Forte Biosciences (FBRX) 10-Q 23 May 17 2017 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2017	May 18, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2017
Document Fiscal Year Focus	2,017
Document Fiscal Period Focus	Q1
Trading Symbol	TOCA
Entity Registrant Name	Tocagen Inc
Entity Central Index Key	1,419,041
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		19,807,566

CONDENSED BALANCE SHEETS (Unaud

CONDENSED BALANCE SHEETS (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Current assets:
Cash and cash equivalents	$ 6,955	$ 5,510
Marketable securities	21,930	25,735
Prepaid expenses and other current assets	1,153	1,216
Total current assets	30,038	32,461
Property and equipment, net	734	743
Other assets	3,522	2,147
Total assets	34,294	35,351
Current liabilities:
Accounts payable	947	1,666
Accrued liabilities	7,856	5,437
Notes payable, current portion	7,200	7,200
Deferred license revenue	41	45
Deferred grant funding	31	34
Total current liabilities	16,075	14,382
Notes payable, net of current portion	8,583	10,241
Convertible promissory notes payable (due to related parties of $1,299 and $1,025 at March 31, 2017 and December 31, 2016, respectively)	11,016	3,398
Convertible promissory notes subscription liability		140
Long-term portion of deferred license revenue	61	68
Preferred stock warrant liabilities	67	126
Total liabilities	35,802	28,355
Commitments and contingencies
Convertible preferred stock, $0.001 par value; 51,000,000 shares authorized at March 31, 2017 and December 31, 2016; 46,163,605 shares issued and outstanding at March 31, 2017 and December 31, 2016; aggregate liquidation preferences of $131,720 at March 31, 2017 and December 31, 2016	131,413	131,413
Stockholders’ deficit:
Common stock, $0.001 par value; 77,800,000 shares authorized at March 31, 2017 and December 31, 2016; 2,227,167 and 2,202,517 shares issued and outstanding at March 31, 2017 and December 31, 2016, respectively	2	2
Additional paid-in capital	4,151	3,581
Accumulated deficit	(137,073)	(128,000)
Accumulated other comprehensive loss	(1)
Total stockholders’ deficit	(132,921)	(124,417)
Total liabilities and stockholders’ deficit	$ 34,294	$ 35,351

CONDENSED BALANCE SHEETS (Paren

CONDENSED BALANCE SHEETS (Parenthetical) (Unaudited) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Statement Of Financial Position [Abstract]
Due to related parties	$ 1,299	$ 1,025
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	51,000,000	51,000,000
Preferred stock, shares issued	46,163,605	46,163,605
Preferred stock, shares outstanding	46,163,605	46,163,605
Preferred stock, liquidation preference	$ 131,720	$ 131,720
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	77,800,000	77,800,000
Common stock, shares issued	2,227,167	2,202,517
Common stock, shares outstanding	2,227,167	2,202,517

CONDENSED STATEMENTS OF OPERATI

CONDENSED STATEMENTS OF OPERATIONS (Unaudited) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
License revenue	$ 11,000	$ 14,000
Operating expenses:
Research and development	6,624,000	6,469,000
General and administrative	1,940,000	1,111,000
Total operating expenses	8,564,000	7,580,000
Loss from operations	(8,553,000)	(7,566,000)
Other income (expense), net:
Interest income	37,000	61,000
Interest expense (related party interest expense of $21 and $0 during the three months ended March 31, 2017 and 2016, respectively)	(616,000)	(503,000)
Change in fair value of preferred stock warrants	59,000	2,000
Total other income (expense), net	(520,000)	(440,000)
Net loss	(9,073,000)	(8,006,000)
Other comprehensive income (loss):
Net unrealized gain (loss) on investments	(1,000)	54,000
Comprehensive loss	$ (9,074,000)	$ (7,952,000)
Net loss per common share, basic and diluted	$ (4.11)	$ (3.64)
Weighted-average number of common shares outstanding, basic and diluted	2,207,747	2,198,080

CONDENSED STATEMENTS OF OPERAT5

CONDENSED STATEMENTS OF OPERATIONS (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Income Statement [Abstract]
Related party interest expense	$ 21	$ 0

CONDENSED STATEMENTS OF CASH FL

CONDENSED STATEMENTS OF CASH FLOWS (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
OPERATING ACTIVITIES
Net loss	$ (9,073)	$ (8,006)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	529	265
Depreciation	65	60
Noncash interest expense	147	140
Change in fair value of preferred stock warrants	(59)	(2)
Amortization of premium (discount) on investments, net	1	3
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	19	(412)
Accounts payable	(1,077)	495
Accrued liabilities	1,895	1,434
Deferred license revenue	(11)	(14)
Deferred grant funding	(3)	(30)
Net cash used in operating activities	(7,567)	(6,067)
INVESTING ACTIVITIES
Proceeds from the sale/maturity of marketable securities	13,553	8,333
Purchases of marketable securities	(9,749)	(5,279)
Purchases of property and equipment	(53)	(41)
Proceeds from sale of property and equipment	20
Net cash provided by investing activities	3,771	3,013
FINANCING ACTIVITIES
Proceeds from issuance of convertible promissory notes, net of issuance costs	7,338
Principal payments on notes payable	(1,800)
Proceeds from issuance of common stock	41	3
Cash paid for deferred debt and equity issuance costs	(338)	(296)
Net cash provided by (used in) financing activities	5,241	(293)
Net increase (decrease) in cash and cash equivalents	1,445	(3,347)
Cash and cash equivalents, beginning of period	5,510	8,150
Cash and cash equivalents, end of period	6,955	4,803
NONCASH FINANCING AND INVESTING ACTIVITIES
Deferred debt and equity issuance costs in accounts payable and accrued liabilities	1,013	258
Property and equipment purchases included in accounts payable and accrued liabilities	$ 27	$ 109

Organization and Basis of Prese

Organization and Basis of Presentation	3 Months Ended
	Mar. 31, 2017
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Organization and Basis of Presentation	1. Organization and Basis of Presentation Tocagen Inc. (Tocagen or the Company) is a clinical-stage, cancer-selective gene therapy company focused on developing first-in-class, broadly-applicable product candidates designed to activate a patient’s immune system against their own cancer from within. The Company’s cancer-selective gene therapy platform is built on retroviral replicating vectors which are designed to selectively deliver therapeutic genes into the DNA of cancer cells. Tocagen’s gene therapy approach is designed to fight cancer through immunotherapeutic mechanisms of action without the autoimmune toxicities commonly experienced with other immunotherapies. From inception through March 31, 2017, the Company has devoted substantially all of its efforts to developing its gene therapy platform and its lead product candidate, Toca 511 & Toca FC, as well as raising capital and building its infrastructure. The Company has not generated revenues from its principal operations. Liquidity The Company has a limited operating history and the sales and income potential of the Company’s business and patient markets are unproven. The Company has experienced net losses and negative cash flows from operating activities since its inception. As of March 31, 2017, the Company had an accumulated deficit of $137.1 million and working capital of $14.0 million available to fund future operations. As the Company continues to incur net losses, its transition to profitability is dependent upon the successful development, approval, and commercialization of its product candidates and achieving a level of revenues adequate to support the Company’s cost structure. The Company may never achieve profitability, and unless and until it does, the Company will continue to need to raise additional capital. In performing the first step of the assessment under Accounting Standards Codification Topic 205-40, Presentation of Financial Statements - Going Concern, the Company concluded that, based on its cash resources available and the $86.9 million in estimated net proceeds obtained from its initial public offering (IPO), effective April 19, 2017, it will have sufficient resources to fund its business for at least the next 12 months from the date of this filing. Use of Estimates The Company’s financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP), which requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and expenses and related disclosures during the reporting period. Significant estimates in the Company’s financial statements relate to clinical trial accruals, the valuation of equity awards, and the development period used for license revenue recognition. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results may differ from these estimates under different assumptions or conditions. Interim Financial Reporting The accompanying unaudited condensed financial statements have been prepared pursuant to the rules and regulations of the Securities and Exchange Commission (SEC). Certain information and note disclosures normally included in annual audited financial statements prepared in accordance with GAAP have been omitted. The accompanying unaudited condensed financial statements include all known adjustments necessary for a fair presentation of the results of interim periods as required by GAAP. These adjustments consist primarily of normal recurring accruals and estimates that impact the carrying value of assets and liabilities. Actual results may materially differ from these estimates. Operating results for the three months ended March 31, 2017 are not necessarily indicative of the results that may be expected for the year ending December 31, 2017. The accompanying unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2016, which are included in the Company’s Registration Statement on Form S-1, as amended, originally filed with the SEC on March 9, 2017. Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision maker, or decision making group, in making decisions on how to allocate resources and assess performance. The Company views its operations and manages its business in one operating segment. No product revenue has been generated since inception and all assets are held in the United States.

Summary of Significant Accounti

Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Cash, Cash Equivalents and Marketable Securities Cash consists of the balance in a readily available checking account. Cash equivalents consist of money market funds, certificates of deposit and U.S. Treasury securities with remaining maturities of three months or less at the time of purchase, and are considered highly liquid investments. Marketable securities consist of certificates of deposit and U.S. Treasury securities that have original maturities greater than three months at the time of purchase. The Company classifies its investments as available-for-sale and records such assets at fair value in the balance sheet, with unrealized gains and losses, if any, reported in stockholders’ deficit. Realized gains and losses are calculated on the specific identification method and recorded to interest income. A decline in the market value of any marketable security below cost that is determined to be other-than-temporary results in a revaluation of its carrying amount to fair value and a new cost basis for the security. Impairment losses are recognized in other expense in the statement of operations. Concentration of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash equivalents and marketable securities. The Company’s investment policy includes guidelines for the quality of the related institutions and financial instruments, and defines allowable investments that the Company may invest in, which the Company believes minimizes the exposure to concentration of credit risk. The Company has no financial instruments with off-balance sheet risk of loss. Deferred Equity Issuance Costs Specific incremental costs directly attributable to a proposed or actual offering of securities are deferred and charged against the gross proceeds of the offering through additional paid-in capital. Fair Value of Financial Instruments The Company’s financial instruments consist principally of cash, cash equivalents, marketable securities, accounts payable, notes payable, convertible promissory notes payable and preferred stock warrant liabilities. The authoritative accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the authoritative accounting guidance establishes a three-tier fair value hierarchy that prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, 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; and Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Clinical Trial Accruals Expenses related to clinical studies are based on estimates of the services received and efforts expended pursuant to the Company’s contract arrangements. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to the Company’s service providers will temporarily exceed the level of services provided and result in a prepayment of the clinical expense. Payments under some of these contracts depend on factors such as the successful enrollment of patients, site initiation and the completion of clinical milestones. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from its estimate, the Company adjusts the accrual or prepaid expense balance accordingly. Revenue Recognition Revenue is comprised of license revenue from the up-front payment that the Company received under its license and collaboration arrangement with Siemens Healthcare Diagnostics Inc Revenue is recognized for each unit of accounting when all of the following criteria are met: • Persuasive evidence of an arrangement exists • Delivery of the Company’s obligations under the arrangement has occurred • The seller’s price to the buyer is fixed or determinable • Collectability is reasonably assured Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as long-term deferred revenue. The Company analyzes multiple-element arrangements based on the relevant authoritative guidance. Pursuant to the guidance, the Company evaluates multiple-element arrangements to determine (1) the deliverables included in the arrangement and (2) whether the individual deliverables represent separate units of accounting, or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires the Company to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer (a collaboration partner to date) on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in its control. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. The Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (VSOE) of selling price, if available, third-party evidence (TPE) of selling price if VSOE is not available, or best estimate of selling price (BESP) if neither VSOE nor TPE is available. The Company uses BESP to estimate the selling price, since it generally does not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the collaboration partner and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company then applies the applicable revenue recognition criteria to each of the separate units of accounting in determining the appropriate period and pattern of recognition. If there is no discernible pattern of performance and/or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight-line basis over the period it expects to complete its performance obligations. Research and Development Costs Research and development expenses consist primarily of salaries and benefits, clinical trial costs, costs related to acquiring and manufacturing clinical trial materials, contract services, facilities costs, overhead costs, and depreciation. All research and development costs are expensed as incurred. Debt Issuance Costs Debt issuance costs incurred to obtain debt financing are deferred and are amortized over the term of the debt using the effective interest method. The costs are recorded as a reduction to the carrying value of the debt and the amortization expense is included in interest expense in the statement of operations. Warrants for Shares of Preferred Stock The Company accounts for warrants for shares of preferred stock with conversion features as liabilities in the accompanying balance sheets at their fair value on the date of issuance. The warrant liabilities are revalued at each balance sheet date until such instruments are exercised or expire, with changes in the fair value between reporting periods recorded as other income or expense in the statement of operations. Comprehensive Income (Loss) All components of comprehensive income (loss) are reported in the financial statements in the period in which they are recognized. Other comprehensive income (loss) is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on investments. The Company’s only component of other comprehensive loss is unrealized gains (losses) on investments. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented. Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of stock options granted to employees. For awards with time-based vesting provisions, the Company estimates the fair value of stock options on the date of grant using the Black-Scholes option pricing model and recognizes the expense over the requisite service period of the awards, which is generally the vesting period, on a straight-line basis. For awards with performance-based vesting provisions, the Company estimates the fair value of stock option grants on the date of grant, or the date when all of the terms of the grant have been agreed to, if later, and recognizes the expense based on the probability of the occurrence of the individual milestones at each reporting period. The expense is recognized over the implicit service period that commences once management believes the performance criteria are probable of being met. The Company accounts for forfeitures when they occur, and reverses any compensation cost previously recognized for awards for which the requisite service has not been completed, in the period that the award is forfeited. The Company accounts for stock options and stock warrants granted to non-employees using the fair value approach. These option and warrant grants are subject to periodic revaluation over their vesting terms. Net Loss Per Share Basic and diluted net loss per common share for the periods presented is computed by dividing net loss by the weighted-average number of common shares outstanding during the respective periods, without consideration of common stock equivalents as they are anti-dilutive. Common stock equivalents that could potentially dilute earnings in the future are comprised of shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes payable, shares issuable upon the conversion of convertible preferred stock, options to purchase shares of common stock outstanding under the Company’s equity incentive plan and warrants for the purchase of shares of common and preferred stock. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Common stock equivalents from potentially dilutive securities, excluding shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes, that are not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows: Three Months Ended March 31, 2017 2016 Convertible preferred stock (as-converted) 6,690,066 6,690,066 Common stock options 1,464,177 722,072 Common stock warrant 724 724 Convertible preferred stock warrants (as-converted) 9,936 9,936 Total 8,164,903 7,422,798 Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued new revenue recognition guidance which outlines a single comprehensive revenue model for entities to use in accounting for revenue arising from contracts with customers. The guidance supersedes most current revenue recognition guidance, including industry-specific guidance. The guidance provides that an entity recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The guidance will be effective on January 1, 2018 and earlier application is permitted only for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. The guidance allows for either a full retrospective adoption, in which the standard is applied to all of the periods presented, or a modified retrospective adoption, in which the standard is applied to the most current period presented in the financial statements. As of March 31, 2017, revenue has been generated exclusively from the Company’s license and collaboration arrangement with Siemens. The Company is currently evaluating the potential impact that this guidance may have on its financial position and results of operations as it relates to this single arrangement, and expects to elect the modified retrospective adoption method. In January 2016, the FASB issued new guidance that amends certain aspects of the recognition, measurement, presentation and disclosure of financial instruments. The amendments include the elimination of the available-for-sale classification of equity investments and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income (loss). The new guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and requires a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. Early adoption is not permitted. The Company’s marketable securities are currently accounted for as available-for-sale financial instruments with changes in fair value recognized in other comprehensive income (loss). At the time of adoption, any amounts in accumulated other comprehensive income (loss) related to such financial instruments would be reclassified to non-operating income (expense) in the statement of operations. As of March 31, 2017, a net unrealized loss of $1,000 related to these investments was recorded in accumulated other comprehensive loss in the accompanying balance sheet. In February 2016, the FASB issued new accounting guidance that amends the existing accounting standards for leases. Under the new guidance, lessees will be required to recognize for all leases, with the exception of short-term leases, a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact of adopting this guidance.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	3. Fair Value of Financial Instruments Fair Values of Assets and Liabilities Measured on a Recurring Basis The following tables summarize the Company’s assets and liabilities that require fair value measurements on a recurring basis and their respective input levels based on the fair value hierarchy (in thousands): Fair Value Measurements at End of Period Using: Total Quoted Prices for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) March 31, 2017 Cash equivalents: U.S. Treasury securities $ 1,869 $ 1,869 $ — $ — Marketable securities: Certificates of deposit $ 11,480 $ — $ 11,480 $ — U.S. Treasury securities 10,450 10,450 — — $ 21,930 $ 10,450 $ 11,480 $ — Preferred stock warrant liabilities $ 67 $ — $ — $ 67 Fair Total Quoted Market Prices for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2016 Cash equivalents: Certificates of deposit $ 240 $ — $ 240 $ — Marketable securities: Certificates of deposit $ 22,777 $ — $ 22,777 $ — U.S. Treasury securities 2,958 2,958 — — $ 25,735 $ 2,958 $ 22,777 $ — Preferred stock warrant liabilities $ 126 $ — $ — $ 126 Marketable Securities . For fair values determined by Level 1 inputs, which utilize quoted prices in active markets for identical assets, the level of judgment required to estimate fair value is relatively low. The fair values of investments in U.S. treasury securities were determined using Level 1 inputs. Fair values determined by Level 2 inputs, which utilize data points that are observable such as quoted prices, interest rates and yield curves, require the exercise of judgment and use of estimates, that if changed, could significantly affect the Company’s financial position and results of operations. Investments in certificates of deposit are valued using Level 2 inputs. Level 2 securities are initially valued at the transaction price and subsequently valued and reported utilizing inputs other than quoted prices that are observable either directly or indirectly, such as quotes from third-party pricing vendors. There were no transfers in or out of Level 1 or Level 2 investments during the three months ended March 31, 2017 or 2016. At March 31, 2017 and December 31, 2016, the Company had investments in money market funds of $3.1 million and $2.2 million, respectively, that were measured at fair value using the net asset value per share (or its equivalent) that have not been classified in the fair value hierarchy. The funds invest primarily in U.S. government securities. Warrant Liabilities . The Company’s preferred stock warrants are accounted for as liabilities and measured at fair value on a recurring basis as they are convertible into preferred stock which is contingently redeemable under conditions that are not in the control of the Company. The Company estimates fair values of these warrant liabilities utilizing the Black-Scholes option pricing model, which requires Level 3 inputs. Estimating fair values of derivative financial instruments, including Level 3 instruments, requires the use of significant and subjective inputs that may, and are likely to, change over the duration of the instrument with related changes in internal and external market factors, including changes in the estimated fair value of the Company’s equity securities. A 10% increase in the fair value of preferred stock at March 31, 2017 would result in an aggregate increase in the estimated fair value of the preferred stock warrant liabilities of $8,000. The following table summarizes the activity in liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3 inputs) (in thousands): Preferred Stock Liabilities Balance at December 31, 2016 $ 126 Gain on warrant valuation included in other income (expense), net (59 ) Balance at March 31, 2017 $ 67 Fair Values of Other Financial Instruments The carrying amounts of certain of the Company’s financial instruments, including cash and accounts payable, approximate their respective fair values due to their short-term nature. The carrying amount of the Company’s notes payable of $15.8 million at March 31, 2017 approximated their fair value as the terms of the notes are consistent with the market terms of transactions with similar profiles of one of the lenders as of those dates (Level 3 inputs). The carrying amount of the Company’s convertible promissory notes payable of $11.0 million at March 31, 2017 approximated their fair value due to their recent issuance during the three months ended March 31, 2017 (Level 3 inputs).

Certain Financial Statement Cap

Certain Financial Statement Caption Information	3 Months Ended
	Mar. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Certain Financial Statement Caption Information	4. Certain Financial Statement Caption Information Marketable Securities The following is a summary of the Company’s marketable securities (in thousands): Maturity (in years) Amortized Cost Unrealized Gain Unrealized Loss Fair Value March 31, 2017: Certificates of deposit 1 or less $ 9,822 $ 1 $ (1 ) $ 9,822 Certificates of deposit >1 and <5 1,658 — — 1,658 U.S. Treasury securities 1 or less 10,451 1 (2 ) 10,450 $ 21,931 $ 2 $ (3 ) $ 21,930 December 31, 2016: Certificates of deposit 1 or less $ 19,299 $ 1 $ (2 ) $ 19,298 Certificates of deposit >1 and <5 3,478 1 — 3,479 U.S. Treasury securities 1 or less 1,678 — — 1,678 U.S. Treasury securities >1 and <5 1,280 4 (4 ) 1,280 $ 25,735 $ 6 $ (6 ) $ 25,735 The Company has classified all of its available-for-sale investment securities, including those with maturity greater than one year, as current assets on the balance sheet based on the highly liquid nature of these investment securities and because these investment securities are considered available for use in current operations. There were no impairments considered other-than-temporary during the periods presented, as it is management’s intention and ability to hold the securities until a recovery of the cost basis or recovery of fair value. Gross realized gains and losses on sales of marketable securities were immaterial for all periods presented. Accrued Liabilities Accrued liabilities are comprised of (in thousands): March 31, 2017 December 31, 2016 Clinical trial expenses $ 2,790 $ 2,114 Contract manufacturing services 1,564 1,508 Payroll and other employee-related expenses 1,591 728 Professional fees 1,084 459 Contract research services 91 114 Interest payable 111 120 Other 625 394 Total accrued liabilities $ 7,856 $ 5,437

Notes Payable

Notes Payable	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Notes Payable	5. Notes Payable Loan Agreement On October 30, 2015, the Company entered into a Loan and Security Agreement (the Loan Agreement) with two lenders whereby it borrowed $18.0 million (the Loans) on October 30, 2015. Balances under the Loan Agreement bear a floating rate of interest equal to the greater of 7.75% or the monthly prime rate plus 4.50% (8.25% and 8.00% at March 31, 2017 and December 31, 2016, respectively), and are due in monthly principal and interest payments, with final maturity of the Loans in May 2019. Each Loan bears a final payment fee of 7.95% of the original principal amount due upon maturity. The costs incurred to issue the Loans of $0.6 million were deferred and are included in the discount to the carrying value of the Loans in the accompanying balance sheets. The Loans also include a final payment fee of $1.4 million due at the earlier of prepayment or the maturity date of the Loans. The deferred costs and the final payment fee are amortized to interest expense over the expected term of the Loans using the effective interest method. The effective interest rates on the Loans at March 31, 2017 and December 31, 2016 are 11.44% and 11.19%, respectively. The aggregate carrying amounts of the Loans are comprised of the following (in thousands): March 31, 2017 December 31, 2016 Principal $ 15,600 $ 17,400 Add: accreted liability for final payment fee 561 462 Less: unamortized discount (378 ) (421 ) $ 15,783 $ 17,441 The Loans are secured by substantially all of the Company’s assets other than its intellectual property, except rights to payment from the sale, licensing or disposition of such intellectual property. The Company is also required to maintain its primary operating accounts at all times with one of the lenders. The Loan Agreement contains customary conditions of borrowing, events of default and covenants, including covenants that restrict the Company’s ability to dispose of assets, merge with or acquire other entities, incur indebtedness and make distributions to holders of its capital stock. Should an event of default occur, including the occurrence of a material adverse change, the Company could be liable for immediate repayment of all obligations under the Loan Agreement. The Company does not believe it is likely that a material adverse change will occur. At March 31, 2017, the Company was in compliance with the covenants contained in the Loan Agreement. Future maturities of the Loans, including the final payment fee, as of March 31, 2017 are as follows (in thousands): March 31, 2017 Remainder of 2017 $ 5,400 Year ending December 31, 2018 7,200 Year ending December 31, 2019 4,431 17,031 Unaccreted balance for final payment fee on Loans (870 ) Unamortized discounts (378 ) 15,783 Less current portion (7,200 ) Noncurrent portion $ 8,583 Convertible Promissory Notes Payable and Subscription Liability During the three months ended March 31, 2017 and December 31, 2016, the Company issued convertible promissory notes payable to investors in aggregate principal amount of $7.5 million and $3.4 million, respectively, for a total aggregate principal amount of $10.9 million (the Convertible Notes). Of the Convertible Notes issued during the three months ended March 31, 2017, $140,000 was subscribed for at December 31, 2016, $250,000 was issued to a member of the Company’s board of directors and $10,000 was issued to the Company’s chief executive officer. The Convertible Notes, which bear interest at 7% per annum, are unsecured and are subordinated to the Loans. Principal and interest are due on November 21, 2018, unless the Company elects to extend the maturity date of the Convertible Notes to a date on or before November 21, 2019. At March 31, 2017 and December 31, 2016, the aggregate carrying amounts of the Convertible Notes are $11.0 million and $3.4 million, respectively, which are net of unamortized discounts of $36,000 and $34,000, respectively. At March 31, 2017 and December 31, 2016, the Convertible Notes include $1.3 million and $1.0 million, respectively, issued to members of the Company’s board of directors, and $35,000 and $25,000, respectively, issued to the Company’s chief executive officer. The effective interest rates on the Convertible Notes at March 31, 2017 and December 31, 2016 are 7.20% and 7.54%, respectively. The Convertible Notes provide for mandatory share-settlement of all outstanding principal plus accrued and unpaid interest as follows: (1) upon a qualifying financing event whereby the Company issues shares of its preferred stock to investors, the Convertible Notes automatically convert into shares of the same class of preferred stock at an amount equal to the price per share at which the preferred stock was issued to the investors; (2) upon the closing of a qualified IPO, the Convertible Notes automatically convert into shares of common stock at an amount equal to the per share purchase price paid by the public in the IPO; (3) immediately prior to the closing of a qualifying change of control transaction, the Convertible Notes automatically convert into shares of the latest-issue preferred stock determined by dividing (i) the sum of (x) 110% of the outstanding principal plus (y) accrued and unpaid interest by (ii) the last price paid by the investors of such series of preferred stock; or (4) upon the maturity date, the Convertible Notes automatically convert into shares of the latest-issue preferred stock determined by dividing the outstanding principal and interest by the last price paid by investors for the purchase of such series of preferred stock. Subsequent to March 31, 2017, on April 19, 2017, upon completion of the Company’s IPO, $11.1 million of aggregate principal and accrued interest underlying the Convertible Notes were automatically converted into an aggregate of 1,109,176 shares of the Company’s common stock at the IPO price of $10.00 per share.

Common Stock, Convertible Prefe

Common Stock, Convertible Preferred Stock and Stockholders’ Deficit	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Common Stock, Convertible Preferred Stock and Stockholders Deficit	6. Common Stock, Convertible Preferred Stock and Stockholders’ Deficit In March 2017, the Company’s board of directors and stockholders approved a 1-for-6.9 reverse stock split of its outstanding common stock. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented. Changes in the number of shares of the Company’s convertible preferred and common stock outstanding and total stockholders’ deficit during the three months ended March 31, 2017 were as follows (in thousands, except share amounts): Shares of Convertible Preferred Stock Shares of Common Stock Total Stockholders’ Deficit Balance, December 31, 2016 46,163,605 2,202,517 $ (124,417 ) Stock-based compensation — — 529 Exercise of stock options — 24,648 41 Fractional shares adjustment upon reverse stock split — 2 — Other comprehensive loss — — (1 ) Net loss — — (9,073 ) Balance, March 31, 2017 46,163,605 2,227,167 $ (132,921 ) Convertible Preferred Stock The authorized, issued and outstanding shares, and liquidation preferences of convertible preferred stock by series as of March 31, 2017 and December 31, 2016 are as follows (in thousands, except share amounts): Shares Authorized Shares Issued and Outstanding Liquidation Preference Series A 6,700,000 6,700,000 $ 6,700 Series B 8,676,800 8,676,800 10,846 Series C 5,697,601 5,697,601 9,116 Series C-1 1,578,948 1,578,948 3,000 Series D 3,888,375 3,888,375 7,777 Series E 2,485,250 2,485,250 9,941 Series F 5,904,501 5,904,501 25,980 Series G 2,432,068 2,432,068 12,160 Series H 12,000,000 8,800,062 46,200 Undesignated 1,636,457 — — 51,000,000 46,163,605 $ 131,720 The Company records each series of convertible preferred stock based upon gross proceeds on the respective dates of issuance, net of issuance costs. A right to receive payment will only occur upon the liquidation or winding up of the Company, a greater than 50% change of control or sale of substantially all of the assets of the Company. As this right to receive payment is considered a deemed liquidation outside the control of the Company, all shares of convertible preferred stock have been presented outside of permanent equity in accordance with accounting guidance for redeemable securities. Further, the Company is not adjusting the carrying values of the convertible preferred stock as it is uncertain whether or when a redemption event will occur. Adjustments to increase the carrying values will be made if it becomes probable that such redemption will occur. Dividends The holders of the convertible preferred stock are entitled to receive, in preference to the holders of common stock, noncumulative dividends at a rate of 5% per annum, when, as and if declared by the Company’s board of directors. As of March 31, 2017, the Company’s board of directors has not declared any dividends. Liquidation Preferences The holders of the convertible preferred stock are entitled to receive a liquidation payment, before any distribution or payment to the holders of common stock, pari passu on a pro rata basis per share until the holders have received an amount equal to the applicable original purchase price per share of convertible preferred stock. Conversion The convertible preferred stock is convertible into common stock on a 1-for-6.9 basis at any time, subject to customary anti-dilution adjustments, and automatically converts into common stock upon the consent of a majority of the holders of outstanding convertible preferred stock or, for any series of convertible preferred stock, a majority of the holders of such series, or upon a public offering with aggregate proceeds to the Company of at least $10 million. The convertible preferred stock also includes anti-dilution provisions making it subject to adjustment for stock splits, stock dividends, recapitalizations and similar events. Shares of the Series G and H convertible preferred stock are also subject to transfer restrictions until the earlier of a registration under the Securities Act of 1933, as amended (Securities Act), covering the proposed disposition, the closing date of the Company’s first firm commitment underwritten public offering of its common stock registered under the Securities Act, and the closing date of an acquisition or asset transfer. Subsequent to March 31, 2017, on April 19, 2017, upon completion of the Company’s IPO, all of the Company’s outstanding shares of convertible preferred stock were converted into an aggregate of 6,690,066 shares of the Company’s common stock. Voting All series of the Company’s convertible preferred stock vote together with the common stock on an as-converted basis. Common Stock The Company had 2,227,167 and 2,202,517 shares of common stock outstanding as of March 31, 2017 and December 31, 2016, respectively. Common Stock Reserved for Future Issuance Common stock reserved for future issuance at March 31, 2017 is as follows and excludes shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes payable: Issued and Outstanding: Convertible preferred stock (as-converted) 6,690,066 Stock options 1,464,177 Warrants for common stock 724 Warrants for preferred stock (as-converted) 9,936 Shares reserved for future award grants 69,525 Total 8,234,428

Equity Incentive Plan and Stock

Equity Incentive Plan and Stock-Based Compensation	3 Months Ended
	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Equity Incentive Plan and Stock-Based Compensation	7. Equity Incentive Plan and Stock-Based Compensation 2009 Equity Incentive Plan The Company’s 2009 Equity Incentive Plan, as amended (the 2009 Plan), provides for the issuance of stock options, restricted stock awards and other equity based awards to employees, directors and consultants of the Company. As of March 31, 2017, awards for up to 1,533,702 shares of common stock are reserved under the 2009 Plan, of which 1,464,177 shares are reserved for issuance upon exercise of granted and outstanding stock options and 69,525 shares are available for future grants. All grants of common stock options under the 2009 Plan expire in 10 years. Grants with time-based vesting provisions are subject to a four-year vesting schedule with 25% vesting after the first year, and the balance vesting monthly over the remaining 36 months. Grants with performance-based vesting provisions vest upon the achievement of three separate development and regulatory milestones, with one-third of the options vesting upon the achievement of each milestone. The following table summarizes stock option activity under the 2009 Plan: Shares Subject to Options Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic (in thousands) Outstanding at December 31, 2016 1,385,855 $ 11.35 Granted 103,934 $ 15.12 Exercised (24,648 ) $ 1.64 Forfeitures and cancellations (964 ) $ 12.11 Outstanding at March 31, 2017 1,464,177 $ 11.78 8.0 $ 3,223 Time-based options at March 31, 2017: Outstanding 1,275,526 $ 11.11 7.7 $ 3,223 Vested and expected to vest 1,275,526 $ 11.11 7.7 $ 3,223 Exercisable 574,746 $ 5.97 5.8 $ 3,221 Performance-based options at March 31, 2017: Outstanding 188,651 $ 16.30 9.7 $ — Vested and expected to vest — $ — — $ — Exercisable — $ — — $ — The total fair value of options vested during the three months ended March 31, 2017 and 2016, was $1.0 million and $0.2 million, respectively. The aggregate intrinsic value of options is calculated as the difference between the exercise price of the options and the fair value of the Company’s common stock for those options that had exercise prices lower than the fair value of the Company’s common stock. The aggregate intrinsic value of stock options exercised during the three months ended March 31, 2017 and 2016, was $0.3 million and $9,000, respectively. Stock-Based Compensation Expense The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Three Months Ended March 31, 2017 Time-Based Vesting Provisions Performance-Based Vesting Provisions Risk-free interest rate 2.17 % 1.98%-2.17% Expected volatility 76.0 % 75.2%-76.3% Weighted-average volatility 76.0 % 75.9 % Dividend yield 0 % 0 % Weighted-average expected term (in years) 6.1 6.3 Weighted-average grant date fair value per share $ 6.79 $ 6.73 Risk-free interest rate . The Company bases the risk-free interest rate assumption on U.S. Treasury constant maturities with maturities similar to those of the expected term of the award being valued. Expected volatility . Due to the Company’s lack of company-specific historical or implied volatility data, the Company has based its estimate of expected volatility on the historical volatility of a group of similar companies in the life sciences industry whose shares are publicly traded. The Company selects the peer group based on comparable characteristics, including development stage, product pipeline, and enterprise value. The Company computes historical volatility data using the daily closing prices for the selected companies’ shares during the equivalent period of the calculated expected term of the stock-based awards. The Company will continue to apply this process until sufficient amount of historical information regarding the volatility of its own stock price become available. Expected term . The expected term of employee stock options granted with time-based vesting provisions was calculated using the simplified method which utilizes the midpoint between the weighted average time of vesting and the end of the contractual term. The expected term of employee stock options granted with performance-based vesting provisions was calculated using the midpoint between the estimated service period and the contractual term of the option. These methods were utilized due to a lack of historical exercise behavior by the Company's employees. Expected dividend yield . The Company bases the expected dividend yield assumption on the fact that it has never paid, and does not expect to pay, dividends in the foreseeable future. The Company calculates the estimated fair value of each non-employee stock option award at the date of grant using Black-Scholes option pricing model with the assumptions generally consistent with those used for employee stock options, with the exception of expected term, which is over the contractual life. The Company has not recognized non-cash stock-based compensation expense for outstanding options to purchase 188,651 shares of common stock with performance-based vesting provisions after its evaluation that the occurrence of the individual milestones is not probable as of March 31, 2017. Total non-cash stock-based compensation expense for all stock awards, net of forfeitures recognized as they occur, that was recognized in the statements of operations is as follows (in thousands): Three Months Ended March 31, 2017 2016 Research and development $ 142 $ 109 General and administrative 387 156 Total $ 529 $ 265 Unrecognized compensation expense at March 31, 2017 was $7.4 million which is expected to be recognized over a weighted-average period of 3.0 years.

Subsequent Events

Subsequent Events	3 Months Ended
	Mar. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	8. Subsequent Events Initial Public Offering On April 19, 2017, the Company completed its IPO, whereby the Company sold an aggregate of 9,775,000 shares of its common stock, at $10.00 per share, resulting in estimated net proceeds of $86.9 million after underwriting discounts, commissions and estimated offering costs of $10.9 million, of which $0.3 million of the costs were paid during the three months ended March 31, 2017. In addition, in connection with the IPO, all of the Company’s outstanding shares of convertible preferred stock were converted into an aggregate of 6,690,066 shares of the Company’s common stock, warrants to purchase shares of the Company’s Series H Preferred Stock were converted into warrants to purchase 9,936 shares of the Company’s common stock, each at an exercise price of $36.23 per share, and $11.1 million of aggregate principal and accrued interest underlying the Convertible Notes were automatically converted into an aggregate of 1,109,176 shares of the Company’s common stock at the IPO price of $10.00 per share. Upon completion of the IPO, the Company’s authorized capital stock consists of 200,000,000 shares of common stock, par value $0.001 per share, and 10,000,000 shares of preferred stock, par value $0.001 per share. 2017 Equity Incentive Plan In March 2017, the Company’s board of directors and stockholders approved and adopted the Company’s 2017 Equity Incentive Plan (the 2017 Plan), which became effective on April 12, 2017. The 2017 Plan provides for the grant of incentive stock options (ISOs), nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance based stock awards, other forms of equity compensation and performance cash awards. ISOs may be granted only to employees. All other awards may be granted to employees, including officers, and to the Company’s non-employee directors and consultants, and affiliates. Initially, 1,600,000 new shares of common stock were approved for issuance under the 2017 Plan and, on April 12, 2017, 75,517 shares of common stock reserved for issuance under the 2009 Plan were added to the shares initially reserved under the 2017 Plan. No further grants will be made under the 2009 Plan and any shares subject to outstanding stock options under the 2009 Plan that would otherwise be returned to the 2009 Plan will instead be added to the shares initially reserved under the 2017 Plan. In addition, the number of shares of common stock reserved for issuance under the 2017 Plan will automatically increase on January 1 of each year, beginning on January 1, 2018 and continuing through and including January 1, 2027, by 4% of the total number of shares of the Company’s capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company’s board of directors. 2017 Employee Stock Purchase Plan In March 2017, the Company’s board of directors and stockholders approved and adopted the 2017 Employee Stock Purchase Plan (the ESPP), which became effective on April 12, 2017. The ESPP authorizes the issuance of 250,000 shares of the Company’s common stock pursuant to purchase rights granted to our employees or to employees of any of the Company’s designated affiliates. The number of shares of common stock reserved for issuance will automatically increase on January 1 of each calendar year, from January 1, 2018 through January 1, 2027 by the lesser of (a) 1% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year, (b) 300,000 shares, or (c) a number determined by the Company’s board of directors that is less than (a) and (b).

Summary of Significant Accoun15

Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Use of Estimates	Use of Estimates The Company’s financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP), which requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements, and expenses and related disclosures during the reporting period. Significant estimates in the Company’s financial statements relate to clinical trial accruals, the valuation of equity awards, and the development period used for license revenue recognition. Estimates are periodically reviewed in light of changes in circumstances, facts and experience. Actual results may differ from these estimates under different assumptions or conditions.
Cash, Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities Cash consists of the balance in a readily available checking account. Cash equivalents consist of money market funds, certificates of deposit and U.S. Treasury securities with remaining maturities of three months or less at the time of purchase, and are considered highly liquid investments. Marketable securities consist of certificates of deposit and U.S. Treasury securities that have original maturities greater than three months at the time of purchase. The Company classifies its investments as available-for-sale and records such assets at fair value in the balance sheet, with unrealized gains and losses, if any, reported in stockholders’ deficit. Realized gains and losses are calculated on the specific identification method and recorded to interest income. A decline in the market value of any marketable security below cost that is determined to be other-than-temporary results in a revaluation of its carrying amount to fair value and a new cost basis for the security. Impairment losses are recognized in other expense in the statement of operations.
Concentration of Credit Risk and Off-Balance Sheet Risk	Concentration of Credit Risk and Off-Balance Sheet Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash equivalents and marketable securities. The Company’s investment policy includes guidelines for the quality of the related institutions and financial instruments, and defines allowable investments that the Company may invest in, which the Company believes minimizes the exposure to concentration of credit risk. The Company has no financial instruments with off-balance sheet risk of loss.
Deferred Equity Issuance Costs	Deferred Equity Issuance Costs Specific incremental costs directly attributable to a proposed or actual offering of securities are deferred and charged against the gross proceeds of the offering through additional paid-in capital.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company’s financial instruments consist principally of cash, cash equivalents, marketable securities, accounts payable, notes payable, convertible promissory notes payable and preferred stock warrant liabilities. The authoritative accounting guidance defines fair value, establishes a consistent framework for measuring fair value and expands disclosure for each major asset and liability category measured at fair value on either a recurring or nonrecurring basis. Fair value is defined as an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, the authoritative accounting guidance establishes a three-tier fair value hierarchy that prioritizes the inputs used in measuring fair value as follows: Level 1: Observable inputs such as quoted prices in active markets; Level 2: Inputs, other than the quoted prices in active markets, 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; and Level 3: Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities.
Clinical Trial Accruals	Clinical Trial Accruals Expenses related to clinical studies are based on estimates of the services received and efforts expended pursuant to the Company’s contract arrangements. The financial terms of these agreements are subject to negotiation, vary from contract to contract and may result in uneven payment flows. There may be instances in which payments made to the Company’s service providers will temporarily exceed the level of services provided and result in a prepayment of the clinical expense. Payments under some of these contracts depend on factors such as the successful enrollment of patients, site initiation and the completion of clinical milestones. The Company makes estimates of its accrued expenses as of each balance sheet date in its financial statements based on facts and circumstances known at that time. In accruing service fees, the Company estimates the time period over which services will be performed and the level of effort to be expended in each period. If the actual timing of the performance of services or the level of effort varies from its estimate, the Company adjusts the accrual or prepaid expense balance accordingly.
Revenue Recognition	Revenue Recognition Revenue is comprised of license revenue from the up-front payment that the Company received under its license and collaboration arrangement with Siemens Healthcare Diagnostics Inc Revenue is recognized for each unit of accounting when all of the following criteria are met: • Persuasive evidence of an arrangement exists • Delivery of the Company’s obligations under the arrangement has occurred • The seller’s price to the buyer is fixed or determinable • Collectability is reasonably assured Amounts received prior to satisfying the revenue recognition criteria are recorded as deferred revenue in the Company’s balance sheets. Amounts expected to be recognized as revenue within the 12 months following the balance sheet date are classified as deferred revenue. Amounts not expected to be recognized as revenue within the 12 months following the balance sheet date are classified as long-term deferred revenue. The Company analyzes multiple-element arrangements based on the relevant authoritative guidance. Pursuant to the guidance, the Company evaluates multiple-element arrangements to determine (1) the deliverables included in the arrangement and (2) whether the individual deliverables represent separate units of accounting, or whether they must be accounted for as a combined unit of accounting. This evaluation involves subjective determinations and requires the Company to make judgments about the individual deliverables and whether such deliverables are separable from the other aspects of the contractual relationship. Deliverables are considered separate units of accounting provided that: (i) the delivered item(s) has value to the customer (a collaboration partner to date) on a standalone basis and (ii) if the arrangement includes a general right of return relative to the delivered item(s), delivery or performance of the undelivered item(s) is considered probable and substantially in its control. In assessing whether an item has standalone value, the Company considers factors such as the research, manufacturing and commercialization capabilities of the collaboration partner and the availability of the associated expertise in the general marketplace. In addition, the Company considers whether the collaboration partner can use the other deliverable(s) for their intended purpose without the receipt of the remaining element(s), whether the value of the deliverable is dependent on the undelivered item(s) and whether there are other vendors that can provide the undelivered element(s). Arrangement consideration that is fixed or determinable is allocated among the separate units of accounting using the relative selling price method. The Company determines the estimated selling price for units of accounting within each arrangement using vendor-specific objective evidence (VSOE) of selling price, if available, third-party evidence (TPE) of selling price if VSOE is not available, or best estimate of selling price (BESP) if neither VSOE nor TPE is available. The Company uses BESP to estimate the selling price, since it generally does not have VSOE or TPE of selling price for its units of accounting. Determining the BESP for a unit of accounting requires significant judgment. In developing the BESP for a unit of accounting, the Company considers applicable market conditions and relevant entity-specific factors, including factors that were contemplated in negotiating the agreement with the collaboration partner and estimated costs. The Company validates the BESP for units of accounting by evaluating whether changes in the key assumptions used to determine the BESP will have a significant effect on the allocation of arrangement consideration between multiple units of accounting. The Company then applies the applicable revenue recognition criteria to each of the separate units of accounting in determining the appropriate period and pattern of recognition. If there is no discernible pattern of performance and/or objectively measurable performance measures do not exist, then the Company recognizes revenue under the arrangement on a straight-line basis over the period it expects to complete its performance obligations.
Research and Development Costs	Research and Development Costs Research and development expenses consist primarily of salaries and benefits, clinical trial costs, costs related to acquiring and manufacturing clinical trial materials, contract services, facilities costs, overhead costs, and depreciation. All research and development costs are expensed as incurred.
Debt Issuance Costs	Debt Issuance Costs Debt issuance costs incurred to obtain debt financing are deferred and are amortized over the term of the debt using the effective interest method. The costs are recorded as a reduction to the carrying value of the debt and the amortization expense is included in interest expense in the statement of operations.
Warrants for Shares of Preferred Stock	Warrants for Shares of Preferred Stock The Company accounts for warrants for shares of preferred stock with conversion features as liabilities in the accompanying balance sheets at their fair value on the date of issuance. The warrant liabilities are revalued at each balance sheet date until such instruments are exercised or expire, with changes in the fair value between reporting periods recorded as other income or expense in the statement of operations.
Comprehensive Income (Loss)	Comprehensive Income (Loss) All components of comprehensive income (loss) are reported in the financial statements in the period in which they are recognized. Other comprehensive income (loss) is defined as the change in equity during a period from transactions and other events and circumstances from non-owner sources, including unrealized gains and losses on investments. The Company’s only component of other comprehensive loss is unrealized gains (losses) on investments. Comprehensive gains (losses) have been reflected in the statements of operations and comprehensive loss for all periods presented.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the cost of the grant date fair value of stock options granted to employees. For awards with time-based vesting provisions, the Company estimates the fair value of stock options on the date of grant using the Black-Scholes option pricing model and recognizes the expense over the requisite service period of the awards, which is generally the vesting period, on a straight-line basis. For awards with performance-based vesting provisions, the Company estimates the fair value of stock option grants on the date of grant, or the date when all of the terms of the grant have been agreed to, if later, and recognizes the expense based on the probability of the occurrence of the individual milestones at each reporting period. The expense is recognized over the implicit service period that commences once management believes the performance criteria are probable of being met. The Company accounts for forfeitures when they occur, and reverses any compensation cost previously recognized for awards for which the requisite service has not been completed, in the period that the award is forfeited. The Company accounts for stock options and stock warrants granted to non-employees using the fair value approach. These option and warrant grants are subject to periodic revaluation over their vesting terms.
Net Loss Per Share	Net Loss Per Share Basic and diluted net loss per common share for the periods presented is computed by dividing net loss by the weighted-average number of common shares outstanding during the respective periods, without consideration of common stock equivalents as they are anti-dilutive. Common stock equivalents that could potentially dilute earnings in the future are comprised of shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes payable, shares issuable upon the conversion of convertible preferred stock, options to purchase shares of common stock outstanding under the Company’s equity incentive plan and warrants for the purchase of shares of common and preferred stock. For all periods presented, there is no difference in the number of shares used to calculate basic and diluted shares outstanding due to the Company’s net loss position. Common stock equivalents from potentially dilutive securities, excluding shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes, that are not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows: Three Months Ended March 31, 2017 2016 Convertible preferred stock (as-converted) 6,690,066 6,690,066 Common stock options 1,464,177 722,072 Common stock warrant 724 724 Convertible preferred stock warrants (as-converted) 9,936 9,936 Total 8,164,903 7,422,798
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (FASB) issued new revenue recognition guidance which outlines a single comprehensive revenue model for entities to use in accounting for revenue arising from contracts with customers. The guidance supersedes most current revenue recognition guidance, including industry-specific guidance. The guidance provides that an entity recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. The guidance will be effective on January 1, 2018 and earlier application is permitted only for annual reporting periods beginning after December 15, 2016, including interim reporting periods within that reporting period. The guidance allows for either a full retrospective adoption, in which the standard is applied to all of the periods presented, or a modified retrospective adoption, in which the standard is applied to the most current period presented in the financial statements. As of March 31, 2017, revenue has been generated exclusively from the Company’s license and collaboration arrangement with Siemens. The Company is currently evaluating the potential impact that this guidance may have on its financial position and results of operations as it relates to this single arrangement, and expects to elect the modified retrospective adoption method. In January 2016, the FASB issued new guidance that amends certain aspects of the recognition, measurement, presentation and disclosure of financial instruments. The amendments include the elimination of the available-for-sale classification of equity investments and requires equity investments with readily determinable fair values to be measured at fair value with changes in fair value recognized in net income (loss). The new guidance is effective for fiscal years and interim periods within those years beginning after December 15, 2017, and requires a cumulative-effect adjustment to the balance sheet as of the beginning of the fiscal year of adoption. Early adoption is not permitted. The Company’s marketable securities are currently accounted for as available-for-sale financial instruments with changes in fair value recognized in other comprehensive income (loss). At the time of adoption, any amounts in accumulated other comprehensive income (loss) related to such financial instruments would be reclassified to non-operating income (expense) in the statement of operations. As of March 31, 2017, a net unrealized loss of $1,000 related to these investments was recorded in accumulated other comprehensive loss in the accompanying balance sheet. In February 2016, the FASB issued new accounting guidance that amends the existing accounting standards for leases. Under the new guidance, lessees will be required to recognize for all leases, with the exception of short-term leases, a lease liability, which is a lessee’s obligation to make lease payments arising from a lease, measured on a discounted basis and a right-of-use asset, which is an asset that represents the lessee’s right to use, or control the use of, a specified asset for the lease term. The new standard is effective for fiscal years beginning after December 15, 2018, including interim periods within those fiscal years. Early adoption is permitted. The Company is currently evaluating the impact of adopting this guidance.

Summary of Significant Accoun16

Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2017
Accounting Policies [Abstract]
Schedule of Common Stock Equivalents from Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share	Common stock equivalents from potentially dilutive securities, excluding shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes, that are not included in the calculation of diluted net loss per share, because to do so would be anti-dilutive, are as follows: Three Months Ended March 31, 2017 2016 Convertible preferred stock (as-converted) 6,690,066 6,690,066 Common stock options 1,464,177 722,072 Common stock warrant 724 724 Convertible preferred stock warrants (as-converted) 9,936 9,936 Total 8,164,903 7,422,798

Fair Value of Financial Instr17

Fair Value of Financial Instruments (Tables)	3 Months Ended
	Mar. 31, 2017
Fair Value Disclosures [Abstract]
Summary of Fair Values of Assets and Liabilities Measured on a Recurring Basis	The following tables summarize the Company’s assets and liabilities that require fair value measurements on a recurring basis and their respective input levels based on the fair value hierarchy (in thousands): Fair Value Measurements at End of Period Using: Total Quoted Prices for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) March 31, 2017 Cash equivalents: U.S. Treasury securities $ 1,869 $ 1,869 $ — $ — Marketable securities: Certificates of deposit $ 11,480 $ — $ 11,480 $ — U.S. Treasury securities 10,450 10,450 — — $ 21,930 $ 10,450 $ 11,480 $ — Preferred stock warrant liabilities $ 67 $ — $ — $ 67 Fair Total Quoted Market Prices for Identical Assets (Level 1) Significant Other Observable Inputs (Level 2) Significant Unobservable Inputs (Level 3) December 31, 2016 Cash equivalents: Certificates of deposit $ 240 $ — $ 240 $ — Marketable securities: Certificates of deposit $ 22,777 $ — $ 22,777 $ — U.S. Treasury securities 2,958 2,958 — — $ 25,735 $ 2,958 $ 22,777 $ — Preferred stock warrant liabilities $ 126 $ — $ — $ 126
Summary of Activity in Liabilities Measured at Fair Value on Recurring Basis	The following table summarizes the activity in liabilities measured at fair value on a recurring basis using significant unobservable inputs (Level 3 inputs) (in thousands): Preferred Stock Liabilities Balance at December 31, 2016 $ 126 Gain on warrant valuation included in other income (expense), net (59 ) Balance at March 31, 2017 $ 67

Certain Financial Statement C18

Certain Financial Statement Caption Information (Tables)	3 Months Ended
	Mar. 31, 2017
Balance Sheet Related Disclosures [Abstract]
Summary of Marketable Securities	The following is a summary of the Company’s marketable securities (in thousands): Maturity (in years) Amortized Cost Unrealized Gain Unrealized Loss Fair Value March 31, 2017: Certificates of deposit 1 or less $ 9,822 $ 1 $ (1 ) $ 9,822 Certificates of deposit >1 and <5 1,658 — — 1,658 U.S. Treasury securities 1 or less 10,451 1 (2 ) 10,450 $ 21,931 $ 2 $ (3 ) $ 21,930 December 31, 2016: Certificates of deposit 1 or less $ 19,299 $ 1 $ (2 ) $ 19,298 Certificates of deposit >1 and <5 3,478 1 — 3,479 U.S. Treasury securities 1 or less 1,678 — — 1,678 U.S. Treasury securities >1 and <5 1,280 4 (4 ) 1,280 $ 25,735 $ 6 $ (6 ) $ 25,735
Components of Accrued Liabilities	Accrued liabilities are comprised of (in thousands): March 31, 2017 December 31, 2016 Clinical trial expenses $ 2,790 $ 2,114 Contract manufacturing services 1,564 1,508 Payroll and other employee-related expenses 1,591 728 Professional fees 1,084 459 Contract research services 91 114 Interest payable 111 120 Other 625 394 Total accrued liabilities $ 7,856 $ 5,437

Notes Payable (Tables)

Notes Payable (Tables)	3 Months Ended
	Mar. 31, 2017
Debt Disclosure [Abstract]
Schedule of Aggregate Carrying Amounts of Loans	The aggregate carrying amounts of the Loans are comprised of the following (in thousands): March 31, 2017 December 31, 2016 Principal $ 15,600 $ 17,400 Add: accreted liability for final payment fee 561 462 Less: unamortized discount (378 ) (421 ) $ 15,783 $ 17,441
Schedule of Future Maturities Loans Including Final Payment Fee	Future maturities of the Loans, including the final payment fee, as of March 31, 2017 are as follows (in thousands): March 31, 2017 Remainder of 2017 $ 5,400 Year ending December 31, 2018 7,200 Year ending December 31, 2019 4,431 17,031 Unaccreted balance for final payment fee on Loans (870 ) Unamortized discounts (378 ) 15,783 Less current portion (7,200 ) Noncurrent portion $ 8,583

Common Stock, Convertible Pre20

Common Stock, Convertible Preferred Stock and Stockholders’ Deficit (Tables)	3 Months Ended
	Mar. 31, 2017
Equity [Abstract]
Schedule of Changes in Number of Convertible Preferred and Common Stock Outstanding and Total Stockholders' Deficit	Changes in the number of shares of the Company’s convertible preferred and common stock outstanding and total stockholders’ deficit during the three months ended March 31, 2017 were as follows (in thousands, except share amounts): Shares of Convertible Preferred Stock Shares of Common Stock Total Stockholders’ Deficit Balance, December 31, 2016 46,163,605 2,202,517 $ (124,417 ) Stock-based compensation — — 529 Exercise of stock options — 24,648 41 Fractional shares adjustment upon reverse stock split — 2 — Other comprehensive loss — — (1 ) Net loss — — (9,073 ) Balance, March 31, 2017 46,163,605 2,227,167 $ (132,921 )
Schedule of Authorized, Issued and Outstanding Shares, and Liquidation Preferences of Convertible Preferred Stock by Series	The authorized, issued and outstanding shares, and liquidation preferences of convertible preferred stock by series as of March 31, 2017 and December 31, 2016 are as follows (in thousands, except share amounts): Shares Authorized Shares Issued and Outstanding Liquidation Preference Series A 6,700,000 6,700,000 $ 6,700 Series B 8,676,800 8,676,800 10,846 Series C 5,697,601 5,697,601 9,116 Series C-1 1,578,948 1,578,948 3,000 Series D 3,888,375 3,888,375 7,777 Series E 2,485,250 2,485,250 9,941 Series F 5,904,501 5,904,501 25,980 Series G 2,432,068 2,432,068 12,160 Series H 12,000,000 8,800,062 46,200 Undesignated 1,636,457 — — 51,000,000 46,163,605 $ 131,720
Schedule of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance at March 31, 2017 is as follows and excludes shares issuable upon the conversion of all outstanding principal and accrued interest related to convertible promissory notes payable: Issued and Outstanding: Convertible preferred stock (as-converted) 6,690,066 Stock options 1,464,177 Warrants for common stock 724 Warrants for preferred stock (as-converted) 9,936 Shares reserved for future award grants 69,525 Total 8,234,428

Equity Incentive Plan and Sto21

Equity Incentive Plan and Stock-Based Compensation (Tables)	3 Months Ended
	Mar. 31, 2017
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Summary of Stock Option Activity	The following table summarizes stock option activity under the 2009 Plan: Shares Subject to Options Weighted- Average Exercise Price per Share Weighted- Average Remaining Contractual Term (in years) Aggregate Intrinsic (in thousands) Outstanding at December 31, 2016 1,385,855 $ 11.35 Granted 103,934 $ 15.12 Exercised (24,648 ) $ 1.64 Forfeitures and cancellations (964 ) $ 12.11 Outstanding at March 31, 2017 1,464,177 $ 11.78 8.0 $ 3,223 Time-based options at March 31, 2017: Outstanding 1,275,526 $ 11.11 7.7 $ 3,223 Vested and expected to vest 1,275,526 $ 11.11 7.7 $ 3,223 Exercisable 574,746 $ 5.97 5.8 $ 3,221 Performance-based options at March 31, 2017: Outstanding 188,651 $ 16.30 9.7 $ — Vested and expected to vest — $ — — $ — Exercisable — $ — — $ —
Summary of Fair Value of Employee Stock Option Grants	The assumptions used in the Black-Scholes option pricing model to determine the fair value of the employee stock option grants were as follows: Three Months Ended March 31, 2017 Time-Based Vesting Provisions Performance-Based Vesting Provisions Risk-free interest rate 2.17 % 1.98%-2.17% Expected volatility 76.0 % 75.2%-76.3% Weighted-average volatility 76.0 % 75.9 % Dividend yield 0 % 0 % Weighted-average expected term (in years) 6.1 6.3 Weighted-average grant date fair value per share $ 6.79 $ 6.73
Summary of Total Non-Cash Stock-Based Compensation Expense for All Stock Awards, Net of Forfeitures Recognized	Total non-cash stock-based compensation expense for all stock awards, net of forfeitures recognized as they occur, that was recognized in the statements of operations is as follows (in thousands): Three Months Ended March 31, 2017 2016 Research and development $ 142 $ 109 General and administrative 387 156 Total $ 529 $ 265

Organization and Basis of Pre22

Organization and Basis of Presentation - Additional Information (Details)	Apr. 19, 2017USD ($)	Mar. 31, 2017USD ($)Segment	Dec. 31, 2016USD ($)
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Accumulated deficit		$ 137,073,000	$ 128,000,000
Working capital		$ 14,000,000
Number of operating segment | Segment		1
Product revenue		$ 0
Subsequent Event
Organization Consolidation And Presentation Of Financial Statements [Line Items]
Net proceeds from issuance of initial public offering	$ 86,900,000

Summary of Significant Accoun23

Summary of Significant Accounting Policies - Schedule of Common Stock Equivalents from Potentially Dilutive Securities Not Included in Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities not included in calculation of diluted net loss per share	8,164,903	7,422,798
Common Stock Options
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities not included in calculation of diluted net loss per share	1,464,177	722,072
Common Stock Warrant
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities not included in calculation of diluted net loss per share	724	724
Convertible Preferred Stock Warrants (as-converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities not included in calculation of diluted net loss per share	9,936	9,936
Convertible Preferred Stock (as-converted)
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Potential dilutive securities not included in calculation of diluted net loss per share	6,690,066	6,690,066

Summary of Significant Accoun24

Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Accounting Policies [Abstract]
Net unrealized loss on investments	$ (1,000)	$ 54,000

Fair Value of Financial Instr25

Fair Value of Financial Instruments - Summary of Fair Value of Assets and Liabilities Measured on a Recurring Basis (Details) - Fair Value Measured on Recurring Basis - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	$ 21,930	$ 25,735
Preferred Stock Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities	67	126
Quoted Market Prices for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	10,450	2,958
Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities	11,480	22,777
Significant Unobservable Inputs (Level 3) | Preferred Stock Warrant
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Preferred stock warrant liabilities	67	126
U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,869
Marketable securities	10,450	2,958
U.S. Treasury Securities | Quoted Market Prices for Identical Assets (Level 1)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	1,869
Marketable securities	10,450	2,958
Certificates of Deposit
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		240
Marketable securities	11,480	22,777
Certificates of Deposit | Significant Other Observable Inputs (Level 2)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		240
Marketable securities	$ 11,480	$ 22,777

Fair Value of Financial Instr26

Fair Value of Financial Instruments - Additional Information (Details) - USD ($)	Mar. 31, 2017	Dec. 31, 2016	Mar. 31, 2016
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments, transfer of Level 1 to Level 2	$ 0		$ 0
Percentage of increase in fair value of preferred stock	10.00%
Aggregate increase in estimated fair value of preferred stock warrant liabilities	$ 8,000
Aggregate carrying amounts of the convertible notes	11,016,000	$ 3,398,000
Carrying Amount | Significant Unobservable Inputs (Level 3)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Notes payable	15,800,000
Aggregate carrying amounts of the convertible notes	11,000,000
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Investments in money market funds measured at fair value using net asset value per share	$ 3,100,000	$ 2,200,000

Fair Value of Financial Instr27

Fair Value of Financial Instruments - Summary of Activity in Liabilities Measured at Fair Value on Recurring Basis (Details) - Preferred Stock Warrant Liabilities $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Balance at December 31, 2016	$ 126
Gain on warrant valuation included in other income (expense), net	(59)
Balance at March 31, 2017	$ 67

Certain Financial Statement C28

Certain Financial Statement Caption Information - Summary of Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 21,931	$ 25,735
Unrealized Gain	2	6
Unrealized Loss	(3)	(6)
Fair Value	21,930	25,735
Certificates of Deposit | Maturity (in years) 1 or Less
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	9,822	19,299
Unrealized Gain	1	1
Unrealized Loss	(1)	(2)
Fair Value	9,822	19,298
Certificates of Deposit | Maturity More Than 1 Year and Less Than 5 Years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,658	3,478
Unrealized Gain		1
Fair Value	1,658	3,479
U.S. Treasury Securities | Maturity (in years) 1 or Less
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,451	1,678
Unrealized Gain	1
Unrealized Loss	(2)
Fair Value	$ 10,450	1,678
U.S. Treasury Securities | Maturity More Than 1 Year and Less Than 5 Years
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		1,280
Unrealized Gain		4
Unrealized Loss		(4)
Fair Value		$ 1,280

Certain Financial Statement C29

Certain Financial Statement Caption Information - Additional Information (Details)	3 Months Ended
	Mar. 31, 2017USD ($)
Balance Sheet Related Disclosures [Abstract]
Other-than-temporary impairments during period	$ 0

Certain Financial Statement C30

Certain Financial Statement Caption Information - Components of Accrued Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Balance Sheet Related Disclosures [Abstract]
Clinical trial expenses	$ 2,790	$ 2,114
Contract manufacturing services	1,564	1,508
Payroll and other employee-related expenses	1,591	728
Professional fees	1,084	459
Contract research services	91	114
Interest payable	111	120
Other	625	394
Total accrued liabilities	$ 7,856	$ 5,437

Notes Payable - Additional Info

Notes Payable - Additional Information (Details)	Apr. 19, 2017USD ($)$ / sharesshares	Oct. 30, 2015USD ($)Lender	Mar. 31, 2017USD ($)	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Proceeds from convertible promissory notes			$ 7,338,000
Convertible promissory notes subscription liability				$ 140,000
Aggregate carrying amounts of the convertible notes			$ 11,016,000	$ 3,398,000
Subsequent Event
Debt Instrument [Line Items]
Aggregate carrying amounts of the convertible notes	$ 11,100,000
Debt conversion, converted instrument, shares issued | shares	1,109,176
Debt instrument, conversion price | $ / shares	$ 10
Loan Agreement
Debt Instrument [Line Items]
Number of Lenders | Lender		2
Loans		$ 18,000,000
Floating rate of interest			8.25%	8.00%
Debt instrument, interest rate terms			Loan Agreement bear a floating rate of interest equal to the greater of 7.75% or the monthly prime rate plus 4.50%
Debt instrument, frequency of periodic payment			due in monthly principal and interest payments, with final maturity of the Loans in May 2019.
Debt instrument maturity		May 31, 2019
Debt instrument, final payment fee, percentage		7.95%
Deferred debt issuance cost		$ 600,000
Final payment fee		$ 1,400,000
Debt instrument effective interest rate			11.44%	11.19%
Loan Agreement | Minimum
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage		7.75%
Loan Agreement | Prime Rate
Debt Instrument [Line Items]
Debt instrument, basis spread on variable rate		4.50%
Convertible Notes
Debt Instrument [Line Items]
Loans			$ 7,500,000	$ 3,400,000
Debt instrument, interest rate, stated percentage			7.00%
Debt instrument maturity			Nov. 21, 2018
Debt instrument effective interest rate			7.20%	7.54%
Proceeds from convertible promissory notes			$ 10,900,000
Convertible promissory notes subscription liability				$ 140,000
Convertible notes, unamortized discounts			$ 36,000	34,000
Percentage of outstanding principal convertible notes			110.00%
Convertible Notes | Board of Directors
Debt Instrument [Line Items]
Loans			$ 250,000
Aggregate carrying amounts of the convertible notes			1,300,000	1,000,000
Convertible Notes | Chief Executive Officer
Debt Instrument [Line Items]
Loans			10,000
Aggregate carrying amounts of the convertible notes			$ 35,000	$ 25,000
Convertible Notes | Maximum
Debt Instrument [Line Items]
Debt instrument maturity			Nov. 21, 2019

Notes Payable - Schedule of Agg

Notes Payable - Schedule of Aggregate Carrying Amounts of Loans (Details) - Loan Agreement - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Principal	$ 15,600	$ 17,400
Add: accreted liability for final payment fee	561	462
Less: unamortized discount	(378)	(421)
Loans, aggregate carrying amount	$ 15,783	$ 17,441

Notes Payable - Schedule of Fut

Notes Payable - Schedule of Future Maturities Loans Including Final Payment Fee (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Notes payable, net of current portion	$ 8,583	$ 10,241
Loan Agreement
Debt Instrument [Line Items]
Remainder of 2017	5,400
Year ending December 31, 2018	7,200
Year ending December 31, 2019	4,431
Long-term debt at maturity	17,031
Unaccreted balance for final payment fee on Loans	(870)
Less: unamortized discount	(378)	(421)
Loans, aggregate carrying amount	15,783	$ 17,441
Less current portion	(7,200)
Notes payable, net of current portion	$ 8,583

Common Stock, Convertible Pre34

Common Stock, Convertible Preferred Stock and Stockholders' Deficit - Additional Information (Details) - USD ($)	Apr. 19, 2017	Mar. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Stock split description		In March 2017, the Company’s board of directors and stockholders approved a 1-for-6.9 reverse stock split of its outstanding common stock. The accompanying financial statements and notes to the financial statements give retroactive effect to the reverse stock split for all periods presented.
Reverse stock split description		1-for-6.9
Convertible preferred stock, conversion basis		1-for-6.9
Common stock, shares outstanding		2,227,167	2,202,517
Subsequent Event
Class Of Stock [Line Items]
Aggregate proceeds on public offering	$ 86,900,000
Subsequent Event | IPO
Class Of Stock [Line Items]
Aggregate proceeds on public offering	$ 86,900,000
Outstanding shares of convertible preferred stock converted into common stock, shares	6,690,066
Minimum
Class Of Stock [Line Items]
Aggregate proceeds on public offering		$ 10,000,000
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock dividend rate		5.00%

Common Stock, Convertible Pre35

Common Stock, Convertible Preferred Stock and Stockholders' Deficit - Schedule of Changes in Number of Convertible Preferred and Common Stock Outstanding and Total Stockholders' Deficit (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Class Of Stock [Line Items]
Balance, December 31, 2016	$ (124,417)
Stock-based compensation	529
Exercise of stock options	41
Other comprehensive loss	(1)
Net loss	(9,073)	$ (8,006)
Balance, March 31, 2017	$ (132,921)
Convertible Preferred Stock
Class Of Stock [Line Items]
Balance, December 31, 2016, shares	46,163,605
Balance, March 31, 2017, shares	46,163,605
Shares of Common Stock
Class Of Stock [Line Items]
Balance, December 31, 2016, shares	2,202,517
Exercise of stock options, shares	24,648
Fractional shares adjustment upon reverse stock split, shares	2
Balance, March 31, 2017, shares	2,227,167

Common Stock, Convertible Pre36

Common Stock, Convertible Preferred Stock and Stockholders' Deficit - Schedule of Authorized, Issued and Outstanding Shares, and Liquidation Preferences of Convertible Preferred Stock by Series (Details) - USD ($) $ in Thousands	Mar. 31, 2017	Dec. 31, 2016
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	51,000,000	51,000,000
Convertible Preferred Stock, Shares Issued	46,163,605	46,163,605
Convertible Preferred Stock, Shares Outstanding	46,163,605	46,163,605
Convertible Preferred Stock, Liquidation Preference	$ 131,720	$ 131,720
Series A
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	6,700,000	6,700,000
Convertible Preferred Stock, Shares Issued	6,700,000	6,700,000
Convertible Preferred Stock, Shares Outstanding	6,700,000	6,700,000
Convertible Preferred Stock, Liquidation Preference	$ 6,700	$ 6,700
Series B
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	8,676,800	8,676,800
Convertible Preferred Stock, Shares Issued	8,676,800	8,676,800
Convertible Preferred Stock, Shares Outstanding	8,676,800	8,676,800
Convertible Preferred Stock, Liquidation Preference	$ 10,846	$ 10,846
Series C
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	5,697,601	5,697,601
Convertible Preferred Stock, Shares Issued	5,697,601	5,697,601
Convertible Preferred Stock, Shares Outstanding	5,697,601	5,697,601
Convertible Preferred Stock, Liquidation Preference	$ 9,116	$ 9,116
Series C-1
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	1,578,948	1,578,948
Convertible Preferred Stock, Shares Issued	1,578,948	1,578,948
Convertible Preferred Stock, Shares Outstanding	1,578,948	1,578,948
Convertible Preferred Stock, Liquidation Preference	$ 3,000	$ 3,000
Series D
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	3,888,375	3,888,375
Convertible Preferred Stock, Shares Issued	3,888,375	3,888,375
Convertible Preferred Stock, Shares Outstanding	3,888,375	3,888,375
Convertible Preferred Stock, Liquidation Preference	$ 7,777	$ 7,777
Series E
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	2,485,250	2,485,250
Convertible Preferred Stock, Shares Issued	2,485,250	2,485,250
Convertible Preferred Stock, Shares Outstanding	2,485,250	2,485,250
Convertible Preferred Stock, Liquidation Preference	$ 9,941	$ 9,941
Series F
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	5,904,501	5,904,501
Convertible Preferred Stock, Shares Issued	5,904,501	5,904,501
Convertible Preferred Stock, Shares Outstanding	5,904,501	5,904,501
Convertible Preferred Stock, Liquidation Preference	$ 25,980	$ 25,980
Series G
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	2,432,068	2,432,068
Convertible Preferred Stock, Shares Issued	2,432,068	2,432,068
Convertible Preferred Stock, Shares Outstanding	2,432,068	2,432,068
Convertible Preferred Stock, Liquidation Preference	$ 12,160	$ 12,160
Series H
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	12,000,000	12,000,000
Convertible Preferred Stock, Shares Issued	8,800,062	8,800,062
Convertible Preferred Stock, Shares Outstanding	8,800,062	8,800,062
Convertible Preferred Stock, Liquidation Preference	$ 46,200	$ 46,200
Undesignated
Temporary Equity [Line Items]
Convertible Preferred Stock, Shares Authorized	1,636,457	1,636,457

Common Stock, Convertible Pre37

Common Stock, Convertible Preferred Stock and Stockholders' Deficit - Schedule of Common Stock Reserved for Future Issuance (Details)	Mar. 31, 2017shares
Class Of Stock [Line Items]
Common stock reserved for future issuance	8,234,428
Warrants
Class Of Stock [Line Items]
Common stock reserved for future issuance	724
Convertible Preferred Stock (as-converted)
Class Of Stock [Line Items]
Common stock reserved for future issuance	6,690,066
Stock Options
Class Of Stock [Line Items]
Common stock reserved for future issuance	1,464,177
Shares Reserved for Future Award Grants
Class Of Stock [Line Items]
Common stock reserved for future issuance	69,525
Warrants for Preferred Stock (as-converted)
Class Of Stock [Line Items]
Common stock reserved for future issuance	9,936

Equity Incentive Plan and Sto38

Equity Incentive Plan and Stock-Based Compensation - Additional Information (Details) - USD ($)	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016	Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares available for future grants	8,234,428
Total fair value of options vested	$ 1,000,000	$ 200,000
Aggregate intrinsic value, options exercised during the period	300,000	$ 9,000
Unrecognized compensation expense	$ 7,400,000
Weighted-average period over which unrecognized compensation expense is expected to be recognized	3 years
Performance-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options outstanding	188,651
2009 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares of common stock reserved under the plan	1,533,702
Number of shares reserved for issuance upon exercise of granted and outstanding stock options	1,464,177
Shares available for future grants	69,525
Stock options expiration term	10 years
Stock options outstanding	1,464,177		1,385,855
2009 Equity Incentive Plan | Time-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting period	4 years
Stock options remaining vesting period	36 months
Stock options outstanding	1,275,526
2009 Equity Incentive Plan | Performance-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting description	Grants with performance-based vesting provisions vest upon the achievement of three separate development and regulatory milestones, with one-third of the options vesting upon the achievement of each milestone.
Stock options outstanding	188,651
2009 Equity Incentive Plan | Vesting After First Year | Time-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock options vesting percentage	25.00%

Equity Incentive Plan and Sto39

Equity Incentive Plan and Stock-Based Compensation - Summary of Stock Option Activity (Details) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2017USD ($)$ / sharesshares
Performance-based Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Subject to Options, Outstanding at March 31, 2017	188,651
2009 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Subject to Options, Outstanding at December 31, 2016	1,385,855
Shares Subject to Options, Granted	103,934
Shares Subject to Options, Exercised	(24,648)
Shares Subject to Options, Forfeitures and cancellations	(964)
Shares Subject to Options, Outstanding at March 31, 2017	1,464,177
Weighted-Average Exercise Price per Share, Outstanding at December 31, 2016 | $ / shares	$ 11.35
Weighted-Average Exercise Price per Share, Granted | $ / shares	15.12
Weighted-Average Exercise Price per Share, Exercised | $ / shares	1.64
Weighted-Average Exercise Price per Share, Forfeitures and cancellations | $ / shares	12.11
Weighted-Average Exercise Price per Share, Outstanding at March 31, 2017 | $ / shares	$ 11.78
Weighted-Average Remaining Contractual Term, Outstanding at March 31, 2017	8 years
Aggregate Intrinsic Value, Outstanding at March 31, 2017 | $	$ 3,223
2009 Equity Incentive Plan | Time-based Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Subject to Options, Outstanding at March 31, 2017	1,275,526
Shares Subject to Options, Vested and expected to vest	1,275,526
Shares Subject to Options, Exercisable	574,746
Weighted-Average Exercise Price per Share, Outstanding at March 31, 2017 | $ / shares	$ 11.11
Weighted-Average Exercise Price per Share, Vested and expected to vest | $ / shares	11.11
Weighted-Average Exercise Price per Share, Exercisable | $ / shares	$ 5.97
Weighted-Average Remaining Contractual Term, Outstanding at March 31, 2017	7 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	7 years 8 months 12 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 9 months 18 days
Aggregate Intrinsic Value, Outstanding at March 31, 2017 | $	$ 3,223
Aggregate Intrinsic Value, Vested and expected to vest | $	3,223
Aggregate Intrinsic Value, Exercisable | $	$ 3,221
2009 Equity Incentive Plan | Performance-based Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares Subject to Options, Outstanding at March 31, 2017	188,651
Weighted-Average Exercise Price per Share, Outstanding at March 31, 2017 | $ / shares	$ 16.30
Weighted-Average Remaining Contractual Term, Outstanding at March 31, 2017	9 years 8 months 12 days

Equity Incentive Plan and Sto40

Equity Incentive Plan and Stock-Based Compensation - Summary of Fair Value of Employee Stock Option Grants (Details)	3 Months Ended
	Mar. 31, 2017$ / shares
Time-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate	2.17%
Expected volatility	76.00%
Weighted-average volatility	76.00%
Dividend yield	0.00%
Weighted-average expected term (in years)	6 years 1 month 6 days
Weighted-average grant date fair value per share	$ 6.79
Performance-Based Vesting Provisions
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk-free interest rate, minimum	1.98%
Risk-free interest rate, maximum	2.17%
Expected volatility, minimum	75.20%
Expected volatility, maximum	76.30%
Weighted-average volatility	75.90%
Dividend yield	0.00%
Weighted-average expected term (in years)	6 years 3 months 18 days
Weighted-average grant date fair value per share	$ 6.73

Equity Incentive Plan and Sto41

Equity Incentive Plan and Stock-Based Compensation - Summary of Total Non-Cash Stock-Based Compensation Expense for All Stock Awards, Net of Forfeitures Recognized (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total non-cash stock-based compensation expense	$ 529	$ 265
Research and Development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total non-cash stock-based compensation expense	142	109
General and Administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total non-cash stock-based compensation expense	$ 387	$ 156

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	Apr. 19, 2017	Mar. 31, 2017	Mar. 31, 2017	Apr. 12, 2017	Dec. 31, 2016
Subsequent Event [Line Items]
Common stock, shares authorized		77,800,000	77,800,000		77,800,000
Common stock, par value		$ 0.001	$ 0.001		$ 0.001
Common stock reserved for future issuance		8,234,428	8,234,428
2017 Employee Stock Purchase Plan
Subsequent Event [Line Items]
Increase in percentage of number of shares of common stock reserved for issuance		1.00%
Shares of common stock authorized under ESPP		250,000	250,000
Annual increase in number of shares of common stock reserved for issuance		300,000
2017 Equity Incentive Plan
Subsequent Event [Line Items]
Common stock reserved for future issuance		1,600,000	1,600,000
Increase in percentage of number of shares of common stock reserved for issuance			4.00%
2009 Equity Incentive Plan
Subsequent Event [Line Items]
Common stock reserved for future issuance		69,525	69,525
Shares of common stock authorized under ESPP		1,533,702	1,533,702
IPO
Subsequent Event [Line Items]
Payments for underwriting discounts, commissions and estimated offering costs			$ 0.3
Subsequent Event
Subsequent Event [Line Items]
Estimated net proceeds from issuance of initial public offering after underwriting discounts, commissions and estimated offering	$ 86.9
Conversion of convertible notes into common stock	1,109,176
Conversion of convertible notes price, per share	$ 10
Subsequent Event | 2009 Equity Incentive Plan
Subsequent Event [Line Items]
Common stock reserved for future issuance				75,517
Subsequent Event | IPO
Subsequent Event [Line Items]
Completion date of initial public offering	April 19, 2017
Common stock issued, shares	9,775,000
Shares price, per share	$ 10
Estimated net proceeds from issuance of initial public offering after underwriting discounts, commissions and estimated offering	$ 86.9
Payments for underwriting discounts, commissions and estimated offering costs	$ 10.9
Outstanding shares of convertible preferred stock converted into common stock, shares	6,690,066
Warrants to purchase shares of common stock	9,936
Warrant to purchase common stock, exercise price	$ 36.23
Aggregate principal and accrued interest, conversion of notes amount	$ 11.1
Conversion of convertible notes into common stock	1,109,176
Conversion of convertible notes price, per share	$ 10
Common stock, shares authorized	200,000,000
Common stock, par value	$ 0.001
Preferred stock, shares authorized	10,000,000
Preferred stock, par value	$ 0.001