain for debt with similar terms. The accounting guidance for fair value provides a framework for measuring fair value, clarifies the definition of fair value, and expands disclosures regarding fair value measurements. Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability (an exit price) in an orderly transaction between market participants at the reporting date. The accounting guidance establishes a three-tiered hierarchy, which prioritizes the inputs used in the valuation methodologies in measuring fair value as follows: • Level I: Inputs which include quoted prices in active markets for identical assets and liabilities. • Level II: Inputs other than Level I that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level III: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. The fair value of the Company's financial assets, which consist only of money market funds, was $37.5 million and $33.2 million as of December 31, 2015 and December 31, 2014, respectively, and are Level I assets as described above. The Company has no Level III liabilities as of December 31, 2015 and 2014. The following table sets forth the changes in the fair value of the Company's Level III financial liabilities, which consisted of a preferred stock liability during 2013, which were measured on a recurring basis (in thousands of dollars): Year Ended December 31, 2013 Beginning balance $ Change in fair value of preferred stock liability recorded as other expense, net Settlement of preferred stock liability ) Fair value of preferred stock warrant liability Change in fair value of preferred stock warrant liability recorded as other expense, net Conversion of preferred stock warrant liability ) ​ ​ ​ ​ ​ Ending balance $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ In November 2012, the Company recorded a preferred stock liability as investors received the right to purchase from the Company, on the same terms, additional shares of Series C convertible preferred stock, in a second tranche. As the investors held a majority of the board seats, the decision to complete the second tranche was deemed to be outside the control of the Company. The preferred stock liability was valued using the option-pricing method, which resulted in an initial fair value of $0.9 million for the Company's obligation to sell the convertible preferred stock. In June 2013, the Company settled the preferred stock liability upon completion of the sale of the second tranche of Series C convertible preferred stock. Immediately prior to settlement, the Company revalued the preferred stock liability to $2.7 million and recorded other expense of $2.1 million related to the change in value of the liability through that date. The preferred stock liability was valued using the option-pricing method with the following assumptions: 100% probability of success of the second tranche, fair value of Series C preferred stock of $2.39, a term of 0.003 years and expected volatility of 36.4%.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies
Commitments and Contingencies	7. Commitments and Contingencies Operating Leases The Company leases its headquarters and South San Francisco, California laboratory facilities under a non-cancelable lease agreement that expires on March 31, 2016. In April 2015, the Company signed a non-cancelable lease agreement for approximately 59,000 square feet to serve as its new South San Francisco facility. The lease began in June 2015 and ends in March 2026 and contains extension of lease term and expansion options. In conjunction with this lease, the landlord provided funding of approximately $3.3 million for tenant improvements, all of which has been received as of December 31, 2015. The Company has incurred approximately $2.7 million in addition to the landlord's tenant allowance as of December 31, 2015 and expects to incur further costs of $1.3 million in 2016 to complete the build-out of the facility. The Company had deposits of $603,000 included in long-term assets as of December 31, 2015, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit totaling $603,000 held as security for the lease of the new South San Francisco facility. The Company also leases laboratory space in Austin, Texas. The lease expires on July 31, 2018. The Company provided a cash security deposit of $75,000, which is included in other assets in the Company's balance sheets as of December 31, 2015 and 2014. Future minimum lease payments under non-cancelable operating leases as of December 31, 2015 are as follows (in thousands of dollars): Year Ending December 31, Amounts 2016 $ 2017 2018 2019 2020 Thereafter ​ ​ ​ ​ ​ Total minimum lease payments $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The Company recognizes rent expense on a straight-line basis over the non-cancelable lease period. Facilities rent expense was $1.9 million, $852,000 and $840,000 for the years ended December 31, 2015, 2014 and 2013, respectively. Until the new South San Francisco facility is utilized, rent of approximately $500,000 per quarter will be charged to general and administrative expense. Supplies Purchase Commitments The Company had non-cancelable purchase commitments with two suppliers to purchase a minimum quantity of supplies for approximately $837,000 at December 31, 2015. Debt Obligations See Note 8, Debt. Contingencies From time to time, the Company may be involved in legal proceedings arising in the ordinary course of business. The Company believes there is no litigation pending that could have, individually or in the aggregate, a material adverse effect on the financial position, results of operations or cash flows.

Debt

Debt	12 Months Ended
	Dec. 31, 2015
Debt
Debt	8. Debt In June 2013, the Company entered into a loan and security agreement ("Original Loan") with a financial institution. The Original Loan provided for term loans of up to $10.0 million in aggregate. The Company drew down $5.0 million in funds under the agreement in June 2013, and did not draw the remaining $5.0 million on or before the expiration date of March 31, 2014. The Company was required to repay the outstanding principal in 30 equal installments beginning 18 months after the date of the borrowing and was due in full in June 2017. The Original Loan had an interest rate of 6.06% per annum, carried prepayment penalties of 2.25% and 1.50% for prepayment within one and two years, respectively, and 0.75% thereafter. In December 2014, the Company amended certain terms and conditions of the Original Loan ("Amended Loan"). The Amended Loan provides for term loans of up to $15.0 million in aggregate, in three tranches of $5.0 million each. The Company borrowed $5.0 million under the first tranche in December 2014 and used the funds for repayment of the $5.0 million in principal outstanding under the Original Loan, in a cashless transaction. In addition, the Company paid the accrued but unpaid interest of $14,000 due on the Original Loan and the related end-of-term payment of $110,000. The Amended Loan waived the prepayment premium of $75,000 under the Original Loan and reduced the end-of-term payment of $225,000 under the Original Loan to $110,000. In November 2015, the Company further amended the loan to extend the availability of the second $5.0 million tranche under the Amended Loan through June 30, 2016 from December 31, 2015 originally. The Company may borrow the third $5.0 million tranche any time through June 30, 2016 after achieving the third tranche revenue milestone as defined in the Amended Loan. The carrying value of the debt approximates its fair value because the interest rate approximates market rates that the Company could obtain for debt with similar terms. Under the Amended Loan borrowing, the Company is required to repay the outstanding principal in 24 equal installments beginning 24 months after the date of the borrowing and is due in full in December 2018. The first tranche of the Amended Loan bears interest at a rate of 5.00% per annum. The Amended Loan carries prepayment penalties of 2.00% and 1.00% for prepayment within one and two years, respectively, and no prepayment penalty thereafter. In connection with the Amended Loan, the Company paid approximately $45,000 in third-party fees. The Amended Loan resulted in a debt modification under ASC 470-50, Modifications and Extinguishments, as the change in present value of the remaining cash flows associated with the Original Loan and Amended Loan are not substantial. As of December 31, 2015 and 2014, the net debt obligation was as follows (in thousands of dollars): December 31, 2015 2014 Debt and unpaid accrued end-of-term payment $ $ Unamortized note discount ) ) ​ ​ ​ ​ ​ ​ ​ ​ Net debt obligation $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Future principal payments under the Amended Loan are as follows (in thousands of dollars): Year ending December 31: 2016 $ — 2017 2018 ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The obligation at December 31, 2015 includes $82,000 of an end-of-term payment of $237,500, representing 4.75% of the total outstanding principal balance, which accretes over the life of the loan as interest expense. As a result of the debt discount and the end-of-term payment, the effective interest rate for the loan differs from the contractual rate. Interest expense on the debt was as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Nominal interest $ $ $ Amortization of debt discount and debt issuance costs End-of-term payment interest ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Upon execution of the Original Loan, the Company issued the financial institution a warrant to purchase shares of Series C convertible preferred stock at $7.56 per share. At the time of issuance, the aggregate fair value of the warrant for the 24,801 shares exercisable under the warrant was $175,000. The fair value of the warrant was deducted from total proceeds, resulting in a debt discount to be amortized to interest expense over 48 months, through the maturity date of the Original Loan, using the effective interest rate method, and was recorded as a preferred stock warrant liability. The warrant was converted to a warrant to purchase the Company's common stock upon the completion of the Company's IPO. See Note 9. The Company's obligations under the Amended Loan are secured by a security interest in substantially all of its assets, excluding its intellectual property and certain other assets. The Amended Loan contains customary conditions related to borrowing, events of default, and covenants, including covenants limiting the Company's ability to dispose of assets, undergo a change in control, merge with or acquire other entities, incur debt, incur liens, pay dividends or other distributions to holders of its capital stock, repurchase stock and make investments, in each case subject to certain exceptions. The Amended Loan also allows the lender to call the debt in the event there is a material adverse change in the Company's business or financial condition. The Company is required to be in compliance with a minimum liquidity or minimum revenue covenant. As of December 31, 2015, the Company was in compliance with the financial covenants.

Convertible Preferred Stock War

Convertible Preferred Stock Warrant	12 Months Ended
	Dec. 31, 2015
Convertible Preferred Stock Warrant
Convertible Preferred Stock Warrant	9. Convertible Preferred Stock Warrant In June 2013, in conjunction with the execution of the Original Loan, as discussed in Note 8, the Company issued to the lender a warrant to purchase up to 49,602 shares of Series C convertible preferred stock with an exercise price of $7.56 per share. Upon the draw-down of the $5.0 million term loan, the related warrant became exercisable for 24,801 shares. In November 2013, in connection with the Company's IPO, the warrant automatically became exercisable for 24,801 shares at an exercise price of $7.56 per share. The lender exercised the warrant with respect to 24,801 shares through a cashless exercise in March 2014, resulting in the issuance of 13,739 shares of the Company's common stock. The fair value of the then currently exercisable portion of the warrant in the amount of $175,000 was recorded as a preferred stock warrant liability upon issuance and was subject to re-measurement at each reporting period up to the closing date of the IPO when the Series C preferred stock converted into common stock. The fair value of the warrant upon issuance was calculated using the Black-Scholes option-pricing model with the following assumptions: Series C preferred stock value of $2.40 per share, contractual term of 7.3 years, risk-free interest rate of 2.1%, expected volatility of 73.7%, and expected dividend yield of 0%. Just prior to the closing of the IPO, the fair value of the warrant was approximately $261,000, and was calculated using the Black-Scholes option-pricing model with the following assumptions: Series C preferred stock value of $13.14 per share, contractual term of 7.0 years, risk-free interest rate of 2.0%, expected volatility of 81.4%, and expected dividend yield of 0%. The change in the fair value of approximately $86,000 was reported as an expense for the year ended December 31, 2013 and was included in other income (expense), net, in the statements of operations and comprehensive loss. The warrant was converted into a warrant to purchase common stock upon the completion of the IPO in 2013, and was reclassified to additional paid-in-capital on the Company's balance sheet.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2015
Convertible Preferred Stock
Convertible Preferred Stock	10. Convertible Preferred Stock In November 2012, the Company recorded a preferred stock liability as the investors received the right to purchase from the Company, on the same terms, additional shares of Series C convertible preferred stock, in a second tranche. As the investors held a majority of the board seats, the decision to complete the second tranche was deemed to be outside the control of the Company. The preferred stock liability was valued using the option-pricing method with the following assumptions: 100% probability of success of the second tranche, fair value of Series C preferred stock of $1.78, a term of 0.67 years and expected volatility of 44%. This resulted in an initial fair value of $0.9 million for the Company's obligation to sell the convertible preferred stock. At December 31, 2012, the Company revalued the preferred stock liability to $0.6 million, and recorded the $0.3 million valuation decrease to other income (expense), net, in the Company's statements of operations and comprehensive loss. In June 2013, the Company revalued the preferred stock liability to $2.7 million and recorded the $2.1 million valuation increase to other income (expense), net, in the Company's statements of operations and comprehensive loss. In June 2013, the $2.7 million liability was settled upon the issuance of the second tranche of Series C convertible preferred stock and was reclassified to additional paid-in-capital in the Company's balance sheets. On November 4, 2013, the Company completed its IPO. In connection with the IPO, 59,989,268 outstanding shares of convertible preferred stock were automatically converted into 14,997,312 shares of common stock.

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit)	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity (Deficit)
Stockholders' Equity (Deficit)	11. Stockholders' Equity Common Stock The Company's Restated Certificate of Incorporation authorizes the Company to issue 125,000,000 shares of common stock with a par value of $0.001 per share. The holder of each share of common stock shall have one vote for each share of stock. The common stockholders are also entitled to receive dividends whenever funds and assets are legally available and when declared by the Board of Directors, subject to the prior rights of holders of all series of convertible preferred stock outstanding. No dividends have been declared as of December 31, 2015. As of December 31, 2015 and 2014, the Company had reserved shares of common stock for issuance as follows: December 31, 2015 2014 Options issued and outstanding Options available for grant under stock option plans Common Stock available for the Employee Stock Purchase Plan — ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ In April 2015, the Company completed a private placement of 4,907,975 shares of its common stock to certain accredited investors (the "Investors") at a purchase price of $8.15 per share. Gross proceeds to the Company were $40.0 million and the Company received $37.3 million in net proceeds, after deducting placement agent fees and other expenses payable by the Company of $2.7 million. Employee Stock Purchase Plan In May 2015, the Company's stockholders approved the Company's Employee Stock Purchase Plan ("ESPP"). The ESPP provides eligible employees with an opportunity to purchase common stock from the Company and to pay for their purchases through payroll deductions. The ESPP will be implemented through a series of offerings of purchase rights to eligible employees. Under the ESPP, the Compensation Committee of the Company's Board of Directors may specify offerings with a duration of not more than 12 months, and may specify shorter purchase periods within each offering. During each purchase period, payroll deductions will accumulate, without interest. On the last day of the purchase period, accumulated payroll deductions will be used to purchase common stock for employees participating in the offering. The purchase price will be specified pursuant to the offering, but cannot, under the terms of the ESPP, be less than 85% of the fair market value per share of the Company's common stock on either the offering date or on the purchase date, whichever is less. The Company's Board of Directors has determined that the purchase periods initially shall have a duration of six months, that the first purchase period began on August 3, 2015 and that the purchase price will be 85% of the fair market value per share of the Company's common stock on either the offering date or the purchase date, whichever is less. The length of the purchase period applicable to U.S. employees and the purchase price may not be changed without the approval of the independent members of the Compensation Committee of the Company's Board of Directors. The Compensation Committee has determined that if the fair market value of a share of the Company's common stock on any purchase date within a particular offering period is less than the fair market value on the start date of that offering period, then the offering period will automatically terminate and the employees in that offering period will automatically be transferred and enrolled in a new offering period which will begin on the next day following such purchase date. No employee may purchase more than 2,500 shares, or such lesser number of shares as may be determined by the Compensation Committee with respect to a single offering period, or purchase period, if applicable. In addition, no employee is permitted to accrue, under the ESPP, a right to purchase stock of the Company having a value in excess of $25,000 of the fair market value of such stock (determined at the time the right is granted) for each calendar year. Stock compensation expense of $190,000 was recorded associated with the ESPP for the year ended December 31, 2015. The estimated grant date fair value of the ESPP shares was calculated using the Black-Scholes option-pricing model, based on the following assumptions: December 31, 2015 Weighted-average volatility 53.57 - 58.10% Weighted-average expected term (years) 0.49 - 0.99 Risk-free interest rate 0.17 - 0.33% Expected dividend yield —

Stock Incentive Plans

Stock Incentive Plans	12 Months Ended
	Dec. 31, 2015
Stock Incentive Plans
Stock Incentive Plans	12. Stock Incentive Plans Stock Option Plans In February 2008, the Company adopted the 2008 Stock Plan (the "2008 Plan"). The 2008 Plan provides for the granting of options to purchase common stock and common stock to employees, directors and consultants of the Company. The Company may grant incentive stock options ("ISOs"), non-statutory stock options ("NSOs") or restricted stock under the 2008 Plan. ISOs may only be granted to Company employees (including directors who are also considered employees). NSOs and restricted stock may be granted to Company employees, directors and consultants. Options may be granted for terms of up to ten years from the date of grant, as determined by the Board of Directors, provided however, that with respect to an ISO granted to a person who owns stock representing more than 10% of the voting power of all classes of stock of the Company, the term shall be for no more than five years from the date of grant. The exercise price of options granted must be at a price no less than 100% of the estimated fair value of the shares on the date of grant, as determined by the Board of Directors, provided however, that with respect to an ISO granted to an employee who at the time of grant of such option owns stock representing more than 10% of the voting power of all classes of stock of the Company, the exercise price shall not be less than 110% of the estimated fair value of the shares on the date of grant. Options granted to newly hired employees generally vest over four years (generally 25% after one year and monthly thereafter). Options granted to employees as part of their annual bonus compensation are generally fully vested at the grant date. In October 2013, the Company adopted the 2013 Stock Incentive Plan (the "2013 Plan"). The 2013 Plan was subsequently approved by the Company's stockholders and became effective on November 4, 2013, immediately before the closing of the Company's IPO. Following the effectiveness of the 2013 Plan, no additional options will be granted under the 2008 Plan. An aggregate of 1,700,000 shares were initially reserved for issuance under the 2013 Plan. In addition, to the extent that any awards outstanding or subject to vesting restrictions under the 2008 Plan are subsequently forfeited or terminated for any reason before being exercised or settled, the shares of common stock reserved for issuance pursuant to such awards as of the closing of the IPO will become available for issuance under the 2013 Plan. The remaining shares available for grant under the 2008 Plan became available for issuance under the 2013 Plan upon the closing of the IPO. On the first day of each year from 2014 to 2023, the 2013 Plan authorizes an annual increase of the lesser of 4% of outstanding shares on the last day of the immediately preceding fiscal year or a lesser amount as determined by the Company's Board of Directors. As of December 31, 2015, 1,058,359 shares were available for future issuance under the 2013 Plan. Pursuant to the 2013 Plan, stock options, restricted shares, stock units, including restricted stock units and stock appreciation rights may be granted to employees, consultants, and outside directors of the Company. Options granted may be either ISOs or NSOs. Stock options are governed by stock option agreements between the Company and recipients of stock options. ISOs and NSOs may be granted under the 2013 Plan at an exercise price of not less than 100% of the fair market value of the common stock on the date of grant, determined by the Compensation Committee of the Board of Directors. Options become exercisable and expire as determined by the Compensation Committee, provided that the term of ISOs may not exceed ten years from the date of grant. Stock option agreements may provide for accelerated exercisability in the event of an optionee's death, disability, or retirement or other events. Any outside director who was not previously an employee and who first joins the Company's Board of Directors on or after the effective date of the 2013 Plan will be automatically granted an initial NSO to purchase 35,000 shares of common stock upon first becoming a member of the Board of Directors. Twenty-five percent of the shares subject to the initial option will vest and become exercisable on the first anniversary of the date of grant. The balance ( i.e., the remaining 75%) will vest and become exercisable over three years in equal monthly installments. On the first business day after each regularly scheduled annual meeting of stockholders, each outside director who was not elected to the Board of Directors for the first time at such meeting and who will continue serving as a member of the Board of Directors thereafter will be automatically granted an option to purchase 10,000 shares of common stock, provided that the outside director has served on the Board of Directors for at least six months. Each annual option will vest and become exercisable on the first anniversary of the date of grant, or immediately prior to the next regular annual meeting of the Company's stockholders following the date of grant if the meeting occurs prior to the first anniversary date. The options granted to outside directors will have a per share exercise price equal to 100% of the fair market value of the underlying shares on the date of grant and will become fully vested in the event of a change of control. In addition, such options will terminate on the earlier of (i) the day before the 10th anniversary of the date of grant or (ii) the date 12 months after the termination of the outside director's service for any reason. The following table summarizes activity under the Company's stock option plans (aggregate intrinsic value in thousands): Shares Available for Grant Stock Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value Balance—December 31, 2014 $ $ Additional options authorized — Granted ) Canceled ) Exercised — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance—December 31, 2015 $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options vested and exercisable—December 31, 2015 $ $ Options vested and expected to vest—December 31, 2015 $ $ The aggregate intrinsic value was calculated as the difference between the exercise price of the options to purchase common stock and the fair market value of the Company's common stock, which was $7.20 and $9.66 per share as of December 31, 2015 and 2014, respectively. The weighted average fair value of options to purchase common stock granted was $5.12, $9.08 and $4.19 for the years ended December 31, 2015, 2014 and 2013, respectively. The weighted average fair value of stock options vested was $7.01, $3.07 and $2.12 per share for the years ended December 31, 2015, 2014 and 2013, respectively. The aggregate estimated grant date fair value of employee options to purchase common stock vested during the years ended December 31, 2015 and 2014 was $5.3 million and $1.6 million, respectively. The weighted-average fair value of stock options exercised was $2.00 and $1.18 for the years ended December 31, 2015 and 2014, respectively. The intrinsic value of stock options exercised was $1.8 million, $3.2 million and $4.9 million for the years ended December 31, 2015, 2014 and 2013, respectively. Stock-based Compensation The following table summarizes stock-based compensation expense related to stock options for the years ended December 31, 2015, 2014 and 2013, and are included in the statements of operations and comprehensive loss as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Cost of revenue $ $ $ Research and development Selling and marketing General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total stock-based compensation expense $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As of December 31, 2015, the Company had $10.6 million of unrecognized compensation expense related to unvested stock options, which is expected to be recognized over an estimated weighted-average period of 2.70 years. The estimated grant-date fair value of employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions: Year Ended December 31, 2015 2014 2013 Weighted-average volatility 52.56 - 68.82% 70.19 - 78.54% 80.42 - 81.41% Weighted-average expected term (years) 5.50 - 6.08 5.50 - 6.08 5.00 - 6.08 Risk-free interest rate 1.55 - 2.03% 1.66 - 2.04% 0.88 - 2.11% Expected dividend yield — — — The estimated fair value of non-employee stock options was calculated using the Black-Scholes option-pricing model, based on the following assumptions: Year Ended December 31, 2015 2014 2013 Weighted-average volatility 64.72 - 74.48% 73.20 - 74.48% 77.86 - 78.14% Weighted-average expected term (years) 7.92 - 10.00 8.75 - 10.00 7.72 - 9.75 Risk-free interest rate 1.78 - 2.29% 2.09 - 2.20% 2.59 - 2.99% Expected dividend yield — — — Equity-based Compensation In February 2013, the Company's Board of Directors authorized the grant of 100,498 fully vested stock options at a fair value of $2.59 per option, determined using the Black-Scholes option-pricing valuation model, resulting in a $259,000 expense in the year ended December 31, 2012. Upon issuance of the options, the accrued liability was reclassified into additional paid-in capital. For the years ended December 31, 2015, 2014 and 2013, the Company paid executive bonuses only in the form of cash.

Genzyme Co-promotion Agreement

Genzyme Co-promotion Agreement	12 Months Ended
	Dec. 31, 2015
Genzyme Co-promotion Agreement
Genzyme Co-promotion Agreement	13. Genzyme Co-Promotion Agreement In January 2012, the Company and Genzyme Corporation ("Genzyme") executed a co-promotion agreement for the co-exclusive rights and license to promote and market the Company's Afirma thyroid diagnostic solution in the United States and in 40 named countries. In exchange, the Company received a $10.0 million upfront co-promotion fee from Genzyme in February 2012. Under the terms of the agreement, Genzyme will receive a percentage of U.S. cash receipts that the Company has received related to Afirma as co-promotion fees. The percentage was 50% in 2012, 40% from January 2013 through February 2014, and 32% beginning in February 2014. Genzyme's obligation to also spend up to $500,000 for qualifying clinical development activities in countries that require additional testing for approval expired in July 2014. In November 2014, the Company signed an Amended and Restated U.S. Co-Promotion Agreement ("Amended Agreement") with Genzyme. Under the Amended Agreement, the co-promotion fees Genzyme will receive as a percentage of U.S. cash receipts were reduced from 32% to 15% beginning January 1, 2015. Through August 11, 2014, the Company amortized the $10.0 million upfront co-promotion fee straight-line over a four-year period, which was management's best estimate of the life of the agreement, in part because after that period either party could have terminated the agreement without penalty. Effective August 12, 2014, the Company extended the amortization period from January 2016 to June 2016, the modified earliest period either party could terminate the agreement without penalty. The Company accounted for the change in accounting estimate prospectively. The extension of the amortization period to June 2016 decreased the loss from operations and net loss by $0.6 million and $0.2 million for the years ended December 31, 2015 and 2014, respectively. This extension of amortization to June 2016 also decreased the loss per common share by $0.02 and $0.01 for the years ended December 31, 2015 and 2014, respectively. Either party may terminate the agreement with six months prior notice, however, under the Amended Agreement, neither party can terminate the agreement for convenience prior to June 30, 2016. The agreement with Genzyme expires in 2027. See Note 17, Subsequent Event. In February 2015, the Company entered into an Ex-U.S. Co-promotion Agreement with Genzyme for the promotion of the Afirma GEC test with exclusivity in five countries outside the United States initially and in other countries agreed to from time to time. The agreement commenced on January 1, 2015 and continues until December 31, 2019, with extension of the agreement possible upon agreement of the parties. Country-specific terms have been established under this agreement for Brazil and Singapore and a right of first negotiation has been established for Canada, the Netherlands and Italy. The Company will pay Genzyme 25% of net revenue from the sale of the Afirma GEC test in Brazil and Singapore over a five-year period commencing January 1, 2015. Beginning in the fourth year of the agreement, if the Company terminates the agreement for convenience, the Company may be required to pay a termination fee contingent on the number of GEC billable results generated. The Company incurred $7.3 million, $12.0 million and $8.6 million in co-promotion expense, excluding the amortization of the up-front co-promotion fee, in the years ended December 31, 2015, 2014 and 2013, respectively, and is included in selling and marketing expenses in the statements of operations and comprehensive loss. The Company's outstanding obligation to Genzyme totaled $2.1 million and $6.0 million at December 31, 2015 and December 31, 2014, respectively. The $2.1 million obligation at December 31, 2015 is included in accrued liabilities on the Company's balance sheets. Of the $6.0 million obligation at December 31, 2014, $2.7 million is included in accounts payable and $3.3 million is included in accrued liabilities on the Company's balance sheets. The Company amortized $1.9 million, $2.3 million and $2.5 million of the $10.0 million up-front co-promotion fee in the years ended December 31, 2015, 2014 and 2013, respectively, which is reflected as a reduction to selling and marketing expenses in the statements of operations and comprehensive loss.

Thyroid Cytopathology Partners

Thyroid Cytopathology Partners	12 Months Ended
	Dec. 31, 2015
Thyroid Cytopathology Partners.
Thyroid Cytopathology Partners	14. Thyroid Cytopathology Partners In 2010, the Company entered into an arrangement with Pathology Resource Consultants, P.A. ("PRC") to set up and manage a specialized pathology practice to provide testing services to the Company. There is no direct monetary compensation from the Company to PRC as a result of this arrangement. The Company's service agreement is with the specialized pathology practice, Thyroid Cytopathology Partners, ("TCP"), and is effective through December 31, 2015, and thereafter automatically renews every year unless either party provides notice of intent not to renew at least 12 months prior to the end of the then-current term. Under the service agreement, the Company pays TCP based on a fixed price per test schedule, which is reviewed periodically for changes in market pricing. Subsequent to December 2012, an amendment to the service agreement allows TCP to use a portion of the Company's facility in Austin, Texas. The Company does not have an ownership interest in or provide any form of financial or other support to TCP. The Company has concluded that TCP represents a variable interest entity and that the Company is not the primary beneficiary as it does not have the ability to direct the activities that most significantly impact TCP's economic performance. Therefore, the Company does not consolidate TCP. All amounts paid to TCP under the service agreement are expensed as incurred and included in cost of revenue in the statements of operations and comprehensive loss. The Company incurred $4.7 million, $4.0 million and $3.2 million in the years ended December 31, 2015, 2014 and 2013, respectively, in cytopathology testing and evaluation services expenses with TCP. The Company's outstanding obligations to TCP for cytopathology testing services were $820,000 and $1.1 million as of December 31, 2015 and 2014, respectively, and are included in accounts payable in the Company's balance sheets. TCP reimburses the Company for a proportionate share of the Company's rent and related operating expense costs for the leased facility. TCP's portion of rent and related operating expense costs for the shared space at the Austin, Texas facility was $90,000, $86,000 and $49,000 for the years ended December 31, 2015, 2014 and 2013 and is included other income, net in the Company's statements of operations and comprehensive loss.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2015
Income Taxes
Income Taxes	15. Income Taxes The Company generated a pretax loss of $33.7 million, $29.4 million and $25.6 million in the United States for the years ended December 31, 2015, 2014 and 2013, respectively. Since inception, the Company has not generated any pretax income or loss outside of the United States. The Company recorded no provision for income taxes during the year ended December 31, 2015, 2014 or 2013. The Company follows FASB ASC No. 740, Income Taxes for the Computation and Presentation of its Tax Provision. The following table presents a reconciliation of the tax expense computed at the statutory federal rate and the Company's tax expense for the period presented (in thousands of dollars): Year Ended December, 31, 2015 2014 2013 U.S. federal taxes at statutory rate $ ) $ ) $ ) State tax (net of federal benefit) ) Permanent differences Incentive stock options Tax credits ) ) ) Change in valuation allowance ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ — $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred income taxes reflect the net tax effects of temporary differences between the carrying amounts of assets and liabilities for financial reporting purposes and the amounts used for income tax purposes. Significant components of the Company's deferred tax assets and liabilities are as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Deferred tax assets: Net operating loss carryforwards $ Research and development credits Stock-based compensation Genzyme co-promotion agreement Accruals, deferred rent and other ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross deferred tax assets Valuation allowance ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: Property and equipment ) ) ) In-process research and development ) ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross deferred tax liabilities ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax liabilities ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred taxes $ — $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes , related to balance sheet classification of deferred taxes. The ASU requires that deferred tax assets and liabilities be classified as noncurrent in the statement of financial position, thereby simplifying the current guidance that requires an entity to separate deferred assets and liabilities into current and noncurrent amounts. The ASU will be effective for the Company beginning in the first quarter of fiscal year 2018 though early adoption is permitted. The Company has early-adopted the ASU as of December 31, 2015 and its statement of financial position as of this date reflects the revised classification of current deferred tax assets and liabilities as noncurrent. The Company has early-adopted this ASU prospectively and prior periods have not been retrospectively adjusted. There is no other impact on the Company's financial statements of early-adopting the ASU. The Company has established a full valuation allowance against its net deferred tax assets due to the uncertainty surrounding realization of such assets. The valuation allowance increased $11.7 million, $10.6 million and $8.1 million during the years ended December 31, 2015, 2014 and 2013, respectively. As of December 31, 2015, the Company had net operating loss carryforwards of approximately $143.8 million and $53.8 million available to reduce future taxable income, if any, for federal and state income tax purposes, respectively. Of these amounts, $1.6 million represent federal and state tax deductions from stock-based compensation, which will be recorded as an adjustment to additional paid-in capital when they reduce tax payable. The U.S. federal net operating loss carryforwards will begin to expire in 2026 while for state purposes, the net operating losses will begin to expire in 2016. As of December 31, 2015, the Company had net credit carryforwards of approximately $2.7 million and $2.1 million available to reduce future taxable income, if any, for federal and state income tax purposes, respectively. The federal credit carryforwards begin to expire in 2028. California credits have no expiration date. Other state credit carryforwards begin to expire in 2023. On December 18, 2015, The Consolidated Appropriations Act of 2014 was signed into law, which retroactively reinstated and made permanent the federal research tax credit provisions from January 1, 2015 through December 31, 2015. The Internal Revenue Code of 1986, as amended, imposes restrictions on the utilization of net operating losses and tax credits in the event of an "ownership change" of a corporation. Accordingly, a company's ability to use net operating losses and tax credits may be limited as prescribed under Internal Revenue Code Section 382 and 383 ("IRC Section 382"). Events which may cause limitations in the amount of the net operating losses or tax credits that the Company may use in any one year include, but are not limited to, a cumulative ownership change of more than 50% over a three-year period. Utilization of the federal and state net operating losses may be subject to substantial annual limitation due to the ownership change limitations provided by the IRC Section 382 rules and similar state provisions. In the event the Company has any changes in ownership, net operating losses and research and development credit carryovers could be limited and may expire unutilized. Uncertain Tax Positions As of December 31, 2015, the Company had unrecognized tax benefits of $1.9 million, none of which would currently affect the Company's effective tax rate if recognized due to the Company's deferred tax assets being fully offset by a valuation allowance. The Company does not anticipate that the amount of unrecognized tax benefits relating to tax positions existing at December 31, 2015 will significantly increase or decrease within the next 12 months. A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Unrecognized tax benefits, beginning of period $ $ $ Gross increases—tax position in prior period — Gross decreases—tax position in prior period — — — Gross increases—current period tax position Lapse of statue of limitations — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized tax benefits, end of period $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ It is the Company's policy to include penalties and interest expense related to income taxes as a component of other income (expense), net, and interest expense, respectively, as necessary. There was no interest expense or penalties related to unrecognized tax benefits recorded through December 31, 2015. The Company's major tax jurisdictions are the United States and California. All of the Company's tax years will remain open for examination by the Federal and state tax authorities for three and four years, respectively, from the date of utilization of the net operating loss or research and development credit. The Company does not have any tax audits pending.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2015
401(k) Plan
401(k) Plan	16. 401(k) Plan The Company sponsors a 401(k) defined contribution plan covering all employees. Employer contributions to the plan were $103,000 for the year ended December 31, 2015. There were no employer contributions to the plan in the years ended December 31, 2014 and 2013.

Subsequent Event

Subsequent Event	12 Months Ended
	Dec. 31, 2015
Subsequent Event
Subsequent Event	17. Subsequent Event On March 9, 2016, the Company gave Genzyme notice of termination of the Amended Agreement effective September 9, 2016. There is no impact to the Company's financial statements as of December 31, 2015 as a result of this notice of termination.

Selected Quarterly Financial Da

Selected Quarterly Financial Data (Unaudited)	12 Months Ended
	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited)
Selected Quarterly Financial Data (Unaudited)	18. Selected Quarterly Financial Data (Unaudited) The following table presents selected unaudited financial data for each of the eight quarters in the two-year period ended December 31, 2015. The Company believes this information reflects all recurring adjustments necessary to fairly present this information when read in conjunction with the Company's financial statements and the related notes. Net loss per common share, basic and diluted, for the four quarters of each fiscal year may not sum to the total for the fiscal year because of the different number of shares outstanding during each period. The results of operations for any quarter are not necessarily indicative of the results to be expected for any future period (in thousands of dollars, except for share and per share data): Quarter Ended March 31 June 30 September 30 December 31 2015: Total revenues $ $ $ $ Net loss ) ) ) ) Net loss per common share, basic and diluted ) ) ) ) Shares used to compute net loss per common share, basic and diluted 2014: Total revenues $ $ $ $ Net loss ) ) ) ) Net loss per common share, basic and diluted ) ) ) ) Shares used to compute net loss per common share, basic and diluted

Summary of Significant Accoun26

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2015
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation The Company's financial statements have been prepared in accordance with accounting principles generally accepted in the United States ("GAAP"). The financial statements include the accounts of the Company and its former wholly-owned subsidiary, which was dissolved in June 2015. For periods prior to the subsidiary dissolution, all intercompany accounts and transactions were eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant items subject to such estimates include: revenue recognition; contractual allowances; allowance for doubtful accounts; the useful lives of property and equipment; the recoverability of long-lived assets; the estimation of the fair value of intangible assets; the determination of fair value of the Company's common stock prior to the Company's IPO; stock options; preferred stock liability; income tax uncertainties, including a valuation allowance for deferred tax assets; and contingencies. The Company bases these estimates on historical and anticipated results, trends, and various other assumptions that the Company believes are reasonable under the circumstances, including assumptions as to future events. These estimates form the basis for making judgments about the carrying values of assets and liabilities and recorded revenue and expenses that are not readily apparent from other sources. Actual results could differ from those estimates and assumptions.
Liquidity	Liquidity The Company has incurred net losses since its inception and expects to incur additional losses in 2016 and in future years. As of December 31, 2015, the Company had an accumulated deficit of $148.7 million. The Company may never achieve revenue sufficient to offset its expenses. The Company believes its cash and cash equivalents of $39.1 million as of December 31, 2015 and its revenue from sales in 2016 will be sufficient to meet its anticipated cash requirements for at least the next 12 months. In April 2015, the Company issued and sold 4,907,975 shares of its common stock in a private placement, at a price of $8.15 per share. The Company received $37.3 million in net proceeds, after deducting expenses of $2.7 million. If the Company is not able to generate revenue to finance its cash requirements, the Company will need to finance future cash needs primarily through public or private equity offerings, debt financings, borrowings or strategic collaborations or licensing arrangements. If the Company is not able to secure additional funding when needed, on acceptable terms, it may have to delay, reduce the scope of or eliminate one or more research and development programs or selling and marketing initiatives which may have a material adverse effect on the Company's business, results of operations, financial condition and/or its ability to fund its scheduled obligations on a timely basis or at all.
Concentrations of Credit Risk and Other Risks and Uncertainties	Concentrations of Credit Risk and Other Risks and Uncertainties The Company's cash and cash equivalents are deposited with one major financial institution in the United States, as required by the loan and security agreement discussed in Note 8. Deposits in this institution may exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents. Several of the components of the Company's sample collection kit and test reagents are obtained from single-source suppliers. If these single-source suppliers fail to satisfy the Company's requirements on a timely basis, it could suffer delays in being able to deliver its diagnostic solutions, a possible loss of revenue, or incur higher costs, any of which could adversely affect its operating results. The Company is also subject to credit risk from its accounts receivable related to its sales. The Company generally does not perform evaluations of customers' financial condition and generally does not require collateral. Through December 31, 2015, all of the Company's revenue have been derived from the sale of Afirma. To date, Afirma has been delivered primarily to physicians in the United States. The Company's third-party payers in excess of 10% of revenue and their related revenue as a percentage of total revenue were as follows: Year Ended December 31, 2015 2014 2013 Medicare % % % United Healthcare % % % Aetna % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ As the number of payers reimbursing for Afirma increases, the percentage of revenue derived from Medicare and other significant third-party payers has changed and will continue to change as a percentage of total revenue. The Company's significant third-party payers and their related accounts receivable balance at December 31, 2015 and 2014 as a percentage of total accounts receivable are as follows: December 31, 2015 2014 Medicare % % United Healthcare % % Aetna % % No other third-party payer represented more than 10% of the Company's accounts receivable balances as of those dates.
Cash Equivalents	Cash Equivalents Cash equivalents consist of short-term, highly liquid investments with original maturities of three months or less from the date of purchase. Cash equivalents consist of amounts invested in a money market account primarily consisting of U.S. Treasury reserves.
Restricted Cash	Restricted Cash The Company had deposits of $118,000 as of December 31, 2015 and December 31, 2014, restricted from withdrawal and held by a bank in the form of collateral for irrevocable standby letters of credit totaling $118,000 held as security for the lease of the Company's headquarters and laboratory facilities in South San Francisco that expires March 31, 2016. This restricted cash is included in current assets as of December 31, 2015 and in long-term assets as of December 31, 2014. The Company also had deposits of $603,000 included in long-term assets as of December 31, 2015, restricted from withdrawal and held by a bank in the form of collateral for an irrevocable standby letter of credit held as security for the lease of the Company's new South San Francisco facility signed in April 2015. The Company reserved $70,000 in cash as of December 31, 2014 to cover liabilities associated with the acquisition of Allegro as discussed in Note 4. This amount was paid in March 2015.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company estimates an allowance for doubtful accounts against its individual accounts receivable based on estimates of expected reimbursement consistent with historical payment experience in relation to the amounts billed. Bad debt expense is included in general and administrative expense on the Company's statements of operations and comprehensive loss. Accounts receivable are written off against the allowance when there is substantive evidence that the account will not be paid. The balance of allowance for doubtful accounts as of December 31, 2015 and 2014, including charges to bad debt expense and write-offs, net of recoveries, was as follows (in thousands of dollars): As of December 31, 2015 2014 Beginning balance $ $ Charged to expense Write-offs, net of recoveries ) ) ​ ​ ​ ​ ​ ​ ​ ​ Ending balance $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Supplies Inventory	Supplies Inventory Supplies inventory consists of test reagents and other consumables primarily used in the sample collection kits and in cytopathology and GEC test processing and are valued at the lower of cost or market value. Cost is determined using actual costs on a first-in, first-out basis.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the assets, generally between three and five years. Leasehold improvements are amortized using the straight-line method over the shorter of the estimated useful life of the asset or the term of the lease. Maintenance and repairs are charged to expense as incurred, and improvements and betterments are capitalized. When assets are retired or otherwise disposed of, the cost and accumulated depreciation are removed from the balance sheet and any resulting gain or loss is reflected in the statements of operations and comprehensive loss in the period realized.
Internal-use Software	Internal-use Software The Company capitalizes costs incurred in the application development stage to design and implement the software used in the tracking and reporting of laboratory activity. Costs incurred in the development of application software are capitalized and amortized over an estimated useful life of three years on a straight-line basis. The total cost, accumulated depreciation and net book value of internal-use software was $1.3 million, $534,000 and $744,000, respectively, as of December 31, 2015, and was $927,000, $330,000 and $597,000, respectively, as of December 31, 2014, and are included in property and equipment in the Company's balance sheets. During the years ended December 31, 2015 and 2014, the Company capitalized $352,000 and $445,000, respectively, of software development costs. Amortization expense totaled $204,000, $135,000 and $108,000 in the years ended December 31, 2015, 2014 and 2013, respectively.
Business Combination	Business Combination The Company accounts for acquisitions using the acquisition method of accounting which requires the recognition of tangible and identifiable intangible assets acquired and liabilities assumed at their estimated fair values as of the business combination date. The Company allocates any excess purchase price over the estimated fair value assigned to the net tangible and identifiable intangible assets acquired and liabilities assumed to goodwill. Transaction costs are expensed as incurred in general and administrative expenses. Results of operations and cash flows of acquired companies are included in the Company's operating results from the date of acquisition.
Finite-lived Intangible Assets	Finite-lived Intangible Assets Finite-lived intangible assets relates to intangible assets reclassified from indefinite-lived intangible assets, following the launch of Percepta in April 2015. The Company amortizes finite-lived intangible assets using the straight-line method over their estimated useful life. The estimated useful life of 15 years was used for the intangible asset related to the Percepta test based on management's estimate of product life, product life of other diagnostic tests and patent life. The Company tests this finite-lived intangible asset for impairment when events or circumstances indicate a reduction in the fair value below its carrying amount. There was no impairment for the year ended December 31, 2015.
Indefinite-lived Intangible Assets - In-process Research and Development	Indefinite-lived Intangible Assets—In-process Research and Development The Company's indefinite-lived intangible assets are comprised of acquired in-process research and development ("IPR&D"). The fair value of IPR&D acquired through a business combination is capitalized as an indefinite-lived intangible asset until the completion or abandonment of the related research and development activities. When research and development is complete, the associated assets are amortized on a straight-line basis over their estimated useful lives. IPR&D is tested for impairment annually or more frequently if events or circumstances indicate that the fair value may be below the carrying value of the asset. The Company recognizes an impairment loss when the total of estimated future undiscounted cash flows expected to result from the use of the asset and its eventual disposition are less than its carrying amount. Impairment, if any, would be assessed using discounted cash flows or other appropriate measures of fair value. There were no impairments for the years ended December 31, 2015 and 2014.
Goodwill	Goodwill Goodwill, derived from the Company's acquisition of Allegro, is reviewed for impairment on an annual basis or more frequently if events or circumstances indicate that it may be impaired. The Company's goodwill evaluation is based on both qualitative and quantitative assessments regarding the fair value of goodwill relative to its carrying value. The Company has determined that it operates in a single segment and has a single reporting unit associated with the development and commercialization of diagnostic products. In the event the Company determines that it is more likely than not the carrying value of the reporting unit is higher than its fair value, quantitative testing is performed comparing recorded values to estimated fair values. If impairment is present, the impairment loss is measured as the excess of the recorded goodwill over its implied fair value. The Company performs its annual evaluation of goodwill during the fourth quarter of each fiscal year. There were no impairments for the years ended December 31, 2015 and 2014.
Derivative Liability	Derivative Liability The Company accounts for derivative financial instruments as either equity or liabilities based upon the characteristics and provisions of each instrument. The Company recorded the preferred stock liability incurred in connection with its Series C convertible preferred stock and the preferred stock warrant liability related to the issuance of a warrant for Series C convertible preferred stock, each as a derivative financial instrument liability at their fair value on the date of issuance, and the Company re-measured them on each subsequent balance sheet date. The changes in fair value were recognized as a gain or loss from the adjustment to other income (expense), net, in the statements of operations and comprehensive loss. The Company estimated the fair value of this liability using option-pricing models that include assumptions for future financings, expected volatility, expected life, yield and risk-free interest rate. The preferred stock liability was extinguished in June 2013. The warrant to purchase Series C convertible preferred stock was converted into a warrant to purchase the Company's common stock as of the closing of its IPO and was exercised through a cashless exercise in March 2014.
Bonus Accruals	Bonus Accruals The Company accrues for liabilities under discretionary employee and executive bonus plans. These estimated compensation liabilities are based on progress against corporate objectives approved by the Board of Directors, compensation levels of eligible individuals, and target bonus percentage levels. The Board of Directors and the Compensation Committee of the Board of Directors review and evaluate the performance against these objectives and ultimately determine what discretionary payments are made. The Company accrued $2.1 million and $1.1 million as of December 31, 2015 and 2014, respectively, for liabilities associated with these employee and executive bonus plans which are included in accrued liabilities in the Company's balance sheets.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying amounts of certain financial instruments including cash and cash equivalents, accounts receivable, prepaid expenses and other current assets, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Revenue Recognition	Revenue Recognition The Company recognizes revenue in accordance with the provision of ASC 954-605, Health Care Entities—Revenue Recognition. The Company's revenue is generated from the provision of diagnostic services using the Afirma solution and the service is completed upon the delivery of test results to the prescribing physician, at which time the Company bills for the service. The Company recognizes revenue related to billings for Medicare and commercial payers on an accrual basis, net of contractual and other adjustments, when amounts that will ultimately be realized can be estimated. Contractual and other adjustments represent the difference between the list price (the billing rate) and the estimated reimbursement rate for each payer. Upon ultimate collection, the amount received from Medicare and commercial payers where reimbursement was estimated is compared to previous estimates and, if necessary, the contractual allowance is adjusted accordingly. Until a contract has been negotiated with a commercial payer or governmental program, the Afirma solution may or may not be covered by these entities' existing reimbursement policies. In addition, patients do not enter into direct agreements with the Company that commit them to pay any portion of the cost of the tests in the event that their insurance declines to reimburse the Company. In the absence of an agreement with the patient or other clearly enforceable legal right to demand payment from the patient, the related revenue is only recognized upon the earlier of payment notification, if applicable, or cash receipt. The estimates of amounts that will ultimately be realized requires significant judgment by management. Some patients have out-of-pocket costs for amounts not covered by their insurance carrier, and the Company may bill the patient directly for these amounts in the form of co-payments and co-insurance in accordance with their insurance carrier and health plans. Some payers may not cover the Company's GEC as ordered by the prescribing physician under their reimbursement policies. The Company pursues reimbursement from such patients on a case-by-case basis. In the absence of contracted reimbursement coverage or the ability to estimate the amount that will ultimately be realized for the Company's services, revenue is recognized upon the earlier of receipt of third-party payer notification of payment or when cash is received. Revenue recognized when cash is received and on an accrual basis for the years ended December 31, 2015, 2014 and 2013 was as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Revenue recognized when cash is received $ $ $ Revenue recognized on an accrual basis ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Cost of Revenue	Cost of Revenue Cost of revenue is expensed as incurred and includes material and service costs, cytopathology testing services performed by a third-party pathology group, stock-based compensation expense, direct labor costs, equipment and infrastructure expenses associated with testing samples, shipping charges to transport samples, and allocated overhead including rent, information technology, equipment depreciation and utilities.
Research and Development	Research and Development Research and development costs are charged to operations as incurred. Research and development costs include payroll and personnel-related expenses, stock-based compensation expense, prototype materials, laboratory supplies, consulting costs, costs associated with setting up and conducting clinical studies at domestic and international sites, and allocated overhead including rent, information technology, equipment depreciation and utilities.
Income Taxes	Income Taxes The Company accounts for income taxes under the liability method. Under this method, deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to affect taxable income. Valuation allowances are established when necessary to reduce deferred tax assets to the amounts expected to be realized. The Company assesses all material positions taken in any income tax return, including all significant uncertain positions, in all tax years that are still subject to assessment or challenge by relevant taxing authorities. The Company's assessment of an uncertain tax position begins with the initial determination of the position's sustainability and is measured at the largest amount of benefit that is more-likely-than-not of being realized upon ultimate settlement. As of each balance sheet date, unresolved uncertain tax positions must be reassessed, and the Company will determine whether (i) the factors underlying the sustainability assertion have changed and (ii) the amount of the recognized tax benefit is still appropriate. The recognition and measurement of tax benefits requires significant judgment. Judgments concerning the recognition and measurement of a tax benefit may change as new information becomes available.
Stock-based Compensation	Stock-based Compensation Stock-based compensation expense for equity instruments issued to employees is measured based on the grant-date fair value of the awards. The fair value of each employee stock option is estimated on the date of grant using the Black-Scholes option-pricing model. The Company recognizes compensation costs on a straight-line basis for all employee stock-based compensation awards that are expected to vest over the requisite service period of the awards, which is generally the awards' vesting period. Forfeitures are required to be estimated at the time of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. Equity awards issued to non-employees are valued using the Black-Scholes option-pricing model and are subject to re-measurement as the underlying equity awards vest.
Net Loss per Common Share	Net Loss per Common Share Basic net loss per common share is calculated by dividing net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration of common stock equivalents. Diluted net loss per common share is computed by dividing net loss attributable to common stockholders by the weighted-average number of common share equivalents outstanding for the period determined using the treasury stock method. Potentially dilutive securities consisting of options and warrants to purchase common stock are considered to be common stock equivalents and were excluded from the calculation of diluted net loss per common share because their effect would be anti-dilutive for all periods presented.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update ("ASU") No. 2014-09, Revenue from Contracts with Customers , requiring an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The updated standard will replace most existing revenue recognition guidance in GAAP when it becomes effective and permits the use of either the retrospective or cumulative effect transition method. Adoption is permitted as early as the first quarter of 2017 and is required by the first quarter of 2018. The Company has not yet selected a transition method and are currently evaluating the potential effect of the updated standard on its financial statements. In August 2014, FASB issued ASU No. 2014-15, Presentation of Financial Statements Going Concern—Disclosure of Uncertainties about an Entity's Ability to Continue as a Going Concern . The amendments require management to assess an entity's ability to continue as a going concern by incorporating and expanding upon certain principles that are currently in U.S. auditing standards. Specifically, the amendments: (1) provide a definition of the term substantial doubt; (2) require an evaluation every reporting period including interim periods; (3) provide principles for considering the mitigating effect of management's plans; (4) require certain disclosures when substantial doubt is alleviated as a result of consideration of management's plans; (5) require an express statement and other disclosures when substantial doubt is not alleviated; and (6) require an assessment for a period of one year after the date that the financial statements are issued (or available to be issued). ASU 2014-15 will be effective for annual periods ending after December 15, 2016 and interim periods within annual periods beginning after December 15, 2016 with early adoption permitted. ASU 2014-15 will be effective for the Company beginning with its annual report for fiscal 2016 and interim periods thereafter. The Company does not anticipate that the adoption of this ASU will have a significant impact on its financial statements. In April 2015, the FASB issued ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs , to require debt issuance costs to be presented as an offset against debt outstanding. The update does not change current guidance on the recognition and measurement of debt issuance costs. The ASU is effective for interim and annual periods beginning after December 15, 2015. Adoption of the ASU is retrospective to each prior period presented. The Company does not anticipate that the adoption of this ASU will have a significant impact on its balance sheet. In November 2015, the FASB issued ASU 2015-17, Balance Sheet Classification of Deferred Taxes , related to balance sheet classification of deferred taxes. The ASU requires that deferred tax assets and liabilities be classified as noncurrent in the statement of financial position, thereby simplifying the current guidance that requires an entity to separate deferred assets and liabilities into current and noncurrent amounts. The ASU will be effective for the Company beginning in the first quarter of fiscal year 2018 though early adoption is permitted. The Company has early-adopted the ASU as of December 31, 2015 and its statement of financial position as of this date reflects the revised classification of current deferred tax assets and liabilities as noncurrent. The Company has early-adopted this ASU prospectively and prior periods have not been retrospectively adjusted. There is no other impact on the Company's financial statements of early-adopting the ASU.

Summary of Significant Accoun27

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2015
Concentration Risk
Schedule of balance of allowance for doubtful accounts, including charges to bad debt expense and write-offs, net of recoveries	The balance of allowance for doubtful accounts as of December 31, 2015 and 2014, including charges to bad debt expense and write-offs, net of recoveries, was as follows (in thousands of dollars): As of December 31, 2015 2014 Beginning balance $ $ Charged to expense Write-offs, net of recoveries ) ) ​ ​ ​ ​ ​ ​ ​ ​ Ending balance $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Revenue Recognition
Schedule of Revenue recognized when cash is received and on an accrual basis	Revenue recognized when cash is received and on an accrual basis for the years ended December 31, 2015, 2014 and 2013 was as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Revenue recognized when cash is received $ $ $ Revenue recognized on an accrual basis ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Revenue concentration risk | Revenue
Concentration Risk
Schedule of the Company's third-party payers as a percentage of total	Year Ended December 31, 2015 2014 2013 Medicare % % % United Healthcare % % % Aetna % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ % % % ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Gross receivables concentration risk | Accounts receivable
Concentration Risk
Schedule of the Company's third-party payers as a percentage of total	December 31, 2015 2014 Medicare % % United Healthcare % % Aetna % %

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2015
Net Loss Per Share
Schedule of the calculation of basic and diluted net loss per common share	The following table presents the calculation of basic and diluted net loss per common share for the years ended December 31, 2015, 2014 and 2013 (in thousands of dollars, except share and per share amounts): Year Ended December 31, 2015 2014 2013 Net loss $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Shares used to compute net loss per common share, basic and diluted ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss per common share, basic and diluted $ ) $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share	Year Ended December 31, 2015 2014 2013 Shares of common stock subject to outstanding options Shares of common stock issuable upon exercise of warrants — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total shares of common stock equivalents ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Business Combination (Tables)

Business Combination (Tables)	12 Months Ended
	Dec. 31, 2015
Business Combination
Schedule of pro forma financial information as if the Merger had occurred as of January 1, 2013	The following pro forma financial information is based on the historical financial statements of the Company and presents the Company's results as if the Merger had occurred as of January 1, 2013 (in thousands of dollars): Year Ended December 31, 2014 2013 Revenue $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net loss $ ) $ ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Allegro
Business Combination
Schedule of acquisition consideration	The acquisition consideration was comprised of (in thousands of dollars): Stock $ Cash Payment of outstanding indebtedness ​ ​ ​ ​ ​ Total acquisition consideration $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of fair value of assets acquired and liabilities assumed	The fair value of the assets acquired and liabilities assumed at the closing date of the Merger are summarized below (in thousands of dollars): Cash and cash equivalents $ Other assets, net In-process research and development Goodwill ​ ​ ​ ​ ​ Total net assets acquired $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2015
Balance Sheet Components
Schedule of property and equipment	Property and equipment consisted of the following (in thousands of dollars): Year Ended December 31, 2015 2014 Leasehold improvements $ $ Laboratory equipment Computer equipment Software, including software developed for internal use Furniture and fixtures Construction-in-process ​ ​ ​ ​ ​ ​ ​ ​ Total property and equipment, at cost Accumulated depreciation and amortization ) ) ​ ​ ​ ​ ​ ​ ​ ​ Total property and equipment, net $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of accrued liabilities	Accrued liabilities consisted of the following (in thousands of dollars): Year Ended December 31, 2015 2014 Accrued compensation expenses $ $ Accrued Genzyme co-promotion fees Accrued other ​ ​ ​ ​ ​ ​ ​ ​ Total accrued liabilities $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2015
Fair Value Measurements
Summary of the changes in the fair value of the Company's Level 3 financial liabilities, which are measured on a recurring basis	The following table sets forth the changes in the fair value of the Company's Level III financial liabilities, which consisted of a preferred stock liability during 2013, which were measured on a recurring basis (in thousands of dollars): Year Ended December 31, 2013 Beginning balance $ Change in fair value of preferred stock liability recorded as other expense, net Settlement of preferred stock liability ) Fair value of preferred stock warrant liability Change in fair value of preferred stock warrant liability recorded as other expense, net Conversion of preferred stock warrant liability ) ​ ​ ​ ​ ​ Ending balance $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2015
Commitments and Contingencies
Schedule of future minimum lease payments under non-cancelable operating leases	Future minimum lease payments under non-cancelable operating leases as of December 31, 2015 are as follows (in thousands of dollars): Year Ending December 31, Amounts 2016 $ 2017 2018 2019 2020 Thereafter ​ ​ ​ ​ ​ Total minimum lease payments $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Debt (Tables)

Debt (Tables)	12 Months Ended
	Dec. 31, 2015
Debt
Schedule of net debt obligation	As of December 31, 2015 and 2014, the net debt obligation was as follows (in thousands of dollars): December 31, 2015 2014 Debt and unpaid accrued end-of-term payment $ $ Unamortized note discount ) ) ​ ​ ​ ​ ​ ​ ​ ​ Net debt obligation $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of future principal payments under the Amended Loan	Future principal payments under the Amended Loan are as follows (in thousands of dollars): Year ending December 31: 2016 $ — 2017 2018 ​ ​ ​ ​ ​ Total $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of interest expense on debt	Interest expense on the debt was as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Nominal interest $ $ $ Amortization of debt discount and debt issuance costs End-of-term payment interest ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) (Tables)	12 Months Ended
	Dec. 31, 2015
Stockholders' Equity (Deficit)
Schedule of reserved shares of common stock for issuance	December 31, 2015 2014 Options issued and outstanding Options available for grant under stock option plans Common Stock available for the Employee Stock Purchase Plan — ​ ​ ​ ​ ​ ​ ​ ​ Total ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of grant date fair value of the ESPP shares was calculated using Black Scholes option	December 31, 2015 Weighted-average volatility 53.57 - 58.10% Weighted-average expected term (years) 0.49 - 0.99 Risk-free interest rate 0.17 - 0.33% Expected dividend yield —

Stock Incentive Plans (Tables)

Stock Incentive Plans (Tables)	12 Months Ended
	Dec. 31, 2015
Stock incentive plans
Summary of activity under the Company's stock option plans	The following table summarizes activity under the Company's stock option plans (aggregate intrinsic value in thousands): Shares Available for Grant Stock Options Outstanding Weighted Average Exercise Price Weighted Average Remaining Contractual Life (Years) Aggregate Intrinsic Value Balance—December 31, 2014 $ $ Additional options authorized — Granted ) Canceled ) Exercised — ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance—December 31, 2015 $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Options vested and exercisable—December 31, 2015 $ $ Options vested and expected to vest—December 31, 2015 $ $
Stock-based Compensation
Stock incentive plans
Summary of share-based compensation expense	The following table summarizes stock-based compensation expense related to stock options for the years ended December 31, 2015, 2014 and 2013, and are included in the statements of operations and comprehensive loss as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Cost of revenue $ $ $ Research and development Selling and marketing General and administrative ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total stock-based compensation expense $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Stock-based Compensation, employees
Stock incentive plans
Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model	Year Ended December 31, 2015 2014 2013 Weighted-average volatility 52.56 - 68.82% 70.19 - 78.54% 80.42 - 81.41% Weighted-average expected term (years) 5.50 - 6.08 5.50 - 6.08 5.00 - 6.08 Risk-free interest rate 1.55 - 2.03% 1.66 - 2.04% 0.88 - 2.11% Expected dividend yield — — —
Stock-based Compensation, non-employees
Stock incentive plans
Schedule of assumptions used to calculate estimated grant date fair value of stock options using the Black-Scholes option-pricing valuation model	Year Ended December 31, 2015 2014 2013 Weighted-average volatility 64.72 - 74.48% 73.20 - 74.48% 77.86 - 78.14% Weighted-average expected term (years) 7.92 - 10.00 8.75 - 10.00 7.72 - 9.75 Risk-free interest rate 1.78 - 2.29% 2.09 - 2.20% 2.59 - 2.99% Expected dividend yield — — —

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2015
Income Taxes
Schedule of reconciliation of tax expense computed at the statutory federal rate and the Company's tax expense	The following table presents a reconciliation of the tax expense computed at the statutory federal rate and the Company's tax expense for the period presented (in thousands of dollars): Year Ended December, 31, 2015 2014 2013 U.S. federal taxes at statutory rate $ ) $ ) $ ) State tax (net of federal benefit) ) Permanent differences Incentive stock options Tax credits ) ) ) Change in valuation allowance ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Total $ — $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of significant components of the Company's deferred tax assets and liabilities	Significant components of the Company's deferred tax assets and liabilities are as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Deferred tax assets: Net operating loss carryforwards $ Research and development credits Stock-based compensation Genzyme co-promotion agreement Accruals, deferred rent and other ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross deferred tax assets Valuation allowance ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax assets ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Deferred tax liabilities: Property and equipment ) ) ) In-process research and development ) ) — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Gross deferred tax liabilities ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred tax liabilities ) ) ) ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Net deferred taxes $ — $ — $ — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​
Schedule of reconciliation of the beginning and ending amount of unrecognized tax benefits	A reconciliation of the beginning and ending amount of unrecognized tax benefits is as follows (in thousands of dollars): Year Ended December 31, 2015 2014 2013 Unrecognized tax benefits, beginning of period $ $ $ Gross increases—tax position in prior period — Gross decreases—tax position in prior period — — — Gross increases—current period tax position Lapse of statue of limitations — — — ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Unrecognized tax benefits, end of period $ $ $ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

Selected Quarterly Financial 37

Selected Quarterly Financial Data (Unaudited) (Tables)	12 Months Ended
	Dec. 31, 2015
Selected Quarterly Financial Data (Unaudited)
Schedule of selected quarterly financial data (unaudited)	The results of operations for any quarter are not necessarily indicative of the results to be expected for any future period (in thousands of dollars, except for share and per share data): Quarter Ended March 31 June 30 September 30 December 31 2015: Total revenues $ $ $ $ Net loss ) ) ) ) Net loss per common share, basic and diluted ) ) ) ) Shares used to compute net loss per common share, basic and diluted 2014: Total revenues $ $ $ $ Net loss ) ) ) ) Net loss per common share, basic and diluted ) ) ) ) Shares used to compute net loss per common share, basic and diluted

Organization and Description 38

Organization and Description of Business (Details) - USD ($) $ / shares in Units, $ in Millions	Nov. 04, 2013	Dec. 31, 2013	Dec. 31, 2015	Apr. 30, 2015	Dec. 31, 2014
IPO
Initial Public Offering
Net proceeds from issuance of common stock in IPO	$ 59.2
Underwriting discounts and commissions	4.6
Offering expenses	$ 2.5
Common Stock
Initial Public Offering
Number of shares issued		5,100,351
Share Price			$ 7.20		$ 9.66
Common stock issued on automatic conversion of outstanding convertible preferred stock (in shares)	14,997,312	14,997,312
Common Stock | IPO
Initial Public Offering
Number of shares issued	5,100,351
Share Price	$ 13
Common stock issued on automatic conversion of outstanding convertible preferred stock (in shares)	14,997,312
Common Stock | Private placement
Initial Public Offering
Share Price				$ 8.15

Summary of Significant Accoun39

Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	12 Months Ended
	Apr. 30, 2015	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Liquidity
Accumulated deficit		$ (148,726)	$ (115,022)
Cash and cash equivalents		39,084	$ 35,014	$ 71,220	$ 14,002
Net proceeds from sale of common stock in private placement		$ 37,258
Common Stock
Liquidity
Number of common stock issued and sold in private placement		4,907,975
Share Price		$ 7.20	$ 9.66
Common Stock | Private placement
Liquidity
Number of common stock issued and sold in private placement	4,907,975
Share Price	$ 8.15
Net proceeds from sale of common stock in private placement	$ 37,300
Agent fees and other expenses	$ 2,700

Summary of Significant Accoun40

Summary of Significant Accounting Policies - Credit Risk, Restricted Cash, and Allowance for Doubtful Accounts (Details)	12 Months Ended
	Dec. 31, 2015USD ($)Institution	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Concentrations of Credit Risk and Other Risks and Uncertainties
Number of major financial institutions with which the company's cash and cash equivalents are deposited | Institution	1
Restricted Cash
Cash reserved to cover liabilities associated with Merger	$ 118,000	$ 70,000
Long term deposit consisting of letter of credit serving as security for lease	603,000	118,000
Activity of allowance for doubtful accounts
Beginning balance	84,000	107,000
Charged to expense	105,000	54,000	$ 109,000
Write-offs, net of recoveries	72,000	77,000
Ending balance	117,000	84,000	$ 107,000
Headquarters and laboratory facilities, South San Francisco, Lease expiring 2016
Restricted Cash
Cash reserved to cover liabilities associated with Merger	118,000
Long term deposit consisting of letter of credit serving as security for lease		$ 118,000
Amount held as security for lease	118,000
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Restricted Cash
Long term deposit consisting of letter of credit serving as security for lease	603,000
Amount held as security for lease	$ 603,000
Revenue | Revenue concentration risk
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	49.00%	55.00%	59.00%
Revenue | Revenue concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	26.00%	26.00%	32.00%
Revenue | Revenue concentration risk | United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	14.00%	18.00%	18.00%
Revenue | Revenue concentration risk | Aetna
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	9.00%	11.00%	9.00%
Accounts receivable | Gross receivables concentration risk | Medicare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	31.00%	64.00%
Accounts receivable | Gross receivables concentration risk | United Healthcare
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	25.00%	14.00%
Accounts receivable | Gross receivables concentration risk | Aetna
Concentrations of Credit Risk and Other Risks and Uncertainties
Concentrations of credit risk (as a percent)	23.00%	12.00%

Summary of Significant Accoun41

Summary of Significant Accounting Policies - Property and Equipment and Internal-use Software (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Internal-use Software
Total cost	$ 15,754,000	$ 8,151,000
Accumulated depreciation	5,440,000	3,990,000
Net book value	$ 10,314,000	4,161,000
Minimum
Property and Equipment and Internal-use Software
Estimated useful life	3 years
Maximum
Property and Equipment and Internal-use Software
Estimated useful life	5 years
Capitalized software
Property and Equipment and Internal-use Software
Estimated useful life	3 years
Internal-use Software
Total cost	$ 1,300,000	927,000
Accumulated depreciation	534,000	330,000
Net book value	744,000	597,000
Capitalized costs	352,000	445,000
Amortization expense	$ 204,000	$ 135,000	$ 108,000

Summary of Significant Accoun42

Summary of Significant Accounting Policies - Intangible Assets, Bonus Accruals, and Revenue Recongition (Details) - USD ($)	1 Months Ended	3 Months Ended								12 Months Ended
	Apr. 30, 2014	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Finite-lived Intangible Assets
Useful life	15 years
Finite-lived intangible assets, impairment										$ 0
Indefinite-lived Intangible Assets
Indefinite-lived assets, other than goodwill, impairment										0	$ 0
Goodwill
Goodwill impairment										0	0
Bonus Accruals
Accrued liabilities associated with employee and executive bonus plans		$ 2,100,000				$ 1,100,000				2,100,000	1,100,000
Revenue Recognition
Revenue recognized when cash is received										22,460,000	25,645,000	$ 14,586,000
Revenue recognized on an accrual basis										27,043,000	12,545,000	7,298,000
Total		$ 14,042,000	$ 12,335,000	$ 11,908,000	$ 11,218,000	$ 12,199,000	$ 9,838,000	$ 8,677,000	$ 7,476,000	$ 49,503,000	$ 38,190,000	$ 21,884,000

Net Loss Per Share (Details)

Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Calculation of basic and diluted net loss per common share
Net loss	$ (8,013)	$ (8,945)	$ (9,136)	$ (7,610)	$ (8,142)	$ (7,902)	$ (6,655)	$ (6,674)	$ (33,704)	$ (29,373)	$ (25,580)
Shares use to compute net loss per common share, basic and diluted (in shares)	27,672,806	27,640,806	26,048,934	22,539,723	22,508,250	21,648,660	21,237,196	21,148,342	25,994,193	21,639,374	4,158,664
Net loss per common share, basic and diluted (in dollars per share)	$ (0.29)	$ (0.32)	$ (0.35)	$ (0.34)	$ (0.36)	$ (0.37)	$ (0.31)	$ (0.32)	$ (1.30)	$ (1.36)	$ (6.15)
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options									4,179,521	3,249,469	2,384,088
Options
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options									4,179,521	3,249,469	2,359,287
Common Stock Warrants
Outstanding shares of common stock equivalents that have been excluded from diluted net loss per common share
Shares of common stock subject to outstanding options											24,801

Business Combination (Details)

Business Combination (Details) - USD ($)	1 Months Ended		12 Months Ended
	Sep. 30, 2014	Apr. 30, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Sep. 16, 2014
Fair value of the assets acquired and liabilities assumed:
Goodwill			$ 1,057,000	$ 1,057,000
Useful life		15 years
Amortization of IPR&D			800,000
Pro-Forma Financial Information
Revenue				38,190,000	$ 21,884,000
Net loss				(29,090,000)	(28,605,000)
Allegro
Business Combination
Number of Allegro shares received for each share of common stock issued and outstanding of a wholly-owned subsidiary of the Company	1
Conversion right, number of shares	964,377
Conversion right, cash	$ 2,700,000
Outstanding indebtedness settled in cash	4,300,000
Acquisition-related costs	500,000
Transaction bonuses and severance payments	1,200,000
Acquisition consideration
Stock	10,078,000
Cash	2,725,000
Payment of outstanding indebtedness	4,290,000
Total acquisition consideration	17,093,000
Closing price of Company's common stock						$ 10.45
Fair value of the assets acquired and liabilities assumed:
Cash and cash equivalents	29,000
Other assets, net	7,000
In-process research and development	16,000,000
Goodwill	1,057,000
Total acquisition consideration	$ 17,093,000
Discount rate (as a percent)	18.50%
Allegro | Transaction bonus and other payments to employees and acquisition related costs
Pro-Forma Financial Information
Net loss				2,200,000
Allegro | Interest expense related to indebtedness of acquired entity
Pro-Forma Financial Information
Net loss				$ 2,300,000	$ 4,500,000
Allegro | IPR&D
Fair value of the assets acquired and liabilities assumed:
Accumulated amortization			800,000
Annual amortization expense expected to be recognized			800,000
Amortization expense over each of the next five years			$ 1,100,000
Allegro | IPR&D | Maximum
Fair value of the assets acquired and liabilities assumed:
Useful life	15 years

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Property and Equipment, Net
Total property and equipment, at cost	$ 15,754	$ 8,151
Accumulated depreciation and amortization	(5,440)	(3,990)
Total property and equipment, net	10,314	4,161
Depreciation and amortization expense	2,254	1,175	$ 999
Leasehold improvements
Property and Equipment, Net
Total property and equipment, at cost	789	788
Laboratory equipment
Property and Equipment, Net
Total property and equipment, at cost	5,501	4,199
Computer equipment
Property and Equipment, Net
Total property and equipment, at cost	1,046	875
Software, including software developed for internal use
Property and Equipment, Net
Total property and equipment, at cost	1,353	1,353
Furniture and fixtures
Property and Equipment, Net
Total property and equipment, at cost	242	197
Construction-in-process
Property and Equipment, Net
Total property and equipment, at cost	$ 6,823	$ 739

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014
Accrued Liabilities
Accrued compensation expenses	$ 4,212	$ 2,673
Accrued Genzyme co-promotion fees	2,089	3,309
Accrued other	2,388	1,869
Total accrued liabilities	$ 8,689	$ 7,851

Fair Value Measurements - Money

Fair Value Measurements - Money Market Funds (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Recurring | Level I | Money market funds
Fair value measurements
Financial Assets	$ 37.5	$ 33.2

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Level III Financial Liabilites (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2013	Dec. 31, 2013
Preferred stock liability
Changes in the fair value of the Company's Level 3 financial liabilities
Settlement of preferred stock	$ (2,700)
Recurring | Level 3
Changes in the fair value of the Company's Level 3 financial liabilities
Beginning balance		$ 583
Recurring | Level 3 | Preferred stock liability
Changes in the fair value of the Company's Level 3 financial liabilities
Settlement of preferred stock		(2,653)
Change in fair value of preferred stock liability recorded as other expense, net		2,070
Recurring | Level 3 | Preferred stock warrant liability
Changes in the fair value of the Company's Level 3 financial liabilities
Fair value of liability		175
Change in fair value of preferred stock liability recorded as other expense, net		86
Conversion of preferred stock warrant liability		$ (261)

Fair Value Measurements - Optio

Fair Value Measurements - Option-Pricing Method (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended
	Jun. 30, 2013	Nov. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Nov. 30, 2013	Jun. 17, 2013
Fair value measurements
Change in value of preferred stock liability			$ 2,070
Series C
Assumptions used to calculate fair value of preferred stock liability using the option-pricing method
Estimated fair value common stock (in dollars per share)	$ 2.40	$ 1.78			$ 13.14	$ 2.39
Preferred stock liability
Fair value measurements
Fair value of liability	$ 2,700	$ 900		$ 600
Change in value of preferred stock liability	$ 2,100			$ (300)
Assumptions used to calculate fair value of preferred stock liability using the option-pricing method
Probability of success of the second tranche (as a percent)	100.00%	100.00%
Term	1 day	8 months 1 day
Expected volatility (as a percent)	36.40%	44.00%

Commitments and Contingencies50

Commitments and Contingencies (Details)	1 Months Ended	12 Months Ended
	Apr. 30, 2015ft²	Dec. 31, 2015USD ($)item	Dec. 31, 2014USD ($)	Dec. 31, 2013USD ($)
Operating Leases
Long term deposit consisting of letter of credit serving as security for lease		$ 603,000	$ 118,000
Future minimum lease payments under non-cancelable operating leases
2,016		1,821,000
2,017		2,143,000
2,018		2,102,000
2,019		2,026,000
2,020		2,082,000
Thereafter		11,956,000
Total minimum lease payments		22,130,000
Facilities rent expense		1,900,000	852,000	$ 840,000
Expected straight-line rent expense per quarter until new headquarters is utilized		$ 500,000
Supplies Purchase Commitments
Number of suppliers with which Company has non-cancelable purchase commitment | item		2
Non-cancelable purchase commitment		$ 837,000
Headquarters and laboratory facilities, South San Francisco, Lease signed in April 2015
Operating Leases
Amount of space leased | ft²	59,000
Amount of funding provided by landlord for tenant improvements		3,300,000
Estimated amount of improvements expected in addition to landlord's tenant allowance		2,700,000
Estimated costs to complete the build-out of the facility		1,300,000
Security deposit		603,000
Long term deposit consisting of letter of credit serving as security for lease		603,000
Laboratory facilities, Austin, Texas
Operating Leases
Security deposit		$ 75,000	$ 75,000

Debt (Details)

Debt (Details)	1 Months Ended			12 Months Ended
	Nov. 30, 2015USD ($)	Dec. 31, 2014USD ($)trancheinstallment	Jun. 30, 2013USD ($)installment$ / sharesshares	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)trancheinstallment	Dec. 31, 2013USD ($)	Dec. 01, 2014USD ($)	Nov. 30, 2014USD ($)	Mar. 31, 2014USD ($)	Nov. 30, 2013USD ($)$ / shares
Debt
Amount drawn down			$ 5,000,000
Cash paid for interest on debt				$ 278,000	$ 307,000	$ 132,000
Interest expense on debt
End-of-term payment				79,000	81,000	42,000
Convertible Preferred Stock Warrants
Interest expense on debt
Exercise price of warrant to purchase shares of Series C convertible preferred stock (in dollars per share) | $ / shares			$ 7.56							$ 7.56
Number of shares for which warrant became exercisable | shares			24,801
Aggregate fair value of the warrant for the shares exercisable under the warrant			$ 175,000							$ 261,000
Amortization period of debt discount			48 months
Term Loans
Debt
Maximum borrowing capacity		$ 15,000,000	$ 10,000,000		$ 15,000,000
Amount not drawn									$ 5,000,000
Number of installments | installment		24			24
Period after which debt is repayable		24 months
Prepayment penalties for prepayment within one year of the loan origination (as a percent)		2.00%
Prepayment penalties for prepayment within two years of the loan origination (as a percent)		1.00%
Prepayment penalties for prepayment after two years of the loan origination (as a percent)		0.00%
Number of tranches | tranche		3			3
Cash paid for interest on debt		$ 14,000
End-of term payment		110,000
Amount of prepayment premium waived								$ 75,000
Balloon payment				82,000
Amount of end of term payment				$ 237,500			$ 110,000	$ 225,000
End of term payment as a percentage of total outstanding principal balance				4.75%
Third-party fees paid		45,000
Debt and unpaid accrued end-of-term payment		5,003,000		$ 5,082,000	$ 5,003,000
Unamortized note discount		(80,000)		(54,000)	(80,000)
Net debt obligation		4,923,000		5,028,000	4,923,000
Future principal payments
2,017				2,437,000
2,018				2,563,000
Total				5,000,000
Interest expense on debt
Nominal interest				253,000	296,000	158,000
Amortization of debt discount and debt issuance costs				46,000	62,000	33,000
End-of-term payment				79,000	81,000	42,000
Total				$ 378,000	439,000	$ 233,000
Term Loans | Term Loan Due 2017
Debt
Amount drawn down			$ 5,000,000
Number of installments | installment			30
Period after which debt is repayable			18 months
Interest rate (as a percent)			6.06%
Prepayment penalties for prepayment within one year of the loan origination (as a percent)			2.25%
Prepayment penalties for prepayment within two years of the loan origination (as a percent)			1.50%
Prepayment penalties for prepayment after two years of the loan origination (as a percent)			0.75%
Repayment of debt		5,000,000
Term Loans | Term Loan Tranche One
Debt
Maximum borrowing capacity		5,000,000			$ 5,000,000
Amount drawn down		$ 5,000,000
Interest rate (as a percent)		5.00%			5.00%
Term Loans | Term Loan Tranche Two
Debt
Maximum borrowing capacity		$ 5,000,000			$ 5,000,000
Amount drawn down	$ 5,000,000
Term Loans | Term Loan Tranche Three
Debt
Maximum borrowing capacity		$ 5,000,000			$ 5,000,000

Convertible Preferred Stock W52

Convertible Preferred Stock Warrant (Details) - USD ($)	1 Months Ended			12 Months Ended
	Mar. 31, 2014	Nov. 30, 2013	Jun. 30, 2013	Dec. 31, 2013	Jun. 17, 2013	Nov. 30, 2012
Convertible preferred stock warrant
Amount drawn down on term loan			$ 5,000,000
Assumptions used to calculate fair value of warrant upon issuance using Black-Scholes option-pricing valuation model
Amount of change in the fair value reported as an expense in other income (expense), net				$ 86,000
Series C
Assumptions used to calculate fair value of warrant upon issuance using Black-Scholes option-pricing valuation model
Estimated fair value common stock (in dollars per share)		$ 13.14	$ 2.40		$ 2.39	$ 1.78
Convertible Preferred Stock Warrants
Convertible preferred stock warrant
Number of shares of preferred stock that can be purchased by each warrant			49,602
Exercise price of warrant to purchase shares of Series C convertible preferred stock (in dollars per share)		$ 7.56	$ 7.56
Number of shares for which warrant became exercisable		24,801	24,801
Number of warrants exercised	24,801
Issuance of common stock on cashless exercise of warrant (in shares)	13,739
Fair value of currently exercisable portion of the warrant		$ 261,000	$ 175,000
Assumptions used to calculate fair value of warrant upon issuance using Black-Scholes option-pricing valuation model
Contractual term		7 years	7 years 3 months 18 days
Risk-free interest rate (as a percent)		2.00%	2.10%
Expected volatility (as a percent)		81.40%	73.70%
Expected dividend yield (as a percent)		0.00%	0.00%
Amount of change in the fair value reported as an expense in other income (expense), net		$ 86,000

Convertible Preferred Stock (De

Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands	Nov. 04, 2013	Jun. 30, 2013	Nov. 30, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2015	Dec. 31, 2014	Nov. 30, 2013	Jun. 17, 2013
Convertible preferred stock
Preferred stock liability valuation decrease recorded in other income (expense), net				$ (2,070)
Preferred stock liability
Assumptions used to calculate fair value of preferred stock liability using the option-pricing method
Probability of success of the second tranche (as a percent)		100.00%	100.00%
Contractual term		1 day	8 months 1 day
Expected volatility (as a percent)		36.40%	44.00%
Convertible preferred stock
Preferred stock liability		$ 2,700	$ 900		$ 600
Preferred stock liability valuation decrease recorded in other income (expense), net		(2,100)			$ 300
Preferred stock liability settled		$ (2,700)
Common Stock
Assumptions used to calculate fair value of preferred stock liability using the option-pricing method
Estimated fair value common stock (in dollars per share)						$ 7.20	$ 9.66
Convertible preferred stock
Conversion of preferred stock into common stock upon initial public offering (in shares)	14,997,312			14,997,312
Convertible Preferred Stock.
Convertible preferred stock
Convertible preferred stock converted to common stock (in shares)	59,989,268
Conversion of preferred stock into common stock upon initial public offering (in shares)				(59,989,268)
Series C
Assumptions used to calculate fair value of preferred stock liability using the option-pricing method
Estimated fair value common stock (in dollars per share)		$ 2.40	$ 1.78					$ 13.14	$ 2.39

Stockholders' Equity (Details)

Stockholders' Equity (Details)	1 Months Ended		12 Months Ended
	May. 31, 2015USD ($)shares	Apr. 30, 2015USD ($)$ / sharesshares	Dec. 31, 2015USD ($)Vote$ / sharesshares	Dec. 31, 2014$ / sharesshares
Common Stock
Authorized shares of common stock			125,000,000	125,000,000
Par value of shares of common stock (in dollars per share) | $ / shares			$ 0.001	$ 0.001
Number of votes for each share of stock | Vote			1
Dividends declared | $			$ 0
Options issued and outstanding (in shares)			4,179,521	3,249,469
Shares available for issuance			1,058,359	1,341,252
Total number of shares reserved for issuance			5,987,880	4,590,721
Net proceeds from sale of common stock in private placement | $			$ 37,258,000
Options
Common Stock
Options issued and outstanding (in shares)			4,179,521	3,249,469
Shares available for issuance			1,058,359	1,341,252
ESPP
Common Stock
Stock compensation expense | $			$ 190,000
Employee Stock Purchase Plan
Maximum offering period	12 months
Purchase period	6 months
Maximum number of shares per employee per offering period (in shares)	2,500
Maximum fair market value of shares an employee can purchase per calendar year | $	$ 25,000
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)			53.57%
Weighted-average volatility, high end of range (as a percent)			58.10%
Risk-free interest rate, low end of range (as a percent)			0.17%
Risk-free interest rate, high end of range (as a percent)			0.33%
ESPP | Minimum
Employee Stock Purchase Plan
Minimum purchase price as a percentage of fair market value	85.00%
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term			5 months 27 days
ESPP | Maximum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term			11 months 27 days
Common Stock
Common Stock
Number of common stock issued and sold in private placement			4,907,975
Share Price | $ / shares			$ 7.20	$ 9.66
Common Stock | Private placement
Common Stock
Number of common stock issued and sold in private placement		4,907,975
Share Price | $ / shares		$ 8.15
Gross proceeds from sale of common stock in private placement | $		$ 40,000,000
Net proceeds from sale of common stock in private placement | $		37,300,000
Agent fees and other expenses | $		$ 2,700,000
Common Stock | ESPP
Common Stock
Shares available for issuance			750,000

Stock Incentive Plans - Stock O

Stock Incentive Plans - Stock Option Plans (Details) - shares	1 Months Ended	12 Months Ended
	Feb. 29, 2008	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2013
Stock incentive plans
Number of shares available for issuance		1,058,359	1,341,252
Options
Stock incentive plans
Number of shares available for issuance		1,058,359	1,341,252
2008 Plan | Options | Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value	100.00%
2008 Plan | Options | Maximum
Stock incentive plans
Term of options granted	10 years
2008 Plan | Options | Newly hired employee
Stock incentive plans
Vesting period	4 years
Percentage of award vesting after one year	25.00%
2008 Plan | ISO | Minimum
Stock incentive plans
Voting power of person owning stock (as a percent)	10.00%
Option price as a percentage of estimated fair value of shares on date of grant to a person owning stock representing more than 10% of voting power of all classes of stock	110.00%
2008 Plan | ISO | Maximum
Stock incentive plans
Term of options granted to a person owning stock representing more than 10% of voting power of all classes of stock	5 years
2013 Plan
Stock incentive plans
Number of additional shares reserved for issuance				1,700,000
Maximum annual increase in outstanding shares on the last day of the immediately preceding fiscal year (as a percent)		4.00%
Number of shares available for issuance		1,058,359
2013 Plan | Options | Outside director serving as a member of Board of Directors for at least six months
Stock incentive plans
Shares granted as annual grant		10,000
2013 Plan | Options | Outside director serving as a member of Board of Directors for at least six months | Minimum
Stock incentive plans
Period for which director has to serve as board of director to receive grant to purchase shares		6 months
2013 Plan | Options | Outside director
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
2013 Plan | Options | Outside director | Maximum
Stock incentive plans
Expiration period after termination of service		12 months
2013 Plan | ISO | Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
2013 Plan | ISO | Maximum
Stock incentive plans
Term of options granted		10 years
2013 Plan | NSO | Minimum
Stock incentive plans
Minimum purchase price as a percentage of fair market value		100.00%
2013 Plan | NSO | Outside director who was not previously an employee
Stock incentive plans
Percentage of award vesting after one year		25.00%
Shares granted as initial grant		35,000
Percentage of award granted which vests on a monthly basis		0.75
Period over which remaining shares will vest on a monthly basis		3 years

Stock Incentive Plans - Activit

Stock Incentive Plans - Activity Under Stock Option Plans (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Shares Available for Grant
Balance at the beginning of the period (in shares)	1,341,252
Additional options authorized (in shares)	900,946
Granted (in shares)	(1,521,025)
Canceled (in shares)	337,186
Balance at the end of the period (in shares)	1,058,359	1,341,252
Stock Options Outstanding
Balance at beginning of the period (in shares)	3,249,469
Granted (in shares)	1,521,025
Canceled (in shares)	(337,186)
Exercised (in shares)	(253,787)
Balance at the end of the period (in shares)	4,179,521	3,249,469
Options vested and exercisable at the end of the period (in shares)	1,945,279
Options vested and expected to vest at the end of the period (in shares)	4,179,499
Weighted Average Exercise Price
Balance at beginning of the period (in dollars per share)	$ 7.59
Granted (in dollars per share)	8.72
Canceled (in dollars per share)	10.74
Exercised (in dollars per share)	2.85
Balance at the end of the period (in dollars per share)	8.03	$ 7.59
Options vested and exercisable at the end of the period (in dollars per share)	6.14
Options vested and expected to vest at the end of the period (in dollars per share)	$ 8.03
Weighted Average Remaining Contractual Life
Balance	7 years 6 months	7 years 10 months 17 days
Options vested and exercisable at the end of the period	5 years 11 months 16 days
Options vested and expected to vest at the end of the period	7 years 6 months
Aggregate Intrinsic Value
Balance at the beginning of the period (in dollars)	$ 12,400
Balance at the end of the period (in dollars)	6,511	$ 12,400
Options vested and exercisable at the end of the period (in dollars)	5,801
Options vested and expected to vest at the end of the period (in dollars)	$ 6,511

Stock Incentive Plans - Additio

Stock Incentive Plans - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock incentive plans
Weighted average fair value of options to purchase common stock granted (in dollars per share)	$ 5.12	$ 9.08	$ 4.19
Weighted average fair value of vested options (in dollars per share)	7.01	3.07	$ 2.12
Weighted average fair value of stock options exercised (in dollars per share)	$ 2	$ 1.18
Intrinsic value of stock options exercised (in dollars)	$ 1.8	$ 3.2	$ 4.9
Common Stock
Stock incentive plans
Share Price	$ 7.20	$ 9.66
Employee stock options
Stock incentive plans
Total estimated grant date fair value of options to purchase common stock vested (in dollars)	$ 5.3	$ 1.6

Stock Incentive Plans - Stock-b

Stock Incentive Plans - Stock-based Compensation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock-based compensation
Granted (in shares)	1,521,025
Stock-based Compensation
Stock-based compensation
Share-based compensation expense (in dollars)	$ 5,602	$ 3,548	$ 1,247
Unrecognized compensation expense (in dollars)	$ 10,600
Period over which unrecognized compensation expense expected to be recognized	2 years 8 months 12 days
Stock-based Compensation | Cost of revenue
Stock-based compensation
Share-based compensation expense (in dollars)	$ 100	51	34
Stock-based Compensation | Research and development
Stock-based compensation
Share-based compensation expense (in dollars)	1,178	790	250
Stock-based Compensation | Selling and marketing
Stock-based compensation
Share-based compensation expense (in dollars)	1,326	707	169
Stock-based Compensation | General and administrative
Stock-based compensation
Share-based compensation expense (in dollars)	$ 2,998	$ 2,000	$ 794
Stock-based Compensation, employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)	52.56%	70.19%	80.42%
Weighted-average volatility, high end of range (as a percent)	68.82%	78.54%	81.41%
Risk-free interest rate, low end of range (as a percent)	1.55%	1.66%	0.88%
Risk-free interest rate, high end of range (as a percent)	2.03%	2.04%	2.11%
Stock-based Compensation, employees | Minimum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	5 years 6 months	5 years 6 months	5 years
Stock-based Compensation, employees | Maximum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	6 years 29 days	6 years 29 days	6 years 29 days
Stock-based Compensation, non-employees
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average volatility, low end of range (as a percent)	64.72%	73.20%	77.86%
Weighted-average volatility, high end of range (as a percent)	74.48%	74.48%	78.14%
Risk-free interest rate, low end of range (as a percent)	1.78%	2.09%	2.59%
Risk-free interest rate, high end of range (as a percent)	2.29%	2.20%	2.99%
Stock-based Compensation, non-employees | Minimum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	7 years 11 months 1 day	8 years 9 months	7 years 8 months 19 days
Stock-based Compensation, non-employees | Maximum
Assumptions used to calculate estimated fair value of stock options using the Black-Scholes option-pricing valuation model
Weighted-average expected term	10 years	10 years	9 years 9 months

Stock Incentive Plans - Equity-

Stock Incentive Plans - Equity-based Compensation (Details) - USD ($)	1 Months Ended	12 Months Ended
	Feb. 28, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Stock-based compensation
Options granted (in shares)		1,521,025
Weighted average fair value of stock options vested (in dollars per share)		$ 7.01	$ 3.07	$ 2.12
Equity-based Compensation, executive bonuses
Stock-based compensation
Options granted (in shares)	100,498
Weighted average fair value of stock options vested (in dollars per share)	$ 2.59
Share-based compensation expense (in dollars)					$ 259,000

Genzyme Co-promotion Agreement

Genzyme Co-promotion Agreement (Details)	Jan. 01, 2015	Aug. 12, 2014	Feb. 29, 2012USD ($)	Dec. 31, 2015USD ($)$ / shares	Sep. 30, 2015USD ($)$ / shares	Jun. 30, 2015USD ($)$ / shares	Mar. 31, 2015USD ($)$ / shares	Dec. 31, 2014USD ($)$ / shares	Sep. 30, 2014USD ($)$ / shares	Jun. 30, 2014USD ($)$ / shares	Mar. 31, 2014USD ($)$ / shares	Jul. 31, 2014USD ($)	Dec. 31, 2015USD ($)$ / shares	Dec. 31, 2014USD ($)$ / shares	Dec. 31, 2013USD ($)$ / shares	Dec. 31, 2012	Feb. 27, 2014	Dec. 31, 2015USD ($)	Aug. 11, 2014	Feb. 28, 2015country	Jan. 31, 2012country
Genzyme Co-promotion Agreement
Loss from operations													$ (33,466,000)	$ (29,006,000)	$ (23,173,000)
Net loss				$ (8,013,000)	$ (8,945,000)	$ (9,136,000)	$ (7,610,000)	$ (8,142,000)	$ (7,902,000)	$ (6,655,000)	$ (6,674,000)		$ (33,704,000)	$ (29,373,000)	$ (25,580,000)
Loss per common share | $ / shares				$ (0.29)	$ (0.32)	$ (0.35)	$ (0.34)	$ (0.36)	$ (0.37)	$ (0.31)	$ (0.32)		$ (1.30)	$ (1.36)	$ (6.15)
Amortization of up-front co-promotion fee													$ 1,897,000	$ 2,269,000	$ 2,500,000
Co-promotion agreement | Genzyme
Genzyme Co-promotion Agreement
Co-promotion expenses													7,300,000	12,000,000	8,600,000
Outstanding obligation to Genzyme				$ 2,100,000				$ 6,000,000					2,100,000	6,000,000				$ 2,100,000
Amortization of up-front co-promotion fee													1,900,000	2,300,000	$ 2,500,000
Co-promotion agreement | Genzyme | Accounts payable
Genzyme Co-promotion Agreement
Outstanding obligation to Genzyme								2,700,000						2,700,000
Co-promotion agreement | Genzyme | Accrued liabilities
Genzyme Co-promotion Agreement
Outstanding obligation to Genzyme				$ 2,100,000				$ 3,300,000					$ 2,100,000	3,300,000				$ 2,100,000
Afirma thyroid diagnostic solution co-promotion agreement | Genzyme
Genzyme Co-promotion Agreement
Number of countries outside United States for exclusive promotion under the agreement | country																					40
Co-promotion fee received from Genzyme			$ 10,000,000
Co-promotion fees as a percentage of cash receipts																50.00%	40.00%	32.00%
Maximum amount to be spent by co-promoter for qualifying clinical development activities in countries that require additional testing												$ 500,000
Straight-line amortization period of co-promotion fee																			4 years
Co-promotion fees as a percentage of cash receipts for remaining periods													15.00%
Termination notification period		6 months
Afirma thyroid diagnostic solution co-promotion agreement | Genzyme | Extension of amortization period
Genzyme Co-promotion Agreement
Loss from operations													$ (600,000)	(200,000)
Net loss													$ (600,000)	$ (200,000)
Loss per common share | $ / shares													$ (0.02)	$ (0.01)
Ex-U.S. Co-Promotion Agreement | Genzyme
Genzyme Co-promotion Agreement
Number of countries outside United States for exclusive promotion under the agreement | country																				5
Co-promotion fee paid as a percentage of net revenue	25.00%
Period of agreement	5 years

Thyroid Cytopathology Partners

Thyroid Cytopathology Partners (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Thyroid Cytopathology Partners
Outstanding obligations	$ 5,085,000	$ 7,397,000
Thyroid Cytopathology Partners
Thyroid Cytopathology Partners
Notice of intent not to renew period	12 months
Expenses for cytopathology testing and evaluation services	$ 4,700,000	4,000,000	$ 3,200,000
Outstanding obligations	820,000	1,100,000
Reduction to rent expense for TCP's portion of costs for shared space	$ (90,000)	$ (86,000)	$ (49,000)

Income Taxes - Tax Effects (Det

Income Taxes - Tax Effects (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes
Pretax loss	$ 33,704	$ 29,373	$ 25,580
Provision for income taxes	0	0	0
Reconciliation of tax expense computed at the statutory federal rate and the Company's tax expense
U.S. federal taxes at statutory rate	(11,459)	(9,987)	(8,697)
State tax (net of federal benefit)	(30)	5	11
Permanent differences	96	64	790
Incentive stock options	789	672	355
Tax credits	(581)	(461)	(502)
Change in valuation allowance	11,185	9,707	8,043
Total provision for income taxes	0	0	0
Non-current deferred tax assets:
Net operating loss carryforwards	52,262	41,971	28,569
Research and development credits	2,497	1,916	1,455
Stock-based compensation	1,825	826	313
Genzyme co-promotion agreement	330	995	1,792
Accruals, deferred rent and other	4,698	3,381	705
Gross deferred tax assets	61,612	49,089	32,834
Valuation allowance	(55,101)	(43,439)	(32,819)
Net deferred tax assets	6,511	5,650	15
Deferred tax liabilities:
Property and equipment	(1,215)	(60)	(15)
In-process research and development	(5,296)	(5,590)
Gross deferred tax liabilities	(6,511)	(5,650)	(15)
Net deferred tax liabilities	(6,511)	(5,650)	(15)
Increase in valuation allowance against deferred tax assets	11,700	$ 10,600	$ 8,100
Operating loss carryforwards
Federal and state net operating loss carryforwards related to stock-based compensation	1,600
Federal
Operating loss carryforwards
Net operating loss carryforwards	143,800
State
Operating loss carryforwards
Net operating loss carryforwards	$ 53,800

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Unrecognized tax benefits, beginning of period	$ 1,571	$ 727	$ 481
Gross increases-tax position in prior period		548	68
Gross increases-current period tax position	300	296	178
Unrecognized tax benefits, end of period	1,871	$ 1,571	$ 727
Interest expense or penalties related to unrecognized tax benefits	0
Federal
Credit carryforwards
Credit carryforwards available to reduce future taxable income	2,700
State
Credit carryforwards
Credit carryforwards available to reduce future taxable income	$ 2,100

Income Taxes - Income Tax Exami

Income Taxes - Income Tax Examination (Details)	12 Months Ended
	Dec. 31, 2015
Federal
Income tax examination
Income tax examination period	3 years
State
Income tax examination
Income tax examination period	4 years

401(k) Plan (Details)

401(k) Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
401(k) Plan
Employer contributions to the plan	$ 103,000	$ 0	$ 0

Selected Quarterly Financial 66

Selected Quarterly Financial Data (Unaudited) (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Data (Unaudited)
Total revenues	$ 14,042	$ 12,335	$ 11,908	$ 11,218	$ 12,199	$ 9,838	$ 8,677	$ 7,476	$ 49,503	$ 38,190	$ 21,884
Net loss	$ (8,013)	$ (8,945)	$ (9,136)	$ (7,610)	$ (8,142)	$ (7,902)	$ (6,655)	$ (6,674)	$ (33,704)	$ (29,373)	$ (25,580)
Net loss per common share, basic and diluted	$ (0.29)	$ (0.32)	$ (0.35)	$ (0.34)	$ (0.36)	$ (0.37)	$ (0.31)	$ (0.32)	$ (1.30)	$ (1.36)	$ (6.15)
Shares use to compute net loss per common share, basic and diluted (in shares)	27,672,806	27,640,806	26,048,934	22,539,723	22,508,250	21,648,660	21,237,196	21,148,342	25,994,193	21,639,374	4,158,664