TRACON Pharmaceuticals (TCON) 10-Q 14 May 19 2019 Q1 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	3 Months Ended
	Mar. 31, 2019	May 10, 2019
Document And Entity Information [Abstract]
Entity Registrant Name	Tracon Pharmaceuticals, Inc.
Entity Central Index Key	0001394319
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Small Business	true
Entity Ex Transition Period	true
Entity Common Stock, Shares Outstanding		29,937,457
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Trading Symbol	TCON

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 22,085	$ 25,136
Short-term investments	9,984	13,968
Prepaid and other assets	1,019	1,499
Total current assets	33,088	40,603
Property and equipment, net	38	45
Other assets	1,061
Total assets	34,187	40,648
Current liabilities:
Accounts payable and accrued expenses	11,034	10,947
Accrued compensation and related expenses	714	1,464
Long-term debt, current portion	1,806	1,084
Total current liabilities	13,554	13,495
Other long-term liabilities	1,124	368
Long-term debt, less current portion	4,704	5,343
Commitments and contingencies (Note 4)
Stockholders’ equity:
Preferred stock, $0.001 par value, authorized shares — 10,000,000 at March 31, 2019 and December 31, 2018; issued and outstanding shares — none
Common stock, $0.001 par value; authorized shares — 200,000,000 at March 31, 2019 and December 31, 2018; issued and outstanding shares — 29,898,698 and 29,871,327 at March 31, 2019 and December 31, 2018, respectively	30	30
Additional paid-in capital	161,648	161,072
Accumulated deficit	(146,873)	(139,660)
Total stockholders’ equity	14,805	21,442
Total liabilities and stockholders’ equity	$ 34,187	$ 40,648

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Mar. 31, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Preferred Stock, Par or Stated Value Per Share	$ 0.001	$ 0.001
Preferred Stock, Shares Authorized	10,000,000	10,000,000
Preferred Stock, Shares Issued	0	0
Preferred Stock, Shares Outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	29,898,698	29,871,327
Common stock, shares outstanding	29,898,698	29,871,327

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 0	$ 3,000
Type of Revenue [Extensible List]	tcon:CollaborationMember	tcon:CollaborationMember
Operating expenses:
Research and development	$ 5,214	$ 9,438
General and administrative	1,949	1,751
Total operating expenses	7,163	11,189
Loss from operations	(7,163)	(8,189)
Other expense:
Interest expense, net	(46)	(169)
Other expense, net	(4)	(6)
Total other expense	(50)	(175)
Net loss	$ (7,213)	$ (8,364)
Net loss per share, basic and diluted	$ (0.24)	$ (0.46)
Weighted-average shares outstanding, basic and diluted	29,892,007	18,214,787

Condensed Consolidated Statemen

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Cash flows from operating activities
Net loss	$ (7,213)	$ (8,364)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	596	706
Depreciation and amortization	7	7
Noncash interest	61	79
Amortization of debt discount	21	27
Amortization of premium/discount on short-term investments	(36)	(1)
Deferred rent		7
Lease asset amortization and liability accretion, net	2
Deferred revenue		(3,000)
Changes in assets and liabilities:
Prepaid expenses and other assets	480	289
Accounts payable and accrued expenses	(219)	3,756
Accrued compensation and related expenses	(750)	239
Net cash used in operating activities	(7,051)	(6,255)
Cash flows from investing activities
Purchases of available-for-sale short-term investments	(4,980)
Proceeds from the maturity of available-for-sale short-term investments	9,000	5,000
Net cash provided by investing activities	4,020	5,000
Cash flows from financing activities
Repayment of long-term debt		(800)
Proceeds from sale of common stock and warrants, net of offering costs		35,159
Payment of tax withholdings related to net share settlements of vested restricted stock awards	(20)	(78)
Net cash (used in) provided by financing activities	(20)	34,281
(Decrease) increase in cash and cash equivalents	(3,051)	33,026
Cash and cash equivalents at beginning of period	25,136	29,467
Cash and cash equivalents at end of period	$ 22,085	$ 62,493

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	3 Months Ended
	Mar. 31, 2019
Organization And Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	1. Organization and Summary of Significant Accounting Policies Organization and Business TRACON Pharmaceuticals, Inc. (formerly Lexington Pharmaceuticals, Inc.) (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a clinical stage biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer and, through its license to Santen Pharmaceutical Co. Ltd. (Santen), wet age-related macular degeneration, or wet AMD. The Company’s product development platform, which emphasizes capital efficiency, also provides to ex-U.S. companies a rapid and capital-efficient U.S. drug development solution that includes U.S. and European Union (EU) clinical development expertise and U.S. commercialization expertise. The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, TRACON Pharma Limited and TRACON Pharma International Limited, which were formed in September 2015 and January 2019, respectively, and are currently inactive. All significant intercompany accounts and transactions have been eliminated. Basis of Presentation As of March 31, 2019, the Company has devoted substantially all of its efforts to product development, raising capital, and building infrastructure and has not realized revenues from its planned principal operations. The Company has incurred operating losses since inception. As of March 31, 2019, the Company had an accumulated deficit of $146.9 million. The Company anticipates that it will continue to incur net losses into the foreseeable future as it continues the development and commercialization of its product candidates and works to develop additional product candidates through research and development programs. At March 31, 2019, the Company had cash, cash equivalents, and short-term investments of $32.1 million. Based on the Company’s current business plan, management believes that there is substantial doubt as to whether existing cash, cash equivalents, and short-term investments will be sufficient to meet its obligations as they become due within one year from the date these financial statements are issued. The Company’s ability to execute its operating plan through 2020 and beyond depends on its ability to obtain additional funding through equity offerings, debt financings, or potential licensing and collaboration arrangements. The accompanying unaudited condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, the Company’s current working capital, anticipated operating expenses and net losses, and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, raise substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. The unaudited condensed consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through cash, cash equivalents, and investments on hand, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements, including equity financing through the common stock purchase agreement the Company entered into with Aspire Capital Fund, LLC in March 2017 for the purchase of up to $21.0 million of the Company’s common stock over a 30 month period and/or the Capital on Demand TM Unaudited Interim Financial Information The unaudited condensed consolidated financial statements at March 31, 2019, and for the three months ended March 31, 2019 and 2018, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC), and with accounting principles generally accepted in the United States (GAAP) applicable to interim financial statements. These unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, consisting of only normal recurring accruals, which in the opinion of management are necessary to present fairly the Company’s financial position as of the interim date and results of operations for the interim periods presented. Interim results are not necessarily indicative of results for a full year or future periods. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2018, included in its Annual Report on Form 10-K filed with the SEC on March 1, 2019. Use of Estimates The Company’s condensed consolidated financial statements are prepared in accordance with GAAP. The preparation of the Company’s condensed consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenue, and expenses. The most significant estimates in the Company’s financial statements relate to revenue recognition, expenses incurred for clinical trials, and the valuation of equity awards. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions. Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of three months or less at the date of purchase. The carrying amounts approximate fair value due to the short maturities of these investments. Cash and cash equivalents include cash in readily available checking and money market funds. Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents, and investments. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held. Revenue Recognition To date, substantially all of the Company’s revenue has been derived from its license agreements with Santen and Ambrx, Inc. (Ambrx) as described in Note 6. The terms of these arrangements include payments to the Company for the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. In accordance with ASU 2014-09, the Company performs the following five steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the contract(s) with a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services transferred to the customer. Once a contract is determined to be within the scope of Accounting Standards Codification 606, Revenue from Contracts with Customers, at contract inception, the Company assesses the goods or services promised within the contract to determine those that are performance obligations and assesses whether each promised good is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization, and regulatory milestone payments, the Company evaluates whether the achievement of the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. Performance milestone payments represent a form of variable consideration. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Achievement of milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable until the approvals are achieved. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis and the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations at the outset of the arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its collaborators based on billing schedules established in each contract. Up-front and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less. Clinical Trial Expense Accruals As part of the process of preparing the Company’s financial statements, the Company is required to estimate expenses resulting from its obligations under contracts with vendors, clinical sites, contract research organizations (CROs), and consultants in connection with conducting clinical trials. The financial terms of these contracts vary and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its financial statements by recording those expenses in the period in which services are performed and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with the clinical sites and applicable personnel and outside service providers as to the progress or state of consummation of trials. During the course of a clinical trial, the Company adjusts the clinical expense recognition if actual results differ from its estimates. The Company makes estimates of accrued expenses as of each balance sheet date based on the facts and circumstances known at that time. The Company’s clinical trial accruals are dependent upon accurate reporting by clinical sites, CROs, and other third-party vendors. Although the Company does not expect its estimates to differ materially from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting amounts that are too high or too low for any particular period. For the three months ended March 31, 2019 and 2018, there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of stock option grants, employee restricted stock unit grants (RSUs), and employee stock purchase plan (ESPP) rights recognized as expense over the requisite service period of the awards (usually the vesting period) on a straight-line basis. The Company estimates the fair value of stock option grants and ESPP rights using the Black-Scholes option pricing model. The fair value of RSUs is based on the stock price on the date of grant. Equity award forfeitures are recorded as they occur. Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented. Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average shares of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of common shares outstanding that are subject to repurchase. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. 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. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Three Months Ended March 31, 2019 2018 Warrants to purchase common stock 15,619,113 14,326,537 Common stock options and restricted stock units 4,509,499 3,111,882 ESPP shares — 8,579 20,128,612 17,446,998 Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are included in Other assets, Accounts payable and accrued expenses, and Other long-term liabilities within the consolidated balance sheet as of March 31, 2019. The Company currently does not have any finance leases. Operating lease right-of-use (ROU) assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term. Recently Adopted Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting Compensation-Stock Compensation

Short-Term Investments, Cash Eq

Short-Term Investments, Cash Equivalents and Fair Value Measurements	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Short-Term Investments, Cash Equivalents and Fair Value Measurements	2. Short-Term Investments, Cash Equivalents and Fair Value Measurements At March 31, 2019, short-term investments consisted of U.S. treasury securities. The Company classifies all investments as available-for-sale securities, as the sale of such investments may be required prior to maturity to implement management strategies. These investments are carried at amortized cost which approximates fair value. A decline in the market value of any short-term investment below cost that is determined to be other-than-temporary will result in a revaluation of its carrying amount to fair value. The impairment is charged to earnings and a new cost basis for the security is established. No such impairment charges were recorded for any period presented. Realized gains and losses from the sale of short-term investments, if any, are determined on a specific identification basis. Realized gains and losses and declines in value judged to be other-than-temporary, if any, on available-for-sale securities are included in other income or expense on the consolidated statements of operations. Realized and unrealized gains and losses during the periods presented were immaterial. Premiums and discounts are amortized or accreted over the life of the related security as an adjustment to yield using the straight-line method and are included in interest income on the consolidated statements of operations. Interest and dividends on securities classified as available-for-sale are included in interest income on the consolidated statements of operations. At March 31, 2019, the remaining contractual maturities of all available-for-sale investments were less than one year. The carrying amounts of cash and cash equivalents, prepaid and other assets, accounts payable and accrued liabilities are considered to be representative of their respective fair values because of the short-term nature of those instruments. Based on the borrowing rates currently available to the Company for loans with similar terms, which is considered a Level 2 input, the Company believes that the fair value of long-term debt approximates its carrying value. The 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 accounting guidance establishes a three-tier fair value hierarchy, which 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. Level 3: Unobservable inputs in which there is little or no market data, which require the reporting entity to develop its own assumptions. Assets and liabilities are classified based on the lowest level of input that is significant to the fair value measurements. None of the Company’s non-financial assets or liabilities are recorded at fair value on a non-recurring basis. No transfers between levels have occurred during the periods presented. Cash equivalents, which are classified as equity securities, and short-term investments, which are classified as available-for-sale securities, consisted of the following (in thousands): March 31, 2019 December 31, 2018 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 900 $ — $ — $ 900 $ 5,832 $ — $ — $ 5,832 U.S. treasury securities 13,982 — — 13,982 13,968 — — 13,968 $ 14,882 $ — $ — $ 14,882 $ 19,800 $ — $ — $ 19,800 Classified as: Cash equivalents $ 4,898 $ 5,832 Short-term investments 9,984 13,968 Total Cash equivalents and Short-term investments $ 14,882 $ 19,800 The fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets Other Significant for Identical Observable Unobservable Assets Inputs Inputs Total (Level 1) (Level 2) (Level 3) At March 31, 2019 Money market funds and U.S. treasury securities, included in Cash equivalents and Short-term investments $ 14,882 $ — $ 14,882 $ — At December 31, 2018 Money market funds and U.S. treasury securities, included in Cash equivalents and Short-term investments $ 19,800 $ — $ 19,800 $ —

Long-Term Debt

Long-Term Debt	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Long-Term Debt	3 . Long-Term Debt Long-term debt and unamortized debt discount balances were as follows (in thousands): March 31, December 31, 2019 2018 Long-term debt $ 7,000 $ 7,000 Less debt discount, net of current portion (196) (257) Long-term debt, net of debt discount 6,804 6,743 Less current portion of long-term debt (2,100) (1,400) Long-term debt, net of current portion $ 4,704 $ 5,343 Current portion of long-term debt $ 2,100 $ 1,400 Current portion of debt discount (294) (316) Current portion of long-term debt, net $ 1,806 $ 1,084 In May 2018, the Company entered into a third amendment to its Amended and Restated Loan and Security Agreement with Silicon Valley Bank (the 2018 Amended SVB Loan) under which the Company borrowed $7.0 million, all of which was immediately used to repay the Company’s existing loan with SVB (the 2017 Amended SVB Loan). In accordance with the terms of the 2017 Amended SVB Loan, the Company paid a final payment of $0.3 million associated with the payoff of the 2017 Amended SVB Loan. The transaction was accounted for as a debt modification. The 2018 Amended SVB Loan provides for interest to be paid at a rate of 9.0 30 months 4.0% The 2018 Amended SVB Loan provides for prepayment fees of 2.0% 1.0% of the amount prepaid if the prepayment occurs thereafter. The 2018 Amended SVB Loan is collateralized by substantially all of the Company’s assets, other than the Company’s intellectual property, and 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 the Company’s 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 2018 Amended SVB Loan. As of March 31, 2019, In connection with the 2018 Amended SVB Loan, the Company issued SVB a warrant to purchase 53,639 shares of its common stock at an exercise price of $2.61 per share. The warrant is fully exercisable and expires on May 3, 2025. The fair value of the warrant and the final payment related to the 2018 Amended SVB Loan were recorded as debt discounts and are being amortized to interest expense using the effective interest method over the term of the debt, in addition to the remaining unamortized discounts related to the 2017 Amended SVB Loan. At March 31, 2019, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 May 25, 2025 53,639 $ 2.61 157,504 Future minimum principal and interest payments under the 2018 Amended SVB Loan, including the final payment, are as follows (in thousands): Remaining 2019 1,855 2020 3,195 2021 3,218 8,268 Less interest and final payment (1,268) Long-term debt $ 7,000

Commitments and Contingencies

Commitments and Contingencies	3 Months Ended
	Mar. 31, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	4 . Commitments and Contingencies Lonza Biologics Tuas Pte Ltd (Lonza) On February 22, 2017, the Company entered into a long-term manufacturing agreement (Manufacturing Agreement) with Lonza for the long term manufacture and supply of registration and commercial batches of TRC105. Under the Manufacturing Agreement, Lonza agreed to manufacture TRC105 pursuant to purchase orders and in accordance with the manufacturing specifications agreed upon between the Company and Lonza. Following the announcement of the TAPPAS interim unblinded safety and efficacy data in April 2019, the Company exercised its right to terminate the Manufacturing Agreement as a result of its decision to terminate further TRC105 development in oncology. As a result of the discontinuation of TRC105, costs associated with certain batches prior to regulatory approval and batches following regulatory approval will not be incurred, however the Company will be obligated to pay for any costs incurred associated with work completed to date. At March 31, 2019, the Company had estimated non-cancelable purchase obligations totaling $1.1 million under this agreement. License Agreements The Company has entered into various license agreements pursuant to which the Company acquired licenses to certain intellectual property. The agreements generally required an upfront license fee and, in some cases, reimbursement of patent costs. Additionally, under each agreement, the Company may be required to pay annual maintenance fees, royalties, milestone payments and/or sublicensing fees. Each of the license agreements is generally cancelable by the Company, given appropriate prior written notice. At March 31, 2019, potential future milestone payments under these agreements, including future milestone payments associated with TRC253 acquired from Janssen Pharmaceutica N.V. (Janssen) should they not exercise their option to regain their rights to certain assets as discussed in Note 6,

Stockholders' Equity

Stockholders' Equity	3 Months Ended
	Mar. 31, 2019
Stockholders Equity Note [Abstract]
Stockholders' Equity	5 . Stockholders’ Equity Stockholders’ Equity The following tables present the changes in stockholders’ equity (in thousands, except share data): Three Months Ended March 31, 2019 Additional Total Common Stock Paid-in Accumulated Stockholders’ Shares Amount Capital Deficit Equity Balance at December 31, 2018 29,871,327 $ 30 $ 161,072 $ (139,660 ) $ 21,442 Issuance of common stock under equity plans 27,371 — (20 ) — (20) Stock-based compensation expense — — 596 — 596 Net loss — — — (7,213 ) (7,213) Balance at March 31, 2019 29,898,698 $ 30 $ 161,648 $ (146,873 ) $ 14,805 Three Months Ended March 31, 2018 Additional Total Common Stock Paid-in Accumulated Stockholders’ Shares Amount Capital Deficit Equity Balance at December 31, 2017 17,711,928 $ 18 $ 121,670 $ (104,701 ) $ 16,987 Issuance of common stock under equity plans 38,019 — (78 ) — (78) Stock-based compensation expense — — 706 — 706 Vested shares related to repurchase liability — — 3 — 3 Issuances of common stock and warrants, net of offering costs 10,691,588 10 33,225 — 33,235 Net loss — — — (8,364 ) (8,364) Balance at March 31, 2018 28,441,535 $ 28 $ 155,526 $ (113,065 ) $ 42,489 Sales of Common Stock In March and April 2018, the Company sold 11,930,525 shares of its common stock at a purchase price of $2.70 per share, warrants to purchase 1,765,542 shares of its common stock at a purchase price of $2.69 per share and an exercise price of $0.01 per share (the Pre-Funded Warrants) and warrants to purchase 13,696,067 shares of its common stock at a purchase price of $0.125 per share and an exercise price of $2.70 per share (the Common Warrants) for net proceeds of approximately $36.5 million in a private placement to new and certain existing accredited investors. In accordance with their terms, the Pre-Funded Warrants and the Common Warrants may not be exercised if the holder’s ownership of the Company’s common stock would exceed 9.99% or 19.99% of the Company’s total shares outstanding following such exercise, depending on the investor. Both the Pre-Funded Warrants and the Common Warrants were recorded as a component of stockholders’ equity within additional paid-in capital. In April 2018, in connection with this transaction, the Company paid Angel Pond Capital, an affiliate of a holder of more than 5% of the Company’s common stock and an affiliate of a member of the Company’s Board of the Directors, a fee totaling approximately $1.9 million as consideration for acting as a nonexclusive placement agent for this financing. At-The-Market Issuance Sales Agreement In September 2018, the Company entered into the Sales Agreement, as amended in February 2019, with JonesTrading, pursuant to which it may sell from time to time, at its option, up to an aggregate of $8.0 million of the Company’s shares of its common stock through JonesTrading, as sales agent. The Company is required to pay JonesTrading 2.5% of gross proceeds for the common stock sold through the Sales Agreement. During the three months ended March 31, 2019, the Company sold no shares of common stock through the Sales Agreement with JonesTrading and $8.0 million of common stock remains available for sale under the Sales Agreement. In September 2018, the Company terminated its At-the-Market Equity Offering Sales Agreement (Stifel Sales Agreement) with Stifel, Nicolaus & Company, Incorporated (Stifel). The Company had sold an aggregate of approximately $3.5 million of common stock through Stifel pursuant to the Stifel Sales Agreement prior to termination. Equity Plan Activity During the three months ended March 31, 2019, t he Company issued shares of common stock upon the exercise of outstanding stock options and 27,371 shares of common stock upon the vesting of restricted stock units. The Company withheld 18,934 shares of common stock on the vesting date of certain restricted stock units to settle the employees’ minimum statutory tax obligations for income and other related employment taxes, the payment of which is reported as a financing activity in the unaudited condensed consolidated statement of cash flows for the three months ended March 31, 2019. During the year ended December 31, 2018, the Company issued 136,720 shares of common stock upon the exercise of outstanding stock options and 38,019 shares of common stock upon the vesting of restricted stock units. Common Stock Warrants As of March 31, 2019 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 March 27, 2024 13,696,067 $ 2.70 March 27, 2025 1,765,542 $ 0.01 May 3, 2025 53,639 $ 2.61 15,619,113 During the three months ended March 31, 2019 and year ended December 31, 2018, no warrants were exercised. Stock-Based Compensation Expense The weighted-average 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, 2019 2018 Risk-free interest rate 2.6 % 2.8% Expected volatility 81 % 79% Expected term (in years) 6.3 6.3 Expected dividend yield — % —% Stock compensation expense for the ESPP was immaterial for the three months ended March 31, 2019 and 2018. The allocation of stock-based compensation expense was as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 316 $ 364 General and administrative 280 342 $ 596 $ 706

Collaborations

Collaborations	3 Months Ended
	Mar. 31, 2019
Collaborations Disclosure [Abstract]
Collaborations	6 . Collaborations I-Mab In November 2018, the Company and I-Mab Biopharma (I-Mab) entered into separate strategic collaboration and clinical trial agreements (the Collaboration Agreements) for the development of programs for multiple immuno-oncology product candidates, including I-Mab’s proprietary CD73 antibody TJ004309 (the TJ004309 Agreement) as well as up to five proprietary bispecific antibodies currently under development by I-Mab (the Bispecific Agreement). No consideration was exchanged in the Collaboration Agreements. Given the early preclinical stage of development of these assets as of the agreement date, no value was assigned to the Collaboration Agreements in the accompanying consolidated balance sheet. TJ004309 Agreement Pursuant to the TJ004309 Agreement, the Company and I-Mab will collaborate on developing the TJ004309 antibody, with the Company bearing the costs of filing an IND and for Phase 1 clinical trials, with the parties sharing costs equally for Phase 2 clinical trials, and with the Company and I-Mab bearing 40% and 60%, respectively, of the costs for pivotal clinical trials. I-Mab will be responsible for the cost of certain non-clinical activities, the drug supply of TJ004309, and any reference drugs used in the clinical trials. Each of the parties also agreed for a specified period of time to not develop or license to or from a third party any monoclonal antibody targeting CD73 or any other biologic for certain indications that a joint steering committee (JSC), as set up under the TJ004309 Agreement, selects for TJ004309 development. In the event that I-Mab out-licenses the rights to TJ004309 to a third party, the Company would be entitled to receive escalating portions of royalty and non-royalty consideration received by I-Mab with respect to certain territories outside of Greater China. In the event that I-Mab commercializes TJ004309, the Company would be entitled to receive a royalty percentage on net sales by I-Mab in North America ranging from the mid-single digits to low double digits, and in the EU and Japan in the mid-single digits. The portions of certain third party royalty and non-royalty consideration and the royalty from net sales by I-Mab to which the Company would be entitled will escalate based on the phase of development and relevant clinical trial obligations the Company completes under the TJ004309 Agreement, ranging from a high-single digit to a mid-teen percentage of non-royalty consideration as well as a double digit percentage of royalty consideration. The TJ004309 TJ004309 TJ004309 TJ004309 Bispecific Agreement Pursuant to the Bispecific Agreement, the Company and I-Mab may mutually select through a JSC up to five of I-Mab’s bispecific antibody product candidates within a five-year period for development and commercialization in North America. For each product candidate selected by the JSC for development under the Bispecific Agreement, I-Mab will be responsible and bear the costs for IND-enabling studies and establishing manufacturing for the product candidate, while the Company will be responsible for and bear the costs of filing an IND and conducting Phase 1 and Phase 2 clinical studies, and the Company will be responsible for and will share equally with I-Mab in the costs of conducting Phase 3 or pivotal clinical studies, in each case within North America. Subject to I-Mab’s right to co-promote an approved product candidate, the Company will be responsible for commercializing any approved product candidates in North America and will share profits and losses equally with I-Mab in North America. The Company would also be entitled to tiered low single digit royalties on net sales of product candidates in the EU and Japan. At any time prior to completing the first pivotal clinical study for a product candidate or if I-Mab ceases to support development costs or pay its portion of Phase 3 clinical study costs for a product candidate or the JSC decides to cease development over the Company’s objections after initiating Phase 3 clinical studies, the Company will have an option to obtain an exclusive license to such product candidate in all territories except Greater China and Korea, and any other territories in which I-Mab previously licensed rights to a third party subject to the Company’s right of first refusal for any licenses I-Mab may grant to third-parties. If the Company exercises the option, it would assume sole responsibility for developing and commercializing the product candidate in the licensed territory, and in lieu of profit or loss sharing with I-Mab with respect to such product candidate, the Company would owe I-Mab pre-specified upfront and milestone payments and royalties on net sales, with the payments and royalties escalating depending on the phase of development the product candidate reached at the time the Company obtained the exclusive license as follows: (i) if before IND-enabling studies and the preparation of the CMC activities of the collaborative product, the Company would owe I-Mab a one-time upfront payment of $10.0 million, development and regulatory based milestone payments totaling up to $90.0 million that begin upon completion of a pivotal study, sales milestones totaling up to $250.0 million, and royalties in the mid-single digits on annual net sales; (ii) if after IND submission but before completion of a Phase 1a study of the collaborative product, the Company would owe I-Mab a one-time upfront payment of $25.0 million, development and regulatory based milestone payments totaling up to $125.0 million that begin upon completion of a pivotal study, sales milestones totaling up to $250.0 million, and royalties in the high single digits on annual net sales; (iii) if after completion of a Phase 1a study but before completion of Phase 2 proof of concept study for the collaborative product, the Company would owe I-Mab a one-time upfront payment of $50.0 million, development and regulatory based milestone payments totaling up to $250.0 million that begin upon completion of a pivotal study, sales milestones totaling up to $250.0 million, and royalties in the low double digits on annual net sales; and (iv) if after completion of Phase 2 proof of concept study and before completion of pivotal study for the collaborative product, the Company would owe I-Mab a one-time upfront payment of $80.0 million, development and regulatory based milestone payments totaling up to $420.0 million that begin upon completion of a pivotal study, sales milestones totaling up to $250.0 million, and royalties in the high-teen double digits on annual net sales. Each party agreed that for a specified period of time, it would not develop or license to or from any third party any bispecific monoclonal antibody targeting the same two biological targets as those of any selected product candidates under the Bispecific Agreement. If development of any selected product candidates is terminated by a decision of the JSC, all rights to the product candidate will revert to I-Mab, subject to the Company’s right to obtain an exclusive license in certain circumstances. If development is terminated after submission of an IND and prior to initiating Phase 3 clinical studies or after initiating Phase 3 clinical studies and with the Company’s concurrence, the Company would be entitled to tiered low single digit royalties on net sales of the product candidate in North America, the EU, and Japan. The Bispecific Agreement may be terminated by either party in the event of an uncured material breach by the other party, bankruptcy of the other party, or with respect to any selected product candidate, for safety reasons related to that product candidate. Santen In March 2014, the Company entered into a license agreement with Santen, under which the Company granted Santen an exclusive, worldwide license to certain patents, information and know-how related to carotuximab. Under the agreement, Santen is permitted to use, develop, manufacture and commercialize carotuximab products for ophthalmology indications, excluding systemic treatment of ocular tumors. Santen also has the right to grant sublicenses to affiliates and third party collaborators. In the event Santen sublicenses any of its rights under the agreement, Santen will be obligated to pay the Company a portion of any upfront and certain milestone payments received under such sublicense. Santen has sole responsibility for funding, developing, seeking regulatory approval for and commercializing carotuximab products in the field of ophthalmology. In the event that Santen fails to meet certain commercial diligence obligations, the Company will have the option to co-promote carotuximab products in the field of ophthalmology in the United States with Santen. If the Company exercises this option, the Company will pay Santen a percentage of certain development expenses, and the Company will receive a percentage of profits from sales of the licensed products in the ophthalmology field in the United States, but will not also receive royalties on such sales. In consideration of the rights granted to Santen under the agreement, the Company received a one-time upfront fee of $10.0 million. In addition, the Company is eligible to receive up to a total of $155.0 million in milestone payments upon the achievement of certain milestones, of which $20.0 million relates to the initiation of certain development activities, $52.5 million relates to the submission of certain regulatory filings and receipt of certain regulatory approvals and $82.5 million relates to commercialization activities and the achievement of specified levels of product sales. As of March 31, 2019 and December 31, 2018, two development milestones had been received totaling $10.0 million. If carotuximab products are successfully commercialized in the field of ophthalmology, Santen will be required to pay the Company tiered royalties on net sales ranging from high single digits to low teens, depending on the volume of sales, subject to adjustments in certain circumstances. In addition, Santen will reimburse the Company for all royalties due by the Company under certain third party agreements with respect to the use, manufacture or commercialization of carotuximab products in the field of ophthalmology by Santen and its affiliates and sublicensees. Royalties will continue on a country-by-country basis through the later of the expiration of the Company’s patent rights applicable to the carotuximab products in a given country or 12 years after the first commercial sale of the first carotuximab product commercially launched in such country. Santen may unilaterally terminate this agreement in its entirety, or on a country-by-country basis, upon written notice to the Company. Either party may terminate the agreement in the event of the other party’s bankruptcy or dissolution or for the other party’s material breach of the agreement that remains uncured 90 days (or 30 days with respect to a payment breach) after receiving notice from the non-breaching party. Unless earlier terminated, the agreement continues in effect until the termination of Santen’s payment obligations. Upon the adoption of ASU 2014-09 on January 1, 2018, the Company assessed this agreement and identified multiple promised goods and services, which include at inception: (1) a license to patents, information and know-how related to carotuximab, (2) a technology transfer, and (3) a collaboration, including technical and regulatory support provided by the Company. In addition, customer options were identified that include manufacturing and supply obligations and shared chemistry, manufacturing and controls (CMC) development activities. All performance obligations were satisfied by the year ended December 31, 2017, which completed the Company’s obligations. Upon the adoption of ASC 2014-09 and as of March 31, 2019, the transaction price includes the $10.0 million upfront payment and the two development milestones received totaling $10.0 million, all of which had been fully recognized as revenue at December 31, 2017. The remaining $62.5 million of potential development and regulatory milestone payments are fully constrained as the achievement of the milestones is not considered probable, and therefore no amounts have been included in the transaction price for these remaining milestones. In addition, in accordance with ASU 2014-09, a ny consideration related to the commercialization and sales-based milestones (including royalties) will be recognized when the related sales occur and have also been excluded from the transaction price. The Company will re-evaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstances occur. Revenue recognized related to this agreement totaled $0 for the three months ended March 31, 2019 and 2018. Janssen In September 2016, the Company entered into a license and option agreement with Janssen (the License and Option Agreement) under which Janssen granted the Company a license to technology and intellectual property to develop, manufacture and commercialize two compounds: a small molecule inhibitor of androgen receptor and androgen receptor mutations (the AR Mutant Program or TRC253) which is intended for the treatment of men with prostate cancer, and an inhibitor of NF-kB inducing kinase (the NIK Program or TRC694). Following completion of the pre-clinical development of TRC694, the Company determined the compound did not warrant further development and, in February 2019, issued written notice to terminate the License and Option Agreement with respect to the NIK Program and returned TRC694 and all rights thereto to Janssen. With respect to the AR Mutant Program, the License and Option Agreement, as amended, provides Janssen with an option, which is exercisable until 90 days after the Company demonstrates clinical proof of concept of TRC253, to regain the rights to the licensed intellectual property and to obtain an exclusive license to commercialize the compounds and certain other specified intellectual property developed under the AR Mutant Program. If Janssen exercises the option, Janssen will be obligated to pay the Company (i) a one-time option exercise fee of $45.0 million; (ii) regulatory and commercial based milestone payments totaling up to $137.5 million upon achievement of specified events; and (iii) royalties in the low single digits on annual net sales of AR Mutant Program products. If Janssen does not exercise the option, the Company would then have the right to retain worldwide development and commercialization rights to the AR Mutant Program, in which case, the Company would be obligated to pay to Janssen (x) development and regulatory based milestone payments totaling up to $45.0 million upon achievement of specified events, and (y) royalties in the low single digits based on annual net sales of AR Mutant Program products, subject to certain specified reductions. No consideration was exchanged for these assets on the acquisition date. Given the early preclinical stage of development of these assets and the low likelihood of success of development through regulatory approval on the acquisition date, no value was assigned to these assets in the accompanying consolidated balance sheet. The Company is obligated to use diligent efforts to develop the AR Mutant Program according to agreed upon development plans, timelines and budgets. If the Company retains the AR Mutant Program, the Company is further obligated to use commercially reasonable efforts to develop, obtain marketing approval for, and commercialize licensed products. Until the expiration or earlier termination of the development term of the AR Mutant Program, under the License and Option Agreement, subject to specified exceptions, the Company has agreed not to research, develop or commercialize any compounds or products related to the AR Mutant Program, other than pursuant to the collaboration with Janssen. The License and Option Agreement may be terminated for uncured breach, bankruptcy, or the failure or inability to demonstrate clinical proof of concept with respect to a particular program during specified timeframes. In addition, the License and Option Agreement will automatically terminate with respect to the AR Mutant Program, upon Janssen exercising its option in respect of the AR Mutant Program and making payment of the option exercise fee to the Company or, if Janssen does not exercise the option, upon the expiration of all payment obligations of the Company to Janssen with respect of the AR Mutant Program. The Company may also terminate the License and Option Agreement in its entirety without cause, subject to specified conditions. Ambrx, Inc. In December 2017, the Company entered into a license agreement with Ambrx for the development and commercialization of the Company’s endoglin antibodies, including TRC105, in Greater China. The license granted Ambrx the exclusive rights to use, develop, manufacture and commercialize the Company’s endoglin antibodies in all indications (excluding ophthalmology which are held by Santen) in Greater China. In February 2019, following discussions between the Company and Ambrx regarding Ambrx’s progress towards initiating a Phase 1 clinical trial of TRC105 in China, Ambrx notified the Company that it had elected to terminate the license agreement, resulting in all rights to TRC105 in Greater China reverting to the Company. In consideration of the rights granted to Ambrx under the agreement, the Company received a one-time upfront fee of $3.0 million. In addition, the Company was eligible to receive up to a total of $140.5 million in milestone payments upon the achievement of certain milestones, of which $10.5 million related to the submission of certain regulatory filings and receipt of certain regulatory approvals and $130.0 million related to the achievement of specified levels of product sales. Ambrx was required to pay the Company tiered royalties on net sales ranging from high single digits to low teens, depending on the volume of sales, subject to adjustments in certain circumstances had TRC105 products been successfully commercialized in the territory. At December 31, 2017, the $3.0 million upfront payment had been received and was recorded as deferred revenue in the consolidated balance sheet. The license and know-how related to TRC105 was delivered to Ambrx in the first quarter of 2018, and accordingly, the $3.0 million was recognized as revenue in the first quarter of 2018. No further revenue will be recognized associated with this agreement given Ambrx’s decision to terminate the license agreement, resulting in all rights to TRC105 in Greater China reverting to the Company.

Leases

Leases	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Leases	7. Leases The Company leases its office space under a non‑cancelable operating lease that expires in April 2022 and may be extended for an additional term of 60 months. The option to extend this lease has been excluded from the lease term as the Company is not reasonably certain that the option will be exercised. The lease is subject to base lease payments and additional charges for common area maintenance and other costs and includes certain lease incentives and tenant improvement allowances. Operating lease expense was $0.1 million for the three months ended March 31, 2019 and 2018. As of March 31, 2019, the Company does not have any finance leases, nor any other operating leases. Supplemental cash flow information, as of March 31, 2019, related to operating leases was as follows (in thousands): Cash paid within operating cash flows $ 103 Right-of-use assets recognized in exchange for new lease obligations $ 1,143 Supplemental balance sheet information, as of March 31, 2019, related to operating leases was as follows (in thousands, except lease term and discount rate): Reported as: Other assets (ROU asset) $ 1,061 Accounts payable and accrued expenses (lease liability) $ 313 Other long-term liabilities (lease liability) 843 Total lease liabilities $ 1,156 Weighted average remaining lease term (in years) 3.0 Weighted average discount rate 11.3% As of March 31, 2019, the maturities of the Company’s operating lease liabilities are as follows (in thousands): Remaining 2019 $ 320 2020 442 2021 461 2022 156 Total lease payments 1,379 Less imputed interest (223) Total operating lease liabilities $ 1,156 Under the terms of the lease agreement, the Company provided the lessor with an irrevocable letter of credit in the amount of $175,000. The lessor is entitled to draw on the letter of credit in the event of any default by the Company under the terms of the lease. ASC 840 Disclosures The Company elected the alternative modified transition method and previously disclosed the following: Future minimum payments under the non‑cancelable operating lease as of December 31, 2018 were as follows (in thousands): 2019 $ 423 2020 442 2021 461 2022 156 $ 1,482

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	3 Months Ended
	Mar. 31, 2019
Organization And Accounting Policies [Abstract]
Organization and Business	Organization and Business TRACON Pharmaceuticals, Inc. (formerly Lexington Pharmaceuticals, Inc.) (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a clinical stage biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer and, through its license to Santen Pharmaceutical Co. Ltd. (Santen), wet age-related macular degeneration, or wet AMD. The Company’s product development platform, which emphasizes capital efficiency, also provides to ex-U.S. companies a rapid and capital-efficient U.S. drug development solution that includes U.S. and European Union (EU) clinical development expertise and U.S. commercialization expertise. The unaudited condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries, TRACON Pharma Limited and TRACON Pharma International Limited, which were formed in September 2015 and January 2019, respectively, and are currently inactive. All significant intercompany accounts and transactions have been eliminated.
Basis of Presentation	Basis of Presentation As of March 31, 2019, the Company has devoted substantially all of its efforts to product development, raising capital, and building infrastructure and has not realized revenues from its planned principal operations. The Company has incurred operating losses since inception. As of March 31, 2019, the Company had an accumulated deficit of $146.9 million. The Company anticipates that it will continue to incur net losses into the foreseeable future as it continues the development and commercialization of its product candidates and works to develop additional product candidates through research and development programs. At March 31, 2019, the Company had cash, cash equivalents, and short-term investments of $32.1 million. Based on the Company’s current business plan, management believes that there is substantial doubt as to whether existing cash, cash equivalents, and short-term investments will be sufficient to meet its obligations as they become due within one year from the date these financial statements are issued. The Company’s ability to execute its operating plan through 2020 and beyond depends on its ability to obtain additional funding through equity offerings, debt financings, or potential licensing and collaboration arrangements. The accompanying unaudited condensed consolidated financial statements have been prepared assuming the Company will continue as a going concern, which contemplates the realization of assets and settlement of liabilities in the normal course of business. However, the Company’s current working capital, anticipated operating expenses and net losses, and the uncertainties surrounding its ability to raise additional capital as needed, as discussed below, raise substantial doubt about its ability to continue as a going concern for a period of one year following the date that these financial statements are issued. The unaudited condensed consolidated financial statements do not include any adjustments for the recovery and classification of assets or the amounts and classification of liabilities that might be necessary should the Company be unable to continue as a going concern. The Company plans to continue to fund its losses from operations through cash, cash equivalents, and investments on hand, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements, including equity financing through the common stock purchase agreement the Company entered into with Aspire Capital Fund, LLC in March 2017 for the purchase of up to $21.0 million of the Company’s common stock over a 30 month period and/or the Capital on Demand TM Unaudited Interim Financial Information The unaudited condensed consolidated financial statements at March 31, 2019, and for the three months ended March 31, 2019 and 2018, have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC), and with accounting principles generally accepted in the United States (GAAP) applicable to interim financial statements. These unaudited condensed consolidated financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, consisting of only normal recurring accruals, which in the opinion of management are necessary to present fairly the Company’s financial position as of the interim date and results of operations for the interim periods presented. Interim results are not necessarily indicative of results for a full year or future periods. These unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2018, included in its Annual Report on Form 10-K filed with the SEC on March 1, 2019.
Use of Estimates	Use of Estimates The Company’s condensed consolidated financial statements are prepared in accordance with GAAP. The preparation of the Company’s condensed consolidated financial statements requires it to make estimates and assumptions that impact the reported amounts of assets, liabilities, revenue, and expenses. The most significant estimates in the Company’s financial statements relate to revenue recognition, expenses incurred for clinical trials, and the valuation of equity awards. Although these estimates are based on the Company’s knowledge of current events and actions it may undertake in the future, actual results may ultimately materially differ from these estimates and assumptions.
Cash and Cash Equivalents	Cash and Cash Equivalents Cash and cash equivalents consist of cash and highly liquid investments with original maturities of three months or less at the date of purchase. The carrying amounts approximate fair value due to the short maturities of these investments. Cash and cash equivalents include cash in readily available checking and money market funds.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to significant concentration of credit risk consist primarily of cash, cash equivalents, and investments. The Company maintains deposits in federally insured financial institutions in excess of federally insured limits. The Company has not experienced any losses in such accounts and management believes that the Company is not exposed to significant credit risk due to the financial position of the depository institutions in which those deposits are held.
Revenue Recognition	Revenue Recognition To date, substantially all of the Company’s revenue has been derived from its license agreements with Santen and Ambrx, Inc. (Ambrx) as described in Note 6. The terms of these arrangements include payments to the Company for the following: non-refundable, up-front license fees; development, regulatory and commercial milestone payments; payments for manufacturing supply services the Company provides through its contract manufacturers; and royalties on net sales of licensed products. In accordance with ASU 2014-09, the Company performs the following five steps in determining the appropriate amount of revenue to be recognized as it fulfills its obligations under each of these agreements: (i) identification of the contract(s) with a customer; (ii) determination of whether the promised goods or services are performance obligations including whether they are distinct in the context of the contract; (iii) measurement of the transaction price, including any constraint on variable consideration; (iv) allocation of the transaction price to the performance obligations; and (v) recognition of revenue when, or as, the Company satisfies each performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services transferred to the customer. Once a contract is determined to be within the scope of Accounting Standards Codification 606, Revenue from Contracts with Customers, at contract inception, the Company assesses the goods or services promised within the contract to determine those that are performance obligations and assesses whether each promised good is distinct. The Company then recognizes as revenue the amount of the transaction price that is allocated to the respective performance obligation when, or as, the performance obligation is satisfied. As part of the accounting for these arrangements, the Company develops assumptions that require judgment to determine the stand-alone selling price for each performance obligation identified in the contract. The Company uses key assumptions to determine the stand-alone selling price, which may include development timelines, reimbursement rates for personnel costs, discount rates, and probabilities of technical and regulatory success. Licenses of intellectual property: If the license to the Company’s intellectual property is determined to be distinct from the other performance obligations identified in the arrangement, the Company recognizes revenue allocated to the license when the license is transferred to the customer and the customer is able to use and benefit from the license. For licenses that are bundled with other promised goods or services, the Company utilizes judgment to assess the nature of the combined performance obligation to determine whether the combined performance obligation is satisfied over time or at a point in time and, if over time, the appropriate method of measuring progress for purposes of recognizing revenue. The Company evaluates the measure of progress each reporting period and, if necessary, adjusts the measure of performance and related revenue recognition. Milestone Payments: At the inception of each arrangement that includes development, commercialization, and regulatory milestone payments, the Company evaluates whether the achievement of the milestones is considered probable and estimates the amount to be included in the transaction price using the most likely amount method. Performance milestone payments represent a form of variable consideration. If it is probable that a significant revenue reversal would not occur, the associated milestone value is included in the transaction price. Achievement of milestones that are not within the control of the Company or the licensee, such as regulatory approvals, are not considered probable until the approvals are achieved. The transaction price is then allocated to each performance obligation on a relative stand-alone selling price basis and the Company recognizes revenue as or when the performance obligations under the contract are satisfied. At the end of each subsequent reporting period, the Company re-evaluates the probability of achieving such milestones and any related constraint, and if necessary, adjusts its estimate of the overall transaction price. Any such adjustments are recorded on a cumulative catch-up basis, which would affect revenues and earnings in the period of adjustment. Manufacturing Supply Services: Arrangements that include a promise for future supply of drug substance or drug product for either clinical development or commercial supply at the customer’s discretion are generally considered options. The Company assesses if these options provide a material right to the licensee and if so, they are accounted for as separate performance obligations at the outset of the arrangement. Royalties: For arrangements that include sales-based royalties, including milestone payments based on the level of sales, and the license is deemed to be the predominant item to which the royalties relate, the Company recognizes revenue at the later of (i) when the related sales occur or (ii) when the performance obligation to which some or all of the royalty has been allocated has been satisfied (or partially satisfied). To date, the Company has not recognized any royalty revenue resulting from any of its out-licensing arrangements. The Company receives payments from its collaborators based on billing schedules established in each contract. Up-front and other payments may require deferral of revenue recognition to a future period until the Company performs its obligations under its collaboration arrangements. Amounts are recorded as accounts receivable when the Company’s right to consideration is unconditional. The Company does not assess whether a contract has a significant financing component if the expectation at contract inception is such that the period between payment by the customer and the transfer of the promised goods or services to the customer will be one year or less.
Clinical Trial Expense Accruals	Clinical Trial Expense Accruals As part of the process of preparing the Company’s financial statements, the Company is required to estimate expenses resulting from its obligations under contracts with vendors, clinical sites, contract research organizations (CROs), and consultants in connection with conducting clinical trials. The financial terms of these contracts vary and may result in payment flows that do not match the periods over which materials or services are provided under such contracts. The Company’s objective is to reflect the appropriate trial expenses in its financial statements by recording those expenses in the period in which services are performed and efforts are expended. The Company accounts for these expenses according to the progress of the clinical trial as measured by patient progression and the timing of various aspects of the trial. The Company determines accrual estimates through discussion with the clinical sites and applicable personnel and outside service providers as to the progress or state of consummation of trials. During the course of a clinical trial, the Company adjusts the clinical expense recognition if actual results differ from its estimates. The Company makes estimates of accrued expenses as of each balance sheet date based on the facts and circumstances known at that time. The Company’s clinical trial accruals are dependent upon accurate reporting by clinical sites, CROs, and other third-party vendors. Although the Company does not expect its estimates to differ materially from amounts actually incurred, its understanding of the status and timing of services performed relative to the actual status and timing of services performed may vary and may result in reporting amounts that are too high or too low for any particular period. For the three months ended March 31, 2019 and 2018, there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of stock option grants, employee restricted stock unit grants (RSUs), and employee stock purchase plan (ESPP) rights recognized as expense over the requisite service period of the awards (usually the vesting period) on a straight-line basis. The Company estimates the fair value of stock option grants and ESPP rights using the Black-Scholes option pricing model. The fair value of RSUs is based on the stock price on the date of grant. Equity award forfeitures are recorded as they occur.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity during a period from transactions and other events and circumstances from non-owner sources. Net loss and comprehensive loss were the same for all periods presented.
Net Loss Per Share	Net Loss Per Share Basic net loss per share is calculated by dividing the net loss by the weighted-average shares of common stock outstanding for the period, without consideration for common stock equivalents and adjusted for the weighted average number of common shares outstanding that are subject to repurchase. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock method. 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. Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Three Months Ended March 31, 2019 2018 Warrants to purchase common stock 15,619,113 14,326,537 Common stock options and restricted stock units 4,509,499 3,111,882 ESPP shares — 8,579 20,128,612 17,446,998
Leases	Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are included in Other assets, Accounts payable and accrued expenses, and Other long-term liabilities within the consolidated balance sheet as of March 31, 2019. The Company currently does not have any finance leases. Operating lease right-of-use (ROU) assets and operating lease liabilities are recognized based on the present value of the future minimum lease payments over the lease term at commencement date. ROU assets also include any initial direct costs incurred and any lease payments made at or before the lease commencement date, less lease incentives received. The Company uses its incremental borrowing rate based on the information available at the commencement date in determining the lease liabilities as the Company’s leases generally do not provide an implicit rate. Lease terms may include options to extend or terminate when the Company is reasonably certain that the option will be exercised. Lease expense is recognized on a straight-line basis over the lease term.
Recently Adopted Accounting Standards	Recently Adopted Accounting Standards In February 2016, the FASB issued ASU 2016-02, Leases In June 2018, the FASB issued ASU 2018-07, Improvements to Nonemployee Share-Based Payment Accounting Compensation-Stock Compensation

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies (Tables)	3 Months Ended
	Mar. 31, 2019
Organization And Accounting Policies [Abstract]
Schedule of potentially dilutive securities not included in the calculation of diluted net loss per share	Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares): Three Months Ended March 31, 2019 2018 Warrants to purchase common stock 15,619,113 14,326,537 Common stock options and restricted stock units 4,509,499 3,111,882 ESPP shares — 8,579 20,128,612 17,446,998

Short-Term Investments, Cash _2

Short-Term Investments, Cash Equivalents and Fair Value Measurements (Tables)	3 Months Ended
	Mar. 31, 2019
Fair Value Disclosures [Abstract]
Schedule of Available-for-sale Securities	Cash equivalents, which are classified as equity securities, and short-term investments, which are classified as available-for-sale securities, consisted of the following (in thousands): March 31, 2019 December 31, 2018 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 900 $ — $ — $ 900 $ 5,832 $ — $ — $ 5,832 U.S. treasury securities 13,982 — — 13,982 13,968 — — 13,968 $ 14,882 $ — $ — $ 14,882 $ 19,800 $ — $ — $ 19,800 Classified as: Cash equivalents $ 4,898 $ 5,832 Short-term investments 9,984 13,968 Total Cash equivalents and Short-term investments $ 14,882 $ 19,800
Schedule of assets and liabilities measured at fair value on a recurring basis	The fair values of the Company’s assets and liabilities, which are measured at fair value on a recurring basis, were determined using the following inputs (in thousands): Fair Value Measurements at Reporting Date Using Quoted Prices in Significant Active Markets Other Significant for Identical Observable Unobservable Assets Inputs Inputs Total (Level 1) (Level 2) (Level 3) At March 31, 2019 Money market funds and U.S. treasury securities, included in Cash equivalents and Short-term investments $ 14,882 $ — $ 14,882 $ — At December 31, 2018 Money market funds and U.S. treasury securities, included in Cash equivalents and Short-term investments $ 19,800 $ — $ 19,800 $ —

Long-Term Debt (Tables)

Long-Term Debt (Tables)	3 Months Ended
	Mar. 31, 2019
Debt Disclosure [Abstract]
Schedule of Long-term debt and unamortized debt discount balances	Long-term debt and unamortized debt discount balances were as follows (in thousands): March 31, December 31, 2019 2018 Long-term debt $ 7,000 $ 7,000 Less debt discount, net of current portion (196) (257) Long-term debt, net of debt discount 6,804 6,743 Less current portion of long-term debt (2,100) (1,400) Long-term debt, net of current portion $ 4,704 $ 5,343 Current portion of long-term debt $ 2,100 $ 1,400 Current portion of debt discount (294) (316) Current portion of long-term debt, net $ 1,806 $ 1,084
Schedule of exercisable outstanding warrants for purchase of common stock issued	At March 31, 2019, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 May 25, 2025 53,639 $ 2.61 157,504 As of March 31, 2019 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 March 27, 2024 13,696,067 $ 2.70 March 27, 2025 1,765,542 $ 0.01 May 3, 2025 53,639 $ 2.61 15,619,113
Schedule of future minimum principal and interest payments	Future minimum principal and interest payments under the 2018 Amended SVB Loan, including the final payment, are as follows (in thousands): Remaining 2019 1,855 2020 3,195 2021 3,218 8,268 Less interest and final payment (1,268) Long-term debt $ 7,000

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	3 Months Ended
	Mar. 31, 2019
Stockholders Equity Note [Abstract]
Schedule of Changes in Stockholders' Equity	The following tables present the changes in stockholders’ equity (in thousands, except share data): Three Months Ended March 31, 2019 Additional Total Common Stock Paid-in Accumulated Stockholders’ Shares Amount Capital Deficit Equity Balance at December 31, 2018 29,871,327 $ 30 $ 161,072 $ (139,660 ) $ 21,442 Issuance of common stock under equity plans 27,371 — (20 ) — (20) Stock-based compensation expense — — 596 — 596 Net loss — — — (7,213 ) (7,213) Balance at March 31, 2019 29,898,698 $ 30 $ 161,648 $ (146,873 ) $ 14,805 Three Months Ended March 31, 2018 Additional Total Common Stock Paid-in Accumulated Stockholders’ Shares Amount Capital Deficit Equity Balance at December 31, 2017 17,711,928 $ 18 $ 121,670 $ (104,701 ) $ 16,987 Issuance of common stock under equity plans 38,019 — (78 ) — (78) Stock-based compensation expense — — 706 — 706 Vested shares related to repurchase liability — — 3 — 3 Issuances of common stock and warrants, net of offering costs 10,691,588 10 33,225 — 33,235 Net loss — — — (8,364 ) (8,364) Balance at March 31, 2018 28,441,535 $ 28 $ 155,526 $ (113,065 ) $ 42,489
Schedule of exercisable outstanding warrants for purchase of common stock issued	At March 31, 2019, the Company had the following exercisable outstanding warrants for the purchase of common stock issued in connection with the Company’s loan agreements with SVB: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 May 25, 2025 53,639 $ 2.61 157,504 As of March 31, 2019 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 18,415 $ 10.86 November 14, 2023 through June 4, 2024 38,758 $ 7.74 January 25, 2024 46,692 $ 5.14 March 27, 2024 13,696,067 $ 2.70 March 27, 2025 1,765,542 $ 0.01 May 3, 2025 53,639 $ 2.61 15,619,113
Summary of weighted-average assumptions used Black-Scholes option pricing model to determine the fair value	The weighted-average 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, 2019 2018 Risk-free interest rate 2.6 % 2.8% Expected volatility 81 % 79% Expected term (in years) 6.3 6.3 Expected dividend yield — % —%
Summary of allocation of stock-based compensation expense	The allocation of stock-based compensation expense was as follows (in thousands): Three Months Ended March 31, 2019 2018 Research and development $ 316 $ 364 General and administrative 280 342 $ 596 $ 706

Leases (Tables)

Leases (Tables)	3 Months Ended
	Mar. 31, 2019
Leases [Abstract]
Schedule of supplemental cash flow information related to operating leases	Supplemental cash flow information, as of March 31, 2019, related to operating leases was as follows (in thousands): Cash paid within operating cash flows $ 103 Right-of-use assets recognized in exchange for new lease obligations $ 1,143
Schedule of supplemental balance sheet information related to operating leases	Supplemental balance sheet information, as of March 31, 2019, related to operating leases was as follows (in thousands, except lease term and discount rate): Reported as: Other assets (ROU asset) $ 1,061 Accounts payable and accrued expenses (lease liability) $ 313 Other long-term liabilities (lease liability) 843 Total lease liabilities $ 1,156 Weighted average remaining lease term (in years) 3.0 Weighted average discount rate 11.3%
Schedule of maturities of operating lease liabilities	As of March 31, 2019, the maturities of the Company’s operating lease liabilities are as follows (in thousands): Remaining 2019 $ 320 2020 442 2021 461 2022 156 Total lease payments 1,379 Less imputed interest (223) Total operating lease liabilities $ 1,156
Schedule of future minimum payments under non-cancelable operating lease	Future minimum payments under the non‑cancelable operating lease as of December 31, 2018 were as follows (in thousands): 2019 $ 423 2020 442 2021 461 2022 156 $ 1,482

Organization and Summary of S_4

Organization and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($)	1 Months Ended
	Mar. 31, 2017	Mar. 31, 2019	Feb. 28, 2019	Dec. 31, 2018
Basis of Presentation
Accumulated deficit		$ (146,873,000)		$ (139,660,000)
Cash, cash equivalents and short-term investments		$ 32,100,000
Jones Trading Institutional Services LLC | Capital on Demand Sales Agreement | Common Stock
Basis of Presentation
Maximum aggregate value of stock to be sold			$ 8,000,000
Aspire Capital | Common Stock
Basis of Presentation
Maximum aggregate value of common stock to be purchase	$ 21,000,000
Sale duration for common stock under purchase agreement	30 months

Organization and Summary of S_5

Organization and Summary of Significant Accounting Policies - Schedule of Potentially Dilutive Securities Not Included in the Calculation of Diluted Net Loss Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	20,128,612	17,446,998
Warrants to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	15,619,113	14,326,537
Common Stock Options and Restricted Stock Units
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities	4,509,499	3,111,882
ESPP Shares
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities		8,579

Short-Term Investments, Cash _3

Short-Term Investments, Cash Equivalents and Fair Value Measurements - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019USD ($)
Fair Value Disclosures [Abstract]
Maximum period for remaining contractual maturities of available-for-sale investments	1 year
Amount of transfers between levels	$ 0

Short-Term Investments, Cash _4

Short-Term Investments, Cash Equivalents and Fair Value Measurements - Schedule of Available for Sale Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	$ 14,882	$ 19,800
Estimated Fair Value	14,882	19,800
Short-term investments	9,984	13,968
Estimated Fair Value
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cash equivalents	4,898	5,832
Short-term investments	9,984	13,968
Money market funds
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	900	5,832
Estimated Fair Value	900	5,832
U.S. treasury securities
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	13,982	13,968
Estimated Fair Value	$ 13,982	$ 13,968

Short-Term Investments, Cash _5

Short-Term Investments, Cash Equivalents and Fair Value Measurements - Schedule of Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - Recurring - Money market funds and U.S. treasury securities, included in Cash equivalents and Short-term investments - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Assets:
Fair value, assets	$ 14,882	$ 19,800
Level 2
Assets:
Fair value, assets	$ 14,882	$ 19,800

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt and Unamortized Debt Discount Balances (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Long-term debt
Long-term debt	$ 7,000	$ 7,000
Less debt discount, net of current portion	(196)	(257)
Long-term debt, net of debt discount	6,804	6,743
Less current portion of long-term debt	(2,100)	(1,400)
Long-term debt, net of current portion	4,704	5,343
Current portion of long-term debt	2,100	1,400
Current portion of debt discount	(294)	(316)
Current portion of long-term debt, net	$ 1,806	$ 1,084

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details) - USD ($)	1 Months Ended
	May 31, 2018	Mar. 31, 2019
Debt Instrument [Line Items]
Warrants issued		15,619,113
Silicon Valley Bank
Debt Instrument [Line Items]
Warrants issued		157,504
2018 SVB Loan | Silicon Valley Bank
Debt Instrument [Line Items]
Proceeds from long-term debt	$ 7,000,000
Interest rate	9.00%
Repayment period	30 months
Additional fee on final payment due (as a percent)	4.00%
Warrants issued	53,639
Exercise price (per share)	$ 2.61
2018 SVB Loan | Silicon Valley Bank | After May 3, 2018 Prior to May 3, 2020
Debt Instrument [Line Items]
Prepayment fee (as a percent)	2.00%
2018 SVB Loan | Silicon Valley Bank | After May 3, 2020
Debt Instrument [Line Items]
Prepayment fee (as a percent)	1.00%
2017 SVB Loan | Silicon Valley Bank
Debt Instrument [Line Items]
Final payment on payoff	$ 300,000

Long-Term Debt - Schedule of Ex

Long-Term Debt - Schedule of Exercisable Outstanding Warrants for Purchase of Common Stock Issued (Details)	Mar. 31, 2019$ / sharesshares
Debt Instrument [Line Items]
Warrants issued	15,619,113
Silicon Valley Bank
Debt Instrument [Line Items]
Warrants issued	157,504
Silicon Valley Bank | May 13, 2022
Debt Instrument [Line Items]
Warrants issued	18,415
Exercise price (per share) | $ / shares	$ 10.86
Silicon Valley Bank | November 14, 2023 Through June 4, 2024
Debt Instrument [Line Items]
Warrants issued	38,758
Exercise price (per share) | $ / shares	$ 7.74
Silicon Valley Bank | January 25, 2024
Debt Instrument [Line Items]
Warrants issued	46,692
Exercise price (per share) | $ / shares	$ 5.14
Silicon Valley Bank | May 25, 2025
Debt Instrument [Line Items]
Warrants issued	53,639
Exercise price (per share) | $ / shares	$ 2.61

Long-Term Debt - Schedule of Fu

Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 7,000	$ 7,000
2018 SVB Loan
Debt Instrument [Line Items]
Remaining 2019	1,855
2020	3,195
2021	3,218
Long-term debt including final payment	8,268
Less interest and final payment	(1,268)
Long-term debt	$ 7,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	Mar. 31, 2019USD ($)
Commitments and Contingencies
Estimated non-cancelable purchase obligations	$ 1.1
Research and development arrangement
Commitments and Contingencies
Potential milestone payable	$ 66

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Changes in Stockholders' Equity (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class Of Stock [Line Items]
Balance at December 31, 2018	$ 21,442	$ 16,987
Issuance of common stock under equity plans	(20)	(78)
Stock-based compensation expense	596	706
Vested shares related to repurchase liability		3
Issuances of common stock and warrants, net of offering costs		33,235
Net loss	(7,213)	(8,364)
Balance at March 31, 2019	14,805	42,489
Common Stock
Class Of Stock [Line Items]
Balance at December 31, 2018	$ 30	$ 18
Balance (in Shares)	29,871,327	17,711,928
Issuance of common stock under equity plans (in shares)	27,371	38,019
Issuances of common stock and warrants, net of offering costs		$ 10
Issuances of Common Stock and Warrants Net of Offering Costs (in shares)		10,691,588
Balance at March 31, 2019	$ 30	$ 28
Balance (in Shares)	29,898,698	28,441,535
Additional Paid-in Capital
Class Of Stock [Line Items]
Balance at December 31, 2018	$ 161,072	$ 121,670
Issuance of common stock under equity plans	(20)	(78)
Stock-based compensation expense	596	706
Vested shares related to repurchase liability		3
Issuances of common stock and warrants, net of offering costs		33,225
Balance at March 31, 2019	161,648	155,526
Accumulated Deficit
Class Of Stock [Line Items]
Balance at December 31, 2018	(139,660)	(104,701)
Net loss	(7,213)	(8,364)
Balance at March 31, 2019	$ (146,873)	$ (113,065)

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended			3 Months Ended	12 Months Ended
	Sep. 30, 2018	Apr. 30, 2018	Mar. 31, 2018	Mar. 31, 2019	Dec. 31, 2018	Feb. 28, 2019
Class Of Stock [Line Items]
Conversion of warrants to purchase shares				15,619,113
Warrants exercised				0	0
Angel Pond Capital
Class Of Stock [Line Items]
Related party transaction, description of transaction				Company paid Angel Pond Capital, an affiliate of a holder of more than 5% of the Company’s common stock and an affiliate of a member of the Company’s Board of the Directors, a fee totaling approximately $1.9 million as consideration for acting as a nonexclusive placement agent for this financing
Payment of placement agent fee		$ 1,900,000
Pre-Funded Warrants and Common Warrants
Class Of Stock [Line Items]
Maximum percentage of holders ownership interest in common stock to exercise warrants.		9.99%	9.99%
Maximum percentage of holders ownership interest in common stock after exercise		19.99%	19.99%
Common Stock | Equity Plan Activity
Class Of Stock [Line Items]
Shares issued upon exercise of outstanding stock options				0	136,720
Common Stock | Equity Plan Activity | Restricted Stock Units
Class Of Stock [Line Items]
Shares withheld on vesting date to settle employees minimum statutory tax obligations				18,934
Shares issued upon vesting of restricted stock units				27,371	38,019
Private Placement | Common Stock
Class Of Stock [Line Items]
Stock issued during period, shares, new issues		11,930,525	11,930,525
Shares issued, price per share		$ 2.70	$ 2.70
Net proceeds received in private placement		$ 36,500,000	$ 36,500,000
Private Placement | Common Stock | Pre-Funded Warrants
Class Of Stock [Line Items]
Shares issued, price per share		$ 2.69	$ 2.69
Conversion of warrants to purchase shares		1,765,542	1,765,542
Exercise price (per share)		$ 0.01	$ 0.01
Private Placement | Common Stock | Common Warrants
Class Of Stock [Line Items]
Shares issued, price per share		$ 0.125	$ 0.125
Conversion of warrants to purchase shares		13,696,067	13,696,067
Exercise price (per share)		$ 2.70	$ 2.70
Capital on Demand Sales Agreement | Common Stock | Jones Trading Institutional Services LLC
Class Of Stock [Line Items]
Maximum aggregate value of stock to be sold						$ 8,000,000
Capital on Demand Sales Agreement | Aspire Capital | Jones Trading Institutional Services LLC
Class Of Stock [Line Items]
Stock issued during period, shares, new issues				0
Maximum aggregate value of stock to be sold	$ 8,000,000
Percentage of gross proceeds, required to pay for common stock sold through sales agreement	2.50%
Common stock remains available for sale	$ 8,000,000
At The Market Equity Offering Sales Agreement | Aspire Capital | Stifel Nicolaus And Company Incorporated
Class Of Stock [Line Items]
Stock issued during period, value, new issues	$ 3,500,000

Stockholders' Equity - Schedu_2

Stockholders' Equity - Schedule of Outstanding Warrants for Purchase of Common Stock Issued (Details)	Mar. 31, 2019$ / sharesshares
Class Of Stock [Line Items]
Warrants issued	15,619,113
May 13, 2022
Class Of Stock [Line Items]
Warrants issued	18,415
Exercise price (per share) | $ / shares	$ 10.86
November 14, 2023 Through June 4, 2024
Class Of Stock [Line Items]
Warrants issued	38,758
Exercise price (per share) | $ / shares	$ 7.74
January 25, 2024
Class Of Stock [Line Items]
Warrants issued	46,692
Exercise price (per share) | $ / shares	$ 5.14
March 27, 2024
Class Of Stock [Line Items]
Warrants issued	13,696,067
Exercise price (per share) | $ / shares	$ 2.70
March 27, 2025
Class Of Stock [Line Items]
Warrants issued	1,765,542
Exercise price (per share) | $ / shares	$ 0.01
May 3, 2025
Class Of Stock [Line Items]
Warrants issued	53,639
Exercise price (per share) | $ / shares	$ 2.61

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Weighted-Average Assumptions Fair Value of the Employee Stock Option Grants (Details) - Stock Option	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class Of Stock [Line Items]
Risk-free interest rate	2.60%	2.80%
Expected volatility	81.00%	79.00%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days
Expected dividend yield	0.00%	0.00%

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Allocation of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018
Class Of Stock [Line Items]
Stock based compensation expense	$ 596	$ 706
Research and development
Class Of Stock [Line Items]
Stock based compensation expense	316	364
General and administrative
Class Of Stock [Line Items]
Stock based compensation expense	$ 280	$ 342

Collaborations - Additional Inf

Collaborations - Additional Information (Details)	1 Months Ended			3 Months Ended		12 Months Ended
	Feb. 28, 2019USD ($)	Nov. 30, 2018USD ($)antibody	Mar. 31, 2014USD ($)	Mar. 31, 2019USD ($)Milestone	Mar. 31, 2018USD ($)	Dec. 31, 2018USD ($)	Dec. 31, 2017USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contracts Revenue				$ 0	$ 3,000,000
Type of Revenue [Extensible List]				tcon:CollaborationMember	tcon:CollaborationMember
TJ4309 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of cost bearing		40.00%
I-Mab | Bispecific Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum number of proprietary bispecific antibodies under development | antibody		5
Number of biological targets | antibody		2
I-Mab | Bispecific Agreement | North America
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum period of selecting candidates for development and commercialization		5 years
I-Mab | Bispecific Agreement | Before IND
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One time upfront payment fee		$ 10,000,000
Development and regulatory based on milestone payments		90,000,000
Potential milestones payments received		250,000,000
I-Mab | Bispecific Agreement | After IND Before Phase 1a
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One time upfront payment fee		25,000,000
Development and regulatory based on milestone payments		125,000,000
Potential milestones payments received		250,000,000
I-Mab | Bispecific Agreement | After Phase 1a and Before Phase 2
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One time upfront payment fee		50,000,000
Development and regulatory based on milestone payments		250,000,000
Potential milestones payments received		250,000,000
I-Mab | Bispecific Agreement | After Phase 2
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One time upfront payment fee		80,000,000
Development and regulatory based on milestone payments		420,000,000
Potential milestones payments received		$ 250,000,000
I-Mab | Collaboration Agreements
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Consideration exchanged for assets acquired				$ 0
Value given to assets acquired				$ 0
I-Mab | TJ4309 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of cost bearing		60.00%
Termination of agreement upon completion of clinical study		90 days
Additional payment		$ 35,000,000
I-Mab | TJ4309 Agreement | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-royalty consideration		35,000,000
I-Mab | TJ4309 Agreement | First Phase Clinical Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination fee		9,000,000
I-Mab | TJ4309 Agreement | First Phase Two Clinical Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination fee		$ 15,000,000
Santen | Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One-time upfront fee			$ 10,000,000
Potential milestone that could be received			155,000,000
Royalty continuation term				12 years
Cure period for bankruptcy or dissolution				90 days
Cure period for breach of payment				30 days
Contracts Revenue				$ 0	$ 0
Type of Revenue [Extensible List]				tcon:CollaborationArrangementMember	tcon:CollaborationArrangementMember
Santen | Collaborative Arrangement | Accounting Standards Update (ASU) No. 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments recognized as revenue				$ 0			$ 10,000,000
Santen | Collaborative Arrangement | Development Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone that could be received			20,000,000
Number of milestone payments received | Milestone				2
Potential milestones payments received				$ 10,000,000		$ 10,000,000
Santen | Collaborative Arrangement | Development Milestones | Accounting Standards Update (ASU) No. 2014-09
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Milestone payments recognized as revenue							$ 10,000,000
Santen | Collaborative Arrangement | Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone that could be received			52,500,000
Santen | Collaborative Arrangement | Commercialization Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone that could be received			$ 82,500,000
Santen | Collaborative Arrangement | Development And Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Balance of potential milestone that could be received				$ 62,500,000
Janssen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License and Option Agreement termination description				The License and Option Agreement may be terminated for uncured breach, bankruptcy, or the failure or inability to demonstrate clinical proof of concept with respect to a particular program during specified timeframes. In addition, the License and Option Agreement will automatically terminate with respect to the AR Mutant Program, upon Janssen exercising its option in respect of the AR Mutant Program and making payment of the option exercise fee to the Company or, if Janssen does not exercise the option, upon the expiration of all payment obligations of the Company to Janssen with respect of the AR Mutant Program. The Company may also terminate the License and Option Agreement in its entirety without cause, subject to specified conditions.
Janssen | License and Option Agreement | AR Mutant Program
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Development and regulatory based on milestone payments				$ 45,000,000
Exercisable period				90 days
License and option agreement terms				Janssen will be obligated to pay the Company (i) a one-time option exercise fee of $45.0 million; (ii) regulatory and commercial based milestone payments totaling up to $137.5 million upon achievement of specified events; and (iii) royalties in the low single digits on annual net sales of AR Mutant Program products.
One-time option exercise fee				$ 45,000,000
Regulatory and commercial based milestone payments				137,500,000
Janssen | License and Option Agreement | NIK Program
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Consideration exchanged for assets acquired				0
Value given to assets acquired				$ 0
Ambrx Inc | Collaborative Arrangement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
One-time upfront fee	$ 3,000,000
Potential milestone that could be received	140,500,000
Ambrx Inc | Collaborative Arrangement | Regulatory Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone that could be received	10,500,000
Ambrx Inc | Collaborative Arrangement | Product Sales Milestones
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential milestone that could be received	$ 130,000,000

Leases - Additional Information

Leases - Additional Information (Details)	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Non-cancelable operating lease expiration term	2022-04
Non-cancelable operating lease additional term to be extended	60 months
Operating lease expense	$ 100,000
Finance lease liability	0
Operating lease liability	0
Irrevocable letter of credit provided to lessor	$ 175,000

Leases - Supplemental cash flow

Leases - Supplemental cash flow information related to operating leases (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019USD ($)
Leases [Abstract]
Cash paid within operating cash flows	$ 103
Right-of-use assets recognized in exchange for new lease obligations	$ 1,143

Leases - Supplemental balance s

Leases - Supplemental balance sheet information related to operating leases (Details) $ in Thousands	Mar. 31, 2019USD ($)
Reported as:
Total lease liabilities	$ 1,156
Weighted average remaining lease term (in years)	3 years
Weighted average discount rate	11.30%
Other assets (ROU asset)
Reported as:
Other assets (ROU asset)	$ 1,061
Accounts payable and accrued expenses (lease liability)
Reported as:
Total lease liabilities	313
Other long-term liabilities (lease liability)
Reported as:
Total lease liabilities	$ 843

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Future minimum payments under non-cancelable operating lease
Remaining 2019	$ 320
2020	442	$ 442
2021	461	461
2022	156	$ 156
Total lease payments	1,379
Less imputed interest	(223)
Total operating lease liabilities	$ 1,156

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Payments Under the Non-Cancelable Operating Lease (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Future minimum payments under non-cancelable operating lease
2019		$ 423
2020	$ 442	442
2021	461	461
2022	$ 156	156
Total		$ 1,482