TRACON Pharmaceuticals (TCON) 10-K 25 Feb 21 2020 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Feb. 19, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
Entity Registrant Name	TRACON Pharmaceuticals, Inc.
Entity Central Index Key	0001394319
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Well-known Seasoned Issuer	No
Entity Public Float			$ 14.3
Entity Common Stock, Shares Outstanding		15,478,787
Entity Shell Company	false
Entity Small Business	true
Entity Emerging Growth Company	false
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	TCON
Security Exchange Name	NASDAQ
Entity File Number	001-36818
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	34-2037594
Entity Address, Address Line One	4350 La Jolla Village Drive
Entity Address, Address Line Two	Suite 800
Entity Address, City or Town	San Diego
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92122
City Area Code	858
Local Phone Number	550-0780
Document Annual Report	true
Document Transition Report	false
ICFR Auditor Attestation Flag	false
Documents Incorporated by Reference	DOCUMENTS INCORPORATED BY REFERENCE Portions of the registrant’s definitive proxy statement to be filed with the Securities and Exchange Commission (SEC) subsequent to the date hereof pursuant to Regulation 14A in connection with the Registrant’s 2021 Annual Meeting of Stockholders, are incorporated by reference into Part III of this Annual Report on Form 10-K. Such proxy statement will be filed with the SEC not later than 120 days after the conclusion of the registrant's fiscal year ended December 31, 2020.

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 32,131	$ 16,412
Short-term investments	3,999	0
Prepaid and other assets	784	848
Total current assets	36,914	17,260
Property and equipment, net	16	23
Other assets	508	838
Total assets	37,438	18,121
Current liabilities:
Accounts payable and accrued expenses	6,235	7,875
Accrued compensation and related expenses	1,590	1,355
Long-term debt, current portion	2,718	2,604
Total current liabilities	10,543	11,834
Other long-term liabilities	432	850
Long-term debt, less current portion	1,391	2,739
Commitments and contingencies (Note 5)
Stockholders’ equity:
Preferred stock, $0.001 par value, authorized shares — 10,000,000 at December 31, 2020 and December 31, 2019; issued and outstanding shares — none
Common stock, $0.001 par value; authorized shares — 40,000,000 and 20,000,000 at December 31, 2020 and December 31, 2019, respectively; issued and outstanding shares — 15,478,787 and 4,051,187 at December 31, 2020 and December 31, 2019, respectively	15	4
Additional paid-in capital	204,166	165,028
Accumulated deficit	(179,109)	(162,334)
Total stockholders’ equity	25,072	2,698
Total liabilities and stockholders’ equity	$ 37,438	$ 18,121

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - $ / shares	Dec. 31, 2020	Dec. 31, 2019
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	40,000,000	20,000,000
Common stock, shares issued	15,478,787	15,478,787
Common stock, shares outstanding	4,051,187	4,051,187

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Statement [Abstract]
Collaboration revenue	$ 0	$ 0	$ 3,000
Type of Revenue [Extensible List]	tcon:CollaborationMember	tcon:CollaborationMember	tcon:CollaborationMember
Operating expenses:
Research and development	$ 8,198	$ 14,530	$ 30,460
General and administrative	8,025	7,766	7,280
Total operating expenses	16,223	22,296	37,740
Loss from operations	(16,223)	(22,296)	(34,740)
Other income (expense):
Interest expense, net	(545)	(386)	(231)
Other income (expense), net	(7)	8	12
Total other expense	(552)	(378)	(219)
Net loss	$ (16,775)	$ (22,674)	$ (34,959)
Net loss per share, basic and diluted	$ (1.87)	$ (7.47)	$ (12.97)
Weighted-average shares outstanding, basic and diluted	8,984,148	3,034,299	2,694,624

Consolidated Statements of Stoc

Consolidated Statements of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Balance at Dec. 31, 2017	$ 16,987	$ 2	$ 121,686	$ (104,701)
Balance (in Shares) at Dec. 31, 2017		1,771,242
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	185		185
Issuance of common stock under equity plans (in shares)		22,881
Stock-based compensation expense	2,667		2,667
Vested shares related to repurchase liability	8		8
Issuances of common stock and warrants, net of offering costs	36,456	$ 1	36,455
Issuances of Common Stock and Warrants Net of Offering Costs (in shares)		1,193,059
Issuance of common stock warrants in connection with debt financing	98		98
Net loss	(34,959)			(34,959)
Balance at Dec. 31, 2018	21,442	$ 3	161,099	(139,660)
Balance (in Shares) at Dec. 31, 2018		2,987,182
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	12		12
Issuance of common stock under equity plans (in shares)		9,270
Stock-based compensation expense	1,624		1,624
Issuances of common stock, net of offering costs	2,294	$ 1	2,293
Issuances of common stock, net of offering costs (in shares)		1,054,735
Net loss	(22,674)			(22,674)
Balance at Dec. 31, 2019	2,698	$ 4	165,028	(162,334)
Balance (in Shares) at Dec. 31, 2019		4,051,187
Increase (Decrease) in Shareholders' Equity
Issuance of common stock under equity plans	2		2
Issuance of common stock under equity plans (in shares)		6,628
Stock-based compensation expense	1,034		1,034
Issuances of common stock and warrants, net of offering costs	37,987	$ 11	37,976
Issuances of Common Stock and Warrants Net of Offering Costs (in shares)		11,320,972
Issuance of common stock in exchange for services	126		126
Issuance of common stock in exchange for services (in shares)		100,000
Net loss	(16,775)			(16,775)
Balance at Dec. 31, 2020	$ 25,072	$ 15	$ 204,166	$ (179,109)
Balance (in Shares) at Dec. 31, 2020		15,478,787

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Cash flows from operating activities
Net loss	$ (16,775)	$ (22,674)	$ (34,959)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	1,034	1,624	2,667
Common stock issued for services	126
Depreciation and amortization	12	22	28
Noncash interest	123	234	272
Amortization of debt discount	43	81	94
Amortization of premium/discount on short-term investments	(1)	(52)	(100)
Lease asset amortization and liability accretion, net	(25)	(6)
Deferred rent			11
Deferred revenue			(3,000)
Changes in assets and liabilities:
Prepaid expenses and other assets	64	651	92
Accounts payable and accrued expenses	(1,878)	(3,421)	4,142
Accrued compensation and related expenses	235	(109)	(30)
Net cash used in operating activities	(17,042)	(23,650)	(30,783)
Cash flows from investing activities
Purchase of property and equipment	(5)
Purchases of available-for-sale short-term investments	(3,998)	(4,980)	(32,869)
Proceeds from the maturity of available-for-sale short-term investments		19,000	24,000
Net cash provided by (used in) investing activities	(4,003)	14,020	(8,869)
Cash flows from financing activities
Proceeds from long-term debt			7,000
Repayment of long-term debt	(1,400)	(1,400)	(8,320)
Proceeds from sale of common stock and warrants, net of offering costs	38,162	2,294	36,456
Proceeds from issuance of common stock under equity plans, net of tax withholdings	2	12	185
Net cash provided by financing activities	36,764	906	35,321
Increase (decrease) in cash and cash equivalents	15,719	(8,724)	(4,331)
Cash and cash equivalents at beginning of period	16,412	25,136	29,467
Cash and cash equivalents at end of period	32,131	16,412	25,136
Supplemental disclosure of cash flow information
Interest paid	$ 443	612	642
Supplemental schedule of noncash investing and financing activities
Issuance of common stock warrants in connection with long-term debt			$ 98
Issuance of common stock in connection with common stock purchase agreement		$ 450

Organization and Summary of Sig

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2020
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. (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer, and utilizes its cost efficient, contract research organization (CRO) independent product development platform to partner with ex-U.S. companies to develop and commercialize innovative products in the United States. The 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 December 31, 2020, 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 December 31, 2020, the Company had an accumulated deficit of $179.1 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 December 31, 2020, the Company had cash, cash equivalents, and short-term investments of $36.1 million. Based on the Company’s current business plan, management believes that existing cash, cash equivalents, and short-term investments will be sufficient to fund the Company’s obligations for a period in excess of one year from the date of issuance of these financial statements. The completion of the two registered direct offerings in December 2020, which generated net proceeds of $13.6 million, the completion of the private placement of the Company’s common stock and pre-funded warrants in August 2020, which generated net proceeds to the Company of $10.0 million, the sale of the Company’s common stock under the common stock purchase agreement with Aspire Capital Fund, LLC (Aspire Capital), which generated net proceeds of $9.6 million during 2020, and the sale of the Company’s common stock under its prior Capital on Demand™ sales agreement with JonesTrading Institutional Services LLC (JonesTrading), which generated net proceeds of $4.8 million during 2020, alleviated the substantial doubt about the Company’s ability to continue as a going concern which existed at the reporting date of the December 31, 2019 consolidated financial statements. The Company plans to continue to fund its losses from operations through its existing cash, cash equivalents, and short-term investments, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Aspire Capital in October 2019, as amended in April 2020, for the purchase of up to $15.0 million of the Company’s common stock over the 30 month period of the purchase agreement, $5.4 million of which remained available for sale , TM Risks and Uncertainties In December 2019, COVID-19, a novel strain of coronavirus, was first reported in Wuhan, China and has since become a global pandemic. The virus continues to spread globally, has been declared a pandemic by the World Health Organization and has spread to over The Company has experienced temporary closures of its offices in light of state and local orders and most of its employees continue to work remotely. In addition, the Company’s employees have not been able to conduct normal business travel, in particular as part of business development activities or in-person monitoring of clinical trial sites. Potential further impacts to the Company’s business include, but are not limited to, additional closures of its facilities or those of its vendors, continued disruptions or restrictions on its employees’ ability to travel, disruptions to or delays in ongoing clinical trials, third-party manufacturing supply and other operations, the potential diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, interruptions or delays in the operations of the U.S. Food and Drug Administration or other regulatory authorities, and the Company’s ability to raise capital and conduct business development activities. Use of Estimates The Company’s consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP). The preparation of the Company’s 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 expenses incurred for clinical trials. 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. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company's assets or liabilities as of the date of this filing. 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 and cash equivalents. 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. Property and Equipment Property and equipment is stated at cost and depreciated using the straight-line method over the estimated useful life of the related assets, which is generally five years. Leasehold improvements are amortized over the shorter of the lease term or estimated useful life of the related assets. Repairs and maintenance costs are charged to expense as incurred. Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are recorded as other assets, accounts payable and accrued expenses, and other long-term liabilities within the consolidated balance sheet. 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. Revenue Recognition To date, substantially all of the Company’s revenue has been derived from its prior license agreements. The terms of these arrangements included 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. I n accordance with Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers , 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 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 revenues 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, 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 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 each of the three years in the period ended December 31, 2020, there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials. Research and Development Costs Research and development costs, including license fees, are expensed as incurred. Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain. Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of employee 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 closing sales price for such stock on the date of grant. Equity award forfeitures are recorded as they occur. Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than‑not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability. 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): December 31, 2020 2019 2018 Warrants to purchase common stock 4,810,409 1,561,903 1,561,903 Common stock options and RSUs 601,481 370,391 300,738 ESPP shares 5,349 1,322 1,275 Total 5,417,239 1,933,616 1,863,916 Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Short-Term Investments, Cash Eq

Short-Term Investments, Cash Equivalents and Fair Value Measurements	12 Months Ended
	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Short-Term Investments, Cash Equivalents and Fair Value Measurements	2. Short-Term Investments, Cash Equivalents and Fair Value Measurements At December 31, 2020, the Company’s short-term investments consisted of U.S. treasury securities and at December 31, 2019, the Company had no short-term investments. 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. 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): December 31, 2020 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 1,002 $ — $ — $ 1,002 U.S. treasury securities 3,999 — — 3,999 $ 5,001 $ — $ — $ 5,001 Classified as: Cash equivalents $ 1,002 Short-term investments 3,999 Total cash equivalents and short-term investments $ 5,001 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 December 31, 2020 Money market funds and U.S. treasury securities $ 5,001 $ — $ 5,001 $ —

Balance Sheet Details

Balance Sheet Details	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Balance Sheet Details	3. Balance Sheet Details Property and Equipment Property and equipment consisted of the following (in thousands): December 31, 2020 2019 Computer and office equipment $ 138 $ 133 Furniture and fixtures 19 19 Leasehold improvements 21 21 178 173 Less accumulated depreciation and amortization (162) (150) $ 16 $ 23 Depreciation expense related to property and equipment totaled approximately $12,000, $22,000 and $28,000 for the years ended December 31, 2020, 2019 and 2018, respectively. Accounts payable and accrued expenses Accounts payable and accrued expenses consisted of the following (in thousands): December 31, 2020 2019 Accounts payable $ 1,725 $ 2,408 Accrued clinical related expenses 3,559 4,231 Other accruals 533 881 Current portion of operating lease liability 418 355 $ 6,235 $ 7,875

Long-Term Debt

Long-Term Debt	12 Months Ended
	Dec. 31, 2020
Debt Disclosure [Abstract]
Long-Term Debt	4. Long-Term Debt Long-term debt and unamortized debt discount balances were as follows (in thousands): December 31, 2020 2019 Long-term debt $ 4,200 $ 5,600 Less debt discount, net of current portion (9) (61) Long-term debt, net of debt discount 4,191 5,539 Less current portion of long-term debt (2,800) (2,800) Long-term debt, less current portion $ 1,391 $ 2,739 Current portion of long-term debt $ 2,800 $ 2,800 Current portion of debt discount (82) (196) Current portion of long-term debt, net $ 2,718 $ 2,604 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 At maturity (or earlier prepayment), the Company is required to make a final payment equal to 4.0% of the original principal amount borrowed. The 2018 Amended SVB Loan provides for prepayment fees of 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 December 31, 2020, the Company was in compliance with all covenants and conditions of the 2018 Amended SVB Loan. In connection with the 2018 Amended SVB Loan, the Company issued SVB a warrant to purchase 5,363 shares of its common stock at an exercise price of $26.10 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 December 31, 2020, 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 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 May 3, 2025 5,363 $ 26.10 15,747 Future minimum principal and interest payments under the 2018 Amended SVB Loan, including the final payment, as of December 31, 2020 are as follows (in thousands): 2021 $ 3,066 2022 1,717 4,783 Less interest and final payment (583 ) Long-term debt $ 4,200

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2020
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies 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 sublicensing fees. Each of the license agreements is generally cancelable by the Company, given appropriate prior written notice. At December 31, 2020, potential future milestone payments under these agreements, including future milestone payments associated with TRC253 acquired from Janssen Pharmaceutica N.V. (Janssen) as discussed in Note 7, totaled an aggregate of $54.6 million.

Stockholders' Equity

Stockholders' Equity	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Stockholders' Equity	6. Stockholders’ Equity Authorized Shares of Common Stock In December 2020, the Company’s stockholders approved a proposal to amend the Company’s Amended and Restated Certificate of Incorporation, as amended, and increased the 20,000,000 shares of common stock previously authorized to 40,000,000 shares. Sales of Common Stock In December 2020, the Company sold 1,612,844 shares of its common stock at an average purchase price of $8.84 for net proceeds of $13.6 million in two registered direct offerings with certain institutional investors. In August 2020, the Company sold 2,633,838 shares of its common stock at an average purchase price of $1.66 per share and warrants to purchase 3,429,696 shares of its common stock at an average purchase price of $1.64 per share with an exercise price of $0.01 per share (the 2020 Pre-Funded Warrants) for net proceeds of approximately $10.0 million in a private placement with multiple accredited institutional health care focused funds. In accordance with their terms, the 2020 Pre-Funded Warrants may not be exercised if the holder’s ownership of the Company’s common stock would exceed 19.99% of the Company’s total shares outstanding following such exercise. The 2020 Pre-Funded Warrants were recorded as a component of stockholders’ equity within additional paid-in capital on the consolidated balance sheets. In October 2019, as amended in April 2020, the Company entered into a Common Stock Purchase Agreement (the 2019 Purchase Agreement) with Aspire Capital which provides that, upon the terms and subject to the conditions and limitations set forth in the 2019 Purchase Agreement, Aspire Capital is committed to purchase up to an aggregate of $15.0 million of shares of the Company’s common stock solely at the Company’s request from time to time during the 30 month period of the agreement and at prices based on the market price at the time of each sale. In consideration for entering into the 2019 Purchase Agreement and concurrently with the execution of the 2019 Purchase Agreement, the Company issued 142,658 shares of its common stock to Aspire Capital. As of December 31, 2020, the Company had sold an aggregate 4.8 million shares of common stock under the 2019 Purchase Agreement with Aspire Capital for net proceeds of $9.6 million. In March and April 2018, the Company sold 1,193,059 shares of its common stock at a purchase price of $27.00 per share, warrants to purchase 176,554 shares of its common stock at a purchase price of $26.90 per share and an exercise price of $0.10 per share (the 2018 Pre-Funded Warrants) and warrants to purchase 1,369,602 shares of its common stock at a purchase price of $1.25 per share and an exercise price of $27.00 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 2018 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 2018 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 at that time, 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 December 2020, the Company entered into a Capital on Demand TM In connection with entering into the JonesTrading Agreement in December 2020, the Company terminated its prior Capital on Demand™ Sales Agreement, dated September 6, 2018, with JonesTrading and no further sales of common stock will occur under the prior sales agreement. As of December 31, 2020, the Company had sold an aggregate 3.0 million shares of common stock for net proceeds of $7.1 million under the prior sales agreement with JonesTrading. Common Stock Warrants As of December 31, 2020 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 March 27, 2025 176,554 $ 0.10 May 3, 2025 5,363 $ 26.10 August 27, 2027 1,889,513 $ 0.01 August 31, 2027 1,358,993 $ 0.01 4,810,409 During the year ended December 31, 2020, 181,190 pre-funded warrants were exercised for net proceeds of $2,000. Stock Compensation Plans 2015 Equity Incentive Plan Effective January 1, 2015, the Company’s board of directors adopted the 2015 Plan. Under the 2015 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company or its subsidiaries. Initially, a total of 80,103 shares of common stock were reserved for issuance under the 2015 Plan. In addition, the number of shares of common stock available for issuance under the 2015 Plan will be annually increased on the first day of each fiscal year during the term of the 2015 Plan, beginning with the 2016 fiscal year, by an amount equal to 4% of the total number of shares of common stock outstanding on December 31st of the preceding calendar year or such other amount as the Company’s board of directors may determine. The maximum term of the options granted under the 2015 Plan is no more than ten years. Grants generally vest at 25% one year from the vesting commencement date and ratably each month thereafter for a period of 36 months, subject to continuous service. In December 2015, the 2015 Plan was amended to allow an additional 50,000 shares of common stock to be used exclusively for the grant of equity awards as a material inducement for individuals to commence employment at the Company in compliance with Nasdaq Listing Rule 5635(c)(4). Restricted Stock Units In 2016, the Company issued RSUs to employees and members of the Company’s board of directors under the 2015 Plan. The total grant-date fair value of RSUs that vested during the years ended December 31, 2020 and 2019 was $0.3 million and $0.4 million, respectively. As of December 31, 2020, there were no outstanding RSUs. Restricted stock unit activity under the 2015 Plan is summarized as follows: Weighted Average Number of Grant Date Shares Fair Value Outstanding at December 31, 2019 3,520 $ 79.20 Granted — — Vested (3,520 ) $ 79.20 Forfeited — — Outstanding at December 31, 2020 — $ 79.20 Stock Options Stock option activity under all Plans is summarized as follows: Weighted- Number of Average Options Exercise Price Balance at December 31, 2019 366,871 $ 36.62 Granted 295,510 $ 3.62 Exercised — — Forfeited (60,900 ) $ 25.88 Balance at December 31, 2020 601,481 $ 21.50 Information about the Company’s outstanding stock options as of December 31, 2020 is as follows: Weighted- Average Weighted- Remaining Average Contractual Aggregate Number of Exercise Term Intrinsic Shares Price (in years) Value Options outstanding 601,481 $ 21.50 7.57 $ 2,746,663 Options vested and expected to vest 601,481 $ 21.50 7.57 $ 2,746,663 Options exercisable 252,565 $ 43.20 5.82 $ 362,644 The weighted-average grant date fair value per share of employee option grants during the years ended December 31, 2020, 2019 and 2018 was $2.62, $5.55 and $16.69, respectively. The aggregate intrinsic value used in the above table of options at December 31, 2020 is based on the Company’s closing market price per common share on December 31, 2020 of $11.70. No stock options were exercised during the years ended December 31, 2020 and 2019. The Company received approximately $0.2 million in proceeds from the exercise of stock options during the year ended December 31, 2018. The total intrinsic value of options exercised was approximately $0.2 million during the year ended December 31, 2018. The total grant-date fair value of options that vested during the years ended December 31, 2020, 2019 and 2018 was $1.0 million, $1.5 million and $2.6 million, respectively. Employee Stock Purchase Plan (ESPP) On January 1, 2015, the Company’s board of directors adopted the ESPP, which became effective upon the pricing of the Company’s initial public offering on January 29, 2015. The ESPP permits participants to purchase common stock through payroll deductions of up to 15% of their eligible compensation. Initially, a total of 18,346 shares of common stock was reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be annually increased on the first day of each fiscal year during the term of the ESPP, beginning with the 2016 fiscal year, by an amount equal to the lessor of: (i) 36,692 shares; (ii) 1% of the total number of shares of common stock outstanding on December 31st of the preceding calendar year; or (iii) such other amount as the Company’s board of directors may determine. Stock compensation expense for the years ended December 31, 2020, 2019 and 2018 related to the ESPP was immaterial. 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: Years Ended December 31, 2020 2019 2018 Risk-free interest rate 1.2 % 2.6 % 2.8% Expected volatility 85.8 % 81.1 % 79.6% Expected term (in years) 6.2 6.2 6.2 Expected dividend yield — — — Risk-free interest rate. The Company bases the risk‑free interest rate assumption on the U.S. Treasury’s rates for U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued. Expected volatility. The Company considers its historical volatility when determining the expected volatility. Expected term. The expected term represents the period of time that options are expected to be outstanding. Because the Company does not have historical exercise behavior, it determines the expected life assumption using the simplified method, which is an average of the contractual term of the option and its vesting period. Expected dividend yield. The Company bases the expected dividend yield assumption on the fact that it has never paid cash dividends and has no present intention to pay cash dividends. The allocation of stock-based compensation expense was as follows (in thousands): Years Ended December 31, 2020 2019 2018 Research and development $ 386 $ 776 $ 1,462 General and administrative 648 848 1,205 $ 1,034 $ 1,624 $ 2,667 As of December 31, 2020 and 2019, the unrecognized compensation cost related to outstanding time-based options was $1.3 million and $1.6 million, respectively, and is expected to be recognized as expense over approximately 2.6 years and 2.6 years, respectively. Common Stock Reserved for Future Issuance Common stock reserved for future issuance was as follows: December 31, 2020 2019 Common stock warrants 4,810,409 1,561,903 Common stock options and RSUs granted and outstanding 601,481 370,391 Awards available under the 2015 Plan 57,468 128,589 Shares available under the Employee Stock Purchase Plan 105,614 73,470 5,574,972 2,134,353

Collaborations

Collaborations	12 Months Ended
	Dec. 31, 2020
Collaborations Disclosure [Abstract]
Collaborations	7. Collaborations 3D Medicines and Alphamab In December 2019, the Company, 3D Medicines Co., Ltd. (3D Medicines), and Jiangsu Alphamab Biopharmaceuticals Co., Ltd. (Alphamab) entered into the Envafolimab Collaboration Agreement for the development of envafolimab, also known as KN035, an investigational PD-L1 sdAb, or nanobody, administered by subcutaneous injection, for the treatment of sarcoma in North America. No consideration was exchanged in the Envafolimab Collaboration Agreement. Given no consideration was exchanged, no value was assigned to the Envafolimab Collaboration Agreement in the accompanying consolidated balance sheets. Pursuant to the Envafolimab Collaboration Agreement, the Company was granted an exclusive license to develop and commercialize envafolimab for the treatment of sarcoma in North America. The Company is responsible for conducting, and will bear the costs of Phase 1, Phase 2, and Phase 3 or post-approval clinical trials in North America for envafolimab in the indications of refractory and first line treatment of sarcoma. 3D Medicines and Alphamab are responsible for conducting, and will bear the costs of, investigational new drug (IND)-enabling studies (other than those specific to the sarcoma indication) and the preparation of chemistry, manufacturing and controls (CMC) activities sections of an IND application for envafolimab. 3D Medicines and Alphamab have agreed to manufacture and supply, or to arrange for a third party manufacturer to manufacture and supply, envafolimab to the Company at pre-negotiated prices that vary based on clinical or commercial use. 3D Medicines and Alphamab retained the right to develop envafolimab in all territories outside of North America as well as within North America for all indications other than sarcoma. The Company will be responsible for commercializing envafolimab for sarcoma in North America, including booking of sales revenue, unless (a) envafolimab is first approved in North America for an indication other than sarcoma and launched in North America, or (b) envafolimab is first approved in North America for sarcoma and subsequently approved in North America for an additional non-orphan indication and sold commercially by 3D Medicines and/or Alphamab, or licensee, in which case 3D Medicines and Alphamab will be responsible for commercializing envafolimab for sarcoma in North America, including booking of sales revenue. If 3D Medicines and Alphamab become responsible for commercialization under the Envafolimab Collaboration Agreement, the Company has the option to co-market envafolimab for sarcoma in North America. In the event that envafolimab is first approved in North America for sarcoma and within three years of the commercial launch of envafolimab in North America for sarcoma 3D Medicines and Alphamab replace the Company as the party responsible for commercialization, and the Company elects and 3D Medicines and Alphamab agree for the Company to not co-market envafolimab for sarcoma in North America, then 3D Medicine and Alphamab will be required to compensate the Company for its costs associated with preparing for and conducting commercial activities. If the Company has the responsibility for commercialization under the Envafolimab Collaboration Agreement, the Company will owe 3D Medicines and Alphamab tiered double digit royalties on net sales of envafolimab for sarcoma in North America ranging from the teens to mid-double digits. If 3D Medicines and Alphamab have responsibility for commercialization under the Envafolimab Collaboration Agreement, the Company will be entitled to (a) escalating double digit royalties on net sales of envafolimab for sarcoma in North America ranging from the teens to mid-double digits if the Company has chosen to not co-market envafolimab in sarcoma or (b) a 50% royalty on net sales of envafolimab for sarcoma in North America if the Company has chosen to co-market envafolimab in sarcoma. Payment obligations under the Envafolimab Collaboration Agreement continue on a country-by-country basis until the last to expire licensed patent covering envafolimab expires. 3D Medicines and Alphamab retain the right to reacquire the rights to envafolimab for sarcoma in North America in connection with an arm’s length sale to a third party, provided that the sale may not occur prior to completion of a pivotal trial of envafolimab in sarcoma without the Company’s written consent and the parties must negotiate in good faith and agree to fair compensation to be paid to the Company for the value of and opportunity represented by the required rights. Each party agreed that during the term of the Envafolimab Collaboration Agreement, it would not develop or license from any third party a monospecific inhibitor to PD-L1 or PD-1 in sarcoma. The term of the Envafolimab Collaboration Agreement continues until the later of the date the parties cease further development and commercialization of envafolimab for sarcoma in North America or the expiration of all payment obligations. The Envafolimab Collaboration Agreement may be terminated earlier by a party in the event of an uncured material breach by the other party or bankruptcy of the other party, or for safety reasons related to envafolimab. In the event the Company elects, or a joint steering committee determines, to cease further development or commercialization of envafolimab, or if the Company fails to use commercially reasonable efforts to develop (including progress in clinical trials) and commercialize envafolimab and does not cure such failure within a specified time period, then the Company’s rights and obligations under the Envafolimab Collaboration Agreement will revert to 3D Medicines and Alphamab. 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 sheets. TJ004309 Agreement Pursuant to the TJ004309 Agreement, the Company and I-Mab are collaborating 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. In March 2020, I-Mab issued a press release announcing a strategic partnership with Kalbe Genexine Biologics (KG Bio), whereby KG Bio received what the press release described as a right of first negotiation outside North America for TJ004309 for up to $340 million in potential payments to I-Mab. On April 8, 2020, the Company issued a notice of dispute to I-Mab as the Company believes it may be entitled to receive a payment under the TJ004309 Agreement, although I-Mab has disputed that any payment is due. The Company cannot currently estimate the likely outcome of the dispute under the TJ004309 Agreement. In February 2021, I-Mab sent the Company a notice purporting to terminate the TJ4309 Agreement, which would result in I-Mab owing the Company a prespecified early termination fee of $9.0 million. However, I-Mab does not have an option to terminate the TJ004309 Agreement without cause until the ongoing Phase 1 trial of TJ004309 is complete, and the Company therefore believes the TJ4309 Agreement has not been terminated and continues to perform its contractual obligations. The TJ004309 TJ004309 TJ004309 TJ004309 Bispecific Agreement Pursuant to the Bispecific Agreement, the Company and I-Mab may mutually select through a joint steering committee (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 trials, and the Company will be responsible for and will share equally with I-Mab in the costs of conducting Phase 3 or pivotal clinical trials, 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 trial for a product candidate or if I-Mab ceases to support development costs or pay its portion of Phase 3 clinical trial costs for a product candidate or the JSC decides to cease development over the Company’s objections after initiating Phase 3 clinical trials, 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 trial, 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 clinical trial 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 trial, 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 clinical trial but before completion of Phase 2 proof of concept clinical trial 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 trial, 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 clinical trial and before completion of pivotal trial 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 trial, 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 trials or after initiating Phase 3 clinical trials 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. In March 2020, the Company learned that I-Mab entered into two license and collaboration agreements with ABL Bio in July 2018 (ABL Bio License 1 and ABL Bio License 2). Under ABL Bio License 1, I-Mab granted to ABL Bio exclusive, worldwide (excluding Greater China), royalty-bearing rights to develop and commercialize a bispecific antibody (the BsAb) using certain monoclonal antibody sequences. Under ABL License 2, I-Mab and ABL agreed to collaborate to develop three PD-L1-based bispecific antibodies by using ABL Bio’s proprietary bispecific antibody technology and commercialize them in their respective territories, which, collectively, include China, Hong Kong, Macau, Taiwan and South Korea, and other territories throughout the rest of the world if both parties agree to do so in such other territories during the performance of the agreement. On April 8, 2020, the Company issued a notice of dispute regarding possible breach of the Bispecific Agreement related to I-Mab entering into ABL License 1 and ABL License 2. The Company cannot currently estimate the likely outcome of the dispute under the Bispecific Agreement. Until these discussions are complete, the Company may be unable to provide a timeline as to when or if it will file an IND for a bispecific antibody under the Bispecific Agreement. 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 was permitted to use, develop, manufacture and commercialize carotuximab products for ophthalmology indications, excluding systemic treatment of ocular tumors. Santen also had the right to grant sublicenses to affiliates and third party collaborators. In the event Santen sublicensed any of its rights under the agreement, Santen would have been obligated to pay the Company a portion of any upfront and certain milestone payments received under such sublicense. Santen had sole responsibility for funding, developing, seeking regulatory approval for and commercializing carotuximab products in the field of ophthalmology. In the event that Santen failed to meet certain commercial diligence obligations, the Company would have had the option to co-promote carotuximab products in the field of ophthalmology in the United States with Santen. If the Company exercised this option, the Company would have been obligated to pay Santen a percentage of certain development expenses, and the Company would have received a percentage of profits from sales of the licensed products in the ophthalmology field in the United States, but would not also receive royalties on such sales. In March 2020, Santen announced the discontinuation of development of carotuximab, and in June 2020 terminated the agreement. No revenue was recognized related to this agreement for the years ended December 31, 2020, 2019 and 2018 and no further revenue will be recognized in connection with this agreement as Santen has terminated the carotuximab program. 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). With respect to the AR Mutant Program, the License and Option Agreement, as amended, provided Janssen with an option, which was exercisable until 90 days after the Company demonstrated 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. In April 2020, Janssen notified the Company that it would not regain the rights to TRC253. Therefore, the Company now retains worldwide development and commercialization rights to the AR Mutant Program and is 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 sheets. The Company is obligated to use diligent efforts to develop the AR Mutant Program according to agreed upon development plans, timelines and budgets. The Company is further obligated as it relates to the AR Mutant Program 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 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 .

Leases

Leases	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Leases	8. 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 $0.4 million for each of the three years ended December 31, 2020, 2019 and 2018. As of December 31, 2020, the Company does not have any finance leases, nor any other operating leases. Supplemental cash flow information related to operating leases was as follows (in thousands): Years Ended December 31, 2020 2019 2018 Cash paid within operating cash flows $ 442 $ 423 $ 405 Supplemental balance sheet information related to operating leases was as follows (in thousands, except lease term and discount rate): December 31, 2020 2019 Reported as: Other assets (ROU asset) $ 508 $ 838 Accounts payable and accrued expenses (lease liability) $ 418 $ 355 Other long-term liabilities (lease liability) 152 570 Total lease liabilities $ 570 $ 925 Weighted average remaining lease term 1.3 2.3 Weighted average discount rate 11.3 % 11.3 % As of December 31, 2020 2021 $ 461 2022 156 Total lease payments 617 Less imputed interest (47) Total operating lease liabilities $ 570 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.

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands): Years Ended December 31, 2020 2019 2018 Federal income taxes $ (3,523 ) $ (4,761 ) $ (7,341) State income taxes, net of federal benefit (1,084 ) (1,381 ) (2,340) Permanent items 104 149 439 Uncertain tax positions 1,224 1,828 672 Research and development credits (555 ) (1,253 ) (2,545) Rate change — — 629 Other, net — (75 ) — Stock compensation 113 395 66 Change in valuation allowance 3,721 5,098 10,420 Provision for income taxes $ — $ — $ — Significant components of the Company’s deferred tax assets and deferred tax liabilities are summarized as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 40,103 $ 36,850 Research and development credits and Orphan Drug Credit 9,321 8,944 Depreciation and amortization 258 269 Right-of-use liability 120 194 Other, net 1,476 1,369 Total deferred tax assets 51,278 47,626 Right-of-use asset (107 ) (176) Total deferred tax liabilities (107 ) (176) Total net deferred 51,171 47,450 Valuation allowance (51,171 ) (47,450) Net deferred tax assets $ — $ — The Company has net deferred tax assets relating primarily to net operating loss (NOL) carryforwards, research and development and Orphan Drug tax credit carryforwards. Subject to certain limitations, the Company may use these deferred tax assets to offset taxable income in future periods. Due to the Company’s history of losses and uncertainty regarding future earnings, a full valuation allowance has been recorded against the Company’s deferred tax assets, as it is more likely than not that such assets will not be realized. The net change in the total valuation allowance for the years ended December 31, 2020, 2019 and 2018 was $3.7 million, $5.1 million and $10.4 million, respectively. At December 31, 2020, the Company had federal and California NOL carryforwards of approximately $152.5 million and $117.7 million, respectively. The federal and California NOL carryforwards will begin to expire in 2030, unless previously utilized. In response to the COVID-19 global pandemic, the CARES Act was enacted on March 27, 2020, to provide aid and economic stimulus to the economy. Among other provisions, the CARES Act eliminates the 80% NOL limitation for tax years 2018, 2019, and 2020, and allows NOLs generated in those years to be carried back for five years. Due to the enactment of the CARES Act, we are currently unable to quantify the impact that the CARES Act will have on our financial position, results of operations or cash flows, although we do not anticipate the impact to be significant. At December 31, 2020, the Company also had federal and California research and development and Orphan Drug credit carryforwards of approximately $10.3 million and $2.5 million, respectively. The federal research and development and Orphan Drug credit carryforwards will begin expiring in 2031 unless previously utilized. The California research credit will carry forward indefinitely under current law. Pursuant to Sections 382 and 383 of the Internal Revenue Code (Code), the annual use of the Company’s NOL and research and development credit carryforwards may be limited in the event that a cumulative change in ownership of more than 50% occurs within a three-year period. The Company previously completed a Section 382/383 analysis regarding the limitation of NOL and research and development credit carryforwards as of December 31, 2018 and did not identify any change in ownership of more than 50% within the preceding three-year period since an ownership change was determined to have occurred at the time of the Company’s initial public offering in January 2015. The Company has not completed a study to assess whether an ownership change has occurred or whether there have been multiple ownership changes since December 31, 2018. If the Company has experienced an ownership change at any time since December 31, 2018, utilization of the NOL or R&D credit carryforwards would be subject to an annual limitation under Section 382 of the Code. Any limitation may result in expiration of a portion of the NOL or R&D credit carryforwards before utilization. Any carryforwards that will expire prior to utilization as a result of such limitations will be removed from deferred tax assets with a corresponding reduction of the valuation allowance with no net effect on income tax expense or the effective tax rate. The changes in the Company’s unrecognized tax benefits are summarized as follows (in thousands): Balance at December 31, 2017 $ 2,166 Change related to prior year positions — Increase related to current year positions 693 Balance at December 31, 2018 2,859 Change related to prior year positions — Increase related to current year positions 2,233 Balance at December 31, 2019 5,092 Change related to prior year positions — Increase related to current year positions 1,518 Balance at December 31, 2020 $ 6,610 The Company’s policy is to include interest and penalties related to unrecognized income tax benefits as a component of income tax expense. The Company has no accruals for interest or penalties in the accompanying consolidated balance sheets as of December 31, 2020 and 2019 and has not recognized interest or penalties in the accompanying consolidated statements of operations for the three years in the period ended December 31, 2020. Due to the valuation allowance recorded against the Company’s deferred tax assets, future changes in unrecognized tax benefits will not impact the Company’s effective tax rate. The Company does not expect its unrecognized tax benefits to change significantly in the next 12 months. The Company is subject to taxation in the United States and California. Due to the net operating loss carryforwards, the U.S. federal and California returns are open to examination for all years since inception. The Company has not been, nor is it currently, under examination by the federal or any state tax authority.

401(k) Plan

401(k) Plan	12 Months Ended
	Dec. 31, 2020
Compensation And Retirement Disclosure [Abstract]
401(k) Plan	10. 401(k) Plan The Company maintains a defined contribution 401(k) plan available to eligible employees. Employee contributions are voluntary and are determined on an individual basis, limited to the maximum amount allowable under federal tax regulations. The Company, at its discretion, may make certain matching contributions to the 401(k) plan. Matching contributions for the years ended December 31, 2020, 2019 and 2018 totaled $0.1 million, $0.2 million and $0.2 million, respectively.

Organization and Summary of S_2

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2020
Organization And Accounting Policies [Abstract]
Organization and Business	Organization and Business TRACON Pharmaceuticals, Inc. (TRACON or the Company) was incorporated in the state of Delaware on October 28, 2004. TRACON is a biopharmaceutical company focused on the development and commercialization of novel targeted therapeutics for cancer, and utilizes its cost efficient, contract research organization (CRO) independent product development platform to partner with ex-U.S. companies to develop and commercialize innovative products in the United States. The 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 December 31, 2020, 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 December 31, 2020, the Company had an accumulated deficit of $179.1 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 December 31, 2020, the Company had cash, cash equivalents, and short-term investments of $36.1 million. Based on the Company’s current business plan, management believes that existing cash, cash equivalents, and short-term investments will be sufficient to fund the Company’s obligations for a period in excess of one year from the date of issuance of these financial statements. The completion of the two registered direct offerings in December 2020, which generated net proceeds of $13.6 million, the completion of the private placement of the Company’s common stock and pre-funded warrants in August 2020, which generated net proceeds to the Company of $10.0 million, the sale of the Company’s common stock under the common stock purchase agreement with Aspire Capital Fund, LLC (Aspire Capital), which generated net proceeds of $9.6 million during 2020, and the sale of the Company’s common stock under its prior Capital on Demand™ sales agreement with JonesTrading Institutional Services LLC (JonesTrading), which generated net proceeds of $4.8 million during 2020, alleviated the substantial doubt about the Company’s ability to continue as a going concern which existed at the reporting date of the December 31, 2019 consolidated financial statements. The Company plans to continue to fund its losses from operations through its existing cash, cash equivalents, and short-term investments, as well as through future equity offerings, debt financings, other third party funding, and potential licensing or collaboration arrangements. In addition, the Company may fund its losses from operations through the common stock purchase agreement the Company entered into with Aspire Capital in October 2019, as amended in April 2020, for the purchase of up to $15.0 million of the Company’s common stock over the 30 month period of the purchase agreement, $5.4 million of which remained available for sale , TM
Risks And Uncertainties	Risks and Uncertainties In December 2019, COVID-19, a novel strain of coronavirus, was first reported in Wuhan, China and has since become a global pandemic. The virus continues to spread globally, has been declared a pandemic by the World Health Organization and has spread to over The Company has experienced temporary closures of its offices in light of state and local orders and most of its employees continue to work remotely. In addition, the Company’s employees have not been able to conduct normal business travel, in particular as part of business development activities or in-person monitoring of clinical trial sites. Potential further impacts to the Company’s business include, but are not limited to, additional closures of its facilities or those of its vendors, continued disruptions or restrictions on its employees’ ability to travel, disruptions to or delays in ongoing clinical trials, third-party manufacturing supply and other operations, the potential diversion of healthcare resources away from the conduct of clinical trials to focus on pandemic concerns, interruptions or delays in the operations of the U.S. Food and Drug Administration or other regulatory authorities, and the Company’s ability to raise capital and conduct business development activities.
Use of Estimates	Use of Estimates The Company’s consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States (GAAP). The preparation of the Company’s 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 expenses incurred for clinical trials. 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. The Company is not aware of any specific event or circumstance that would require an update to its estimates, judgments and assumptions or a revision of the carrying value of the Company's assets or liabilities as of the date of this filing.
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 and cash equivalents. 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.
Property and Equipment	Property and Equipment Property and equipment is stated at cost and depreciated using the straight-line method over the estimated useful life of the related assets, which is generally five years. Leasehold improvements are amortized over the shorter of the lease term or estimated useful life of the related assets. Repairs and maintenance costs are charged to expense as incurred.
Leases	Leases The Company determines if an arrangement contains a lease at inception. For arrangements where the Company is the lessee, operating leases are recorded as other assets, accounts payable and accrued expenses, and other long-term liabilities within the consolidated balance sheet. 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.
Revenue Recognition	Revenue Recognition To date, substantially all of the Company’s revenue has been derived from its prior license agreements. The terms of these arrangements included 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. I n accordance with Accounting Standards Update (ASU) No. 2014-09, Revenue from Contracts with Customers , 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 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 revenues 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, 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 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 each of the three years in the period ended December 31, 2020, there were no material adjustments to the Company’s prior period estimates of accrued expenses for clinical trials.
Research and Development Costs	Research and Development Costs Research and development costs, including license fees, are expensed as incurred.
Patent Costs	Patent Costs Costs related to filing and pursuing patent applications are recorded as general and administrative expense and expensed as incurred since recoverability of such expenditures is uncertain.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense represents the grant date fair value of employee 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 closing sales price for such stock on the date of grant. Equity award forfeitures are recorded as they occur.
Income Taxes	Income Taxes The Company accounts for income taxes under the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been included in the financial statements. Under this method, deferred tax assets and liabilities are determined on the basis of the differences between the financial statements and tax basis of assets and liabilities using enacted tax rates in effect for the year in which the differences are expected to reverse. The effect of a change in tax rates on deferred tax assets and liabilities is recognized as income in the period that includes the enactment date. The Company recognizes net deferred tax assets to the extent that the Company believes these assets are more likely than not to be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, tax-planning strategies, and results of recent operations. If management determines that the Company would be able to realize its deferred tax assets in the future in excess of their net recorded amount, management would make an adjustment to the deferred tax asset valuation allowance, which would reduce the provision for income taxes. The Company records uncertain tax positions on the basis of a two-step process whereby (1) management determines whether it is more likely than not that the tax positions will be sustained on the basis of the technical merits of the position and (2) for those tax positions that meet the more-likely-than‑not recognition threshold, management recognizes the largest amount of tax benefit that is more than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company recognizes interest and penalties related to unrecognized tax benefits within income tax expense. Any accrued interest and penalties are included within the related tax liability.
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): December 31, 2020 2019 2018 Warrants to purchase common stock 4,810,409 1,561,903 1,561,903 Common stock options and RSUs 601,481 370,391 300,738 ESPP shares 5,349 1,322 1,275 Total 5,417,239 1,933,616 1,863,916
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations and manages its business in one operating segment.

Organization and Summary of S_3

Organization and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2020
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): December 31, 2020 2019 2018 Warrants to purchase common stock 4,810,409 1,561,903 1,561,903 Common stock options and RSUs 601,481 370,391 300,738 ESPP shares 5,349 1,322 1,275 Total 5,417,239 1,933,616 1,863,916

Short-Term Investments, Cash _2

Short-Term Investments, Cash Equivalents and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2020
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): December 31, 2020 Cost Unrealized Gain Unrealized (Loss) Estimated Fair Value Money market funds $ 1,002 $ — $ — $ 1,002 U.S. treasury securities 3,999 — — 3,999 $ 5,001 $ — $ — $ 5,001 Classified as: Cash equivalents $ 1,002 Short-term investments 3,999 Total cash equivalents and short-term investments $ 5,001
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 December 31, 2020 Money market funds and U.S. treasury securities $ 5,001 $ — $ 5,001 $ —

Balance Sheet Details (Tables)

Balance Sheet Details (Tables)	12 Months Ended
	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Schedule Of Property and Equipment	Property and equipment consisted of the following (in thousands): December 31, 2020 2019 Computer and office equipment $ 138 $ 133 Furniture and fixtures 19 19 Leasehold improvements 21 21 178 173 Less accumulated depreciation and amortization (162) (150) $ 16 $ 23
Schedule Of Accounts Payable and Accrued Expenses	Accounts payable and accrued expenses consisted of the following (in thousands): December 31, 2020 2019 Accounts payable $ 1,725 $ 2,408 Accrued clinical related expenses 3,559 4,231 Other accruals 533 881 Current portion of operating lease liability 418 355 $ 6,235 $ 7,875

Long-Term Debt (Tables)

Long-Term Debt (Tables)	12 Months Ended
	Dec. 31, 2020
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): December 31, 2020 2019 Long-term debt $ 4,200 $ 5,600 Less debt discount, net of current portion (9) (61) Long-term debt, net of debt discount 4,191 5,539 Less current portion of long-term debt (2,800) (2,800) Long-term debt, less current portion $ 1,391 $ 2,739 Current portion of long-term debt $ 2,800 $ 2,800 Current portion of debt discount (82) (196) Current portion of long-term debt, net $ 2,718 $ 2,604
Schedule of exercisable outstanding warrants for purchase of common stock issued	At December 31, 2020, 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 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 May 3, 2025 5,363 $ 26.10 15,747 As of December 31, 2020 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 March 27, 2025 176,554 $ 0.10 May 3, 2025 5,363 $ 26.10 August 27, 2027 1,889,513 $ 0.01 August 31, 2027 1,358,993 $ 0.01 4,810,409 During the year ended December 31, 2020, 181,190 pre-funded warrants were exercised for net proceeds of $2,000.
Schedule of future minimum principal and interest payments	Future minimum principal and interest payments under the 2018 Amended SVB Loan, including the final payment, as of December 31, 2020 are as follows (in thousands): 2021 $ 3,066 2022 1,717 4,783 Less interest and final payment (583 ) Long-term debt $ 4,200

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	12 Months Ended
	Dec. 31, 2020
Stockholders Equity Note [Abstract]
Schedule of exercisable outstanding warrants for purchase of common stock issued	At December 31, 2020, 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 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 May 3, 2025 5,363 $ 26.10 15,747 As of December 31, 2020 , the Company had the following outstanding warrants for the purchase of common stock: Expiration Number of shares Exercise price May 13, 2022 1,841 $ 108.60 November 14, 2023 through June 4, 2024 3,874 $ 77.40 January 25, 2024 4,669 $ 51.40 March 27, 2024 1,369,602 $ 27.00 March 27, 2025 176,554 $ 0.10 May 3, 2025 5,363 $ 26.10 August 27, 2027 1,889,513 $ 0.01 August 31, 2027 1,358,993 $ 0.01 4,810,409 During the year ended December 31, 2020, 181,190 pre-funded warrants were exercised for net proceeds of $2,000.
Schedule of restricted stock unit activity under 2015 plan	Restricted stock unit activity under the 2015 Plan is summarized as follows: Weighted Average Number of Grant Date Shares Fair Value Outstanding at December 31, 2019 3,520 $ 79.20 Granted — — Vested (3,520 ) $ 79.20 Forfeited — — Outstanding at December 31, 2020 — $ 79.20
Schedule of stock option activity	Stock option activity under all Plans is summarized as follows: Weighted- Number of Average Options Exercise Price Balance at December 31, 2019 366,871 $ 36.62 Granted 295,510 $ 3.62 Exercised — — Forfeited (60,900 ) $ 25.88 Balance at December 31, 2020 601,481 $ 21.50
Schedule of outstanding stock options	Information about the Company’s outstanding stock options as of December 31, 2020 is as follows: Weighted- Average Weighted- Remaining Average Contractual Aggregate Number of Exercise Term Intrinsic Shares Price (in years) Value Options outstanding 601,481 $ 21.50 7.57 $ 2,746,663 Options vested and expected to vest 601,481 $ 21.50 7.57 $ 2,746,663 Options exercisable 252,565 $ 43.20 5.82 $ 362,644
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: Years Ended December 31, 2020 2019 2018 Risk-free interest rate 1.2 % 2.6 % 2.8% Expected volatility 85.8 % 81.1 % 79.6% Expected term (in years) 6.2 6.2 6.2 Expected dividend yield — — —
Summary of allocation of stock-based compensation expense	The allocation of stock-based compensation expense was as follows (in thousands): Years Ended December 31, 2020 2019 2018 Research and development $ 386 $ 776 $ 1,462 General and administrative 648 848 1,205 $ 1,034 $ 1,624 $ 2,667
Schedule of common stock reserved for future issuance	Common stock reserved for future issuance was as follows: December 31, 2020 2019 Common stock warrants 4,810,409 1,561,903 Common stock options and RSUs granted and outstanding 601,481 370,391 Awards available under the 2015 Plan 57,468 128,589 Shares available under the Employee Stock Purchase Plan 105,614 73,470 5,574,972 2,134,353

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2020
Leases [Abstract]
Schedule of supplemental Cash Flow Information Related to Operating Leases [Table Text Block]	Supplemental cash flow information related to operating leases was as follows (in thousands): Years Ended December 31, 2020 2019 2018 Cash paid within operating cash flows $ 442 $ 423 $ 405
Schedule of Supplemental Balance Sheet Information Related to Operating Leases [Table Text Block]	Supplemental balance sheet information related to operating leases was as follows (in thousands, except lease term and discount rate): December 31, 2020 2019 Reported as: Other assets (ROU asset) $ 508 $ 838 Accounts payable and accrued expenses (lease liability) $ 418 $ 355 Other long-term liabilities (lease liability) 152 570 Total lease liabilities $ 570 $ 925 Weighted average remaining lease term 1.3 2.3 Weighted average discount rate 11.3 % 11.3 %
Schedule of Maturities of Operating Lease Liabilities [Table Text Block]	As of December 31, 2020 2021 $ 461 2022 156 Total lease payments 617 Less imputed interest (47) Total operating lease liabilities $ 570

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2020
Income Tax Disclosure [Abstract]
Schedule of reconciliation of effective tax rate and federal statutory tax rate	A reconciliation of the Company’s effective tax rate and federal statutory tax rate is summarized as follows (in thousands): Years Ended December 31, 2020 2019 2018 Federal income taxes $ (3,523 ) $ (4,761 ) $ (7,341) State income taxes, net of federal benefit (1,084 ) (1,381 ) (2,340) Permanent items 104 149 439 Uncertain tax positions 1,224 1,828 672 Research and development credits (555 ) (1,253 ) (2,545) Rate change — — 629 Other, net — (75 ) — Stock compensation 113 395 66 Change in valuation allowance 3,721 5,098 10,420 Provision for income taxes $ — $ — $ —
Schedule of components of deferred tax assets and deferred tax Liabilities	Significant components of the Company’s deferred tax assets and deferred tax liabilities are summarized as follows (in thousands): December 31, 2020 2019 Deferred tax assets: Net operating loss carryforwards $ 40,103 $ 36,850 Research and development credits and Orphan Drug Credit 9,321 8,944 Depreciation and amortization 258 269 Right-of-use liability 120 194 Other, net 1,476 1,369 Total deferred tax assets 51,278 47,626 Right-of-use asset (107 ) (176) Total deferred tax liabilities (107 ) (176) Total net deferred 51,171 47,450 Valuation allowance (51,171 ) (47,450) Net deferred tax assets $ — $ —
Schedule of changes in unrecognized tax benefits	The changes in the Company’s unrecognized tax benefits are summarized as follows (in thousands): Balance at December 31, 2017 $ 2,166 Change related to prior year positions — Increase related to current year positions 693 Balance at December 31, 2018 2,859 Change related to prior year positions — Increase related to current year positions 2,233 Balance at December 31, 2019 5,092 Change related to prior year positions — Increase related to current year positions 1,518 Balance at December 31, 2020 $ 6,610

Organization and Summary of S_4

Organization and Summary of Significant Accounting Policies - Additional Information (Details)	1 Months Ended					12 Months Ended
	Dec. 31, 2020USD ($)	Aug. 30, 2020USD ($)	Oct. 31, 2019USD ($)	Apr. 30, 2018USD ($)	Mar. 31, 2018USD ($)	Dec. 31, 2020USD ($)segment	Dec. 31, 2019USD ($)
Basis of Presentation
Accumulated deficit	$ (179,109,000)					$ (179,109,000)	$ (162,334,000)
Cash, cash equivalents and short-term investments	36,100,000					$ 36,100,000
Property and Equipment
Estimated useful life						5 years
Segment reporting
Number of reportable segments | segment						1
Aspire Capital Fund L L C | Common Stock
Basis of Presentation
Proceeds From Issuance Of Common Stock						$ 9,600,000
Maximum aggregate value of common stock to be purchase			$ 15,000,000
Sale duration for common stock under purchase agreement			30 months
Private Placement | Pre Funded Common Warrants
Basis of Presentation
Net Proceeds Received From Issuance Private Placement		$ 10,000,000				13,600,000
Private Placement | Common Stock
Basis of Presentation
Net Proceeds Received From Issuance Private Placement		$ 10,000,000		$ 36,500,000	$ 36,500,000
Private Placement | Jones Trading Institutional Services L L C | Common Stock | Pre Funded Common Warrants
Basis of Presentation
Proceeds From Issuance Of Common Stock						4,800,000
Private Placement | Aspire Capital Fund L L C | Common Stock | Pre Funded Common Warrants
Basis of Presentation
Proceeds From Issuance Of Common Stock						9,600,000
Capital on Demand Sales Agreement | Jones Trading Institutional Services L L C
Basis of Presentation
Remaining amount available under the Sales Agreement	5,400,000					5,400,000
Capital on Demand Sales Agreement | Jones Trading Institutional Services L L C | Common Stock
Basis of Presentation
Proceeds From Issuance Of Common Stock	7,100,000
Maximum aggregate value of stock to be sold	$ 50,000,000					$ 50,000,000

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	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Antidilutive securities
Antidilutive securities	5,417,239	1,933,616	1,863,916
Warrants to Purchase Common Stock
Antidilutive securities
Antidilutive securities	4,810,409	1,561,903	1,561,903
Common Stock Options and Restricted Stock Units
Antidilutive securities
Antidilutive securities	601,481	370,391	300,738
ESPP Shares
Antidilutive securities
Antidilutive securities	5,349	1,322	1,275

Short-Term Investments, Cash _3

Short-Term Investments, Cash Equivalents and Fair Value Measurements - Additional Information (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Fair Value Disclosures [Abstract]
Short-term investments	$ 3,999,000	$ 0
Amount of transfers between levels	$ 0	$ 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	Dec. 31, 2020	Dec. 31, 2019
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	$ 5,001
Estimated Fair Value	5,001
Short-term investments	3,999	$ 0
Estimated Fair Value
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cash equivalents	1,002
Short-term investments	3,999
Money market funds
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	1,002
Estimated Fair Value	1,002
U.S. treasury securities
Short-Term Investments, Cash Equivalents and Fair Value Measurements
Cost	3,999
Estimated Fair Value	$ 3,999

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 $ in Thousands	Dec. 31, 2020USD ($)
Assets:
Fair value, assets	$ 5,001
Level 2
Assets:
Fair value, assets	$ 5,001

Balance Sheet Details - Schedul

Balance Sheet Details - Schedule Of Property and Equipment (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Public Utilities Inventory [Line Items]
Property and equipment	$ 178	$ 173
Leasehold improvements	21	21
Less accumulated depreciation and amortization	(162)	(150)
Property and equipment - net	16	23
Computer And Office Equipment [Member]
Public Utilities Inventory [Line Items]
Property and equipment	138	133
Furniture and Fixtures [Member]
Public Utilities Inventory [Line Items]
Property and equipment	$ 19	$ 19

Balance Sheet Details - Additio

Balance Sheet Details - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Commitments And Contingencies Disclosure [Abstract]
Depreciation expense related to property and equipment	$ 12,000	$ 22,000	$ 28,000

Balance Sheet Details - Sched_2

Balance Sheet Details - Schedule Of Accounts Payable and Accrued Expenses (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Public Utilities Inventory [Line Items]
Accounts payable	$ 1,725	$ 2,408
Accrued clinical related expenses	3,559	4,231
Other accruals	533	881
Current portion of operating lease liability	570	925
Total	6,235	7,875
Current Portion
Public Utilities Inventory [Line Items]
Current portion of operating lease liability	$ 418	$ 355

Long-Term Debt - Schedule of Lo

Long-Term Debt - Schedule of Long-Term Debt and Unamortized Debt Discount Balances (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Long-term debt
Long-term debt	$ 4,200	$ 5,600
Less debt discount, net of current portion	(9)	(61)
Long-term debt, net of debt discount	4,191	5,539
Less current portion of long-term debt	(2,800)	(2,800)
Long-term debt, less current portion	1,391	2,739
Current portion of long-term debt	2,800	2,800
Current portion of debt discount	(82)	(196)
Current portion of long-term debt, net	$ 2,718	$ 2,604

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended
	May 31, 2018	Dec. 31, 2020	Dec. 31, 2018
Debt Instrument [Line Items]
Proceeds from long-term debt			$ 7,000,000
Warrants issued		4,810,409
Silicon Valley Bank
Debt Instrument [Line Items]
Warrants issued		15,747
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	5,363
Exercise price (per share)	$ 26.10
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
Deferral Agreement | Silicon Valley Bank
Debt Instrument [Line Items]
Extension of period for interest only payments		6 months
Maturity date		Jun. 30, 2022
Description of extension of period for interest only payments		In April 2020, the Company entered into a deferral agreement with SVB (the Deferral Agreement) for an interest-only payment period of six months, with a corresponding six month extension to the maturity date to June 2022.

Long-Term Debt - Schedule of Ex

Long-Term Debt - Schedule of Exercisable Outstanding Warrants for Purchase of Common Stock Issued (Details)	Dec. 31, 2020$ / sharesshares
Debt Instrument [Line Items]
Warrants issued	4,810,409
Silicon Valley Bank
Debt Instrument [Line Items]
Warrants issued	15,747
Silicon Valley Bank | May 13, 2022
Debt Instrument [Line Items]
Warrants issued	1,841
Exercise price (per share) | $ / shares	$ 108.60
Silicon Valley Bank | November 14, 2023 Through June 4, 2024
Debt Instrument [Line Items]
Warrants issued	3,874
Exercise price (per share) | $ / shares	$ 77.40
Silicon Valley Bank | January 25, 2024
Debt Instrument [Line Items]
Warrants issued	4,669
Exercise price (per share) | $ / shares	$ 51.40
Silicon Valley Bank | May 3, 2025
Debt Instrument [Line Items]
Warrants issued	5,363
Exercise price (per share) | $ / shares	$ 26.10

Long-Term Debt - Schedule of Fu

Long-Term Debt - Schedule of Future Minimum Principal and Interest Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Long-term debt	$ 4,200	$ 5,600
2018 Amended SVB Loan
Debt Instrument [Line Items]
2021	3,066
2022	1,717
Long-term debt including final payment	4,783
Less interest and final payment	(583)
Long-term debt	$ 4,200

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) $ in Millions	Dec. 31, 2020USD ($)
Research and development arrangement
Commitments and Contingencies
Potential milestone payable	$ 54.6

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - USD ($)	1 Months Ended					12 Months Ended
	Dec. 31, 2020	Aug. 30, 2020	Oct. 31, 2019	Apr. 30, 2018	Mar. 31, 2018	Dec. 31, 2020	Dec. 31, 2018	Dec. 31, 2019
Class Of Stock [Line Items]
Common stock, shares authorized	40,000,000					40,000,000		20,000,000
Conversion of warrants to purchase shares	4,810,409					4,810,409
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 at that time, 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
2020 Pre-Funded Warrants
Class Of Stock [Line Items]
Warrants exercised						181,190
Proceeds from warrant exercises						$ 2,000
2020 Pre-Funded Warrants and Common Warrants
Class Of Stock [Line Items]
Maximum percentage of holders ownership interest in common stock after exercise		19.99%
2018 Pre-Funded Warrants and Common Warrants
Class Of Stock [Line Items]
Maximum percentage of holders ownership interest in common stock after exercise				19.99%	19.99%
Maximum percentage of holders ownership interest in common stock to exercise warrants.				9.99%	9.99%
Common Stock | Aspire Capital Fund L L C
Class Of Stock [Line Items]
Stock issued during period, shares, new issues			142,658			4,800,000
Proceeds From Issuance Of Common Stock						$ 9,600,000
Maximum aggregate value of common stock to be purchase			$ 15,000,000
Sale duration for common stock under purchase agreement			30 months
Common Stock | Direct Offerings
Class Of Stock [Line Items]
Stock issued during period, shares, new issues	1,612,844
Shares issued, price per share	$ 8.84					$ 8.84
Proceeds From Issuance Of Common Stock	$ 13,600,000
Common Stock | Private Placement
Class Of Stock [Line Items]
Stock issued during period, shares, new issues				1,193,059	1,193,059
Shares issued, price per share				$ 27	$ 27
Net Proceeds Received From Issuance Private Placement		$ 10,000,000		$ 36,500,000	$ 36,500,000
Common Stock | Private Placement | 2020 Pre-Funded Warrants
Class Of Stock [Line Items]
Exercise price (per share)		$ 0.01
Common Stock | Private Placement | 2018 Pre-Funded Warrants
Class Of Stock [Line Items]
Shares issued, price per share				$ 26.90	$ 26.90
Conversion of warrants to purchase shares				176,554	176,554
Exercise price (per share)				$ 0.10	$ 0.10
Common Stock | Private Placement | Common Warrants
Class Of Stock [Line Items]
Shares issued, price per share				$ 1.25	$ 1.25
Conversion of warrants to purchase shares				1,369,602	1,369,602
Exercise price (per share)				$ 27	$ 27
Common Stock | Private Placement | Purchase Price of $1.66 Per Share
Class Of Stock [Line Items]
Stock issued during period, shares, new issues		2,633,838
Shares issued, price per share		$ 1.66
Common Stock | Private Placement | Purchase Price of $1.64 Per Share | 2020 Pre-Funded Warrants
Class Of Stock [Line Items]
Shares issued, price per share		$ 1.64
Conversion of warrants to purchase shares		3,429,696
Common Stock | Capital on Demand Sales Agreement | Jones Trading Institutional Services L L C
Class Of Stock [Line Items]
Proceeds From Issuance Of Common Stock	7,100,000
Maximum aggregate value of stock to be sold	$ 50,000,000					$ 50,000,000
Percentage of gross proceeds, required to pay for common stock sold through sales agreement	2.50%
Sales Agreement Termination Date	Sep. 6, 2018
Stock issued during period, value, new issues	$ 3,000,000

Stockholders' Equity - Schedule

Stockholders' Equity - Schedule of Outstanding Warrants for Purchase of Common Stock Issued (Details)	Dec. 31, 2020$ / sharesshares
Class Of Stock [Line Items]
Warrants issued	4,810,409
May 13, 2022
Class Of Stock [Line Items]
Warrants issued	1,841
Exercise price (per share) | $ / shares	$ 108.60
November 14, 2023 Through June 4, 2024
Class Of Stock [Line Items]
Warrants issued	3,874
Exercise price (per share) | $ / shares	$ 77.40
January 25, 2024
Class Of Stock [Line Items]
Warrants issued	4,669
Exercise price (per share) | $ / shares	$ 51.40
March 27, 2024
Class Of Stock [Line Items]
Warrants issued	1,369,602
Exercise price (per share) | $ / shares	$ 27
March 27, 2025
Class Of Stock [Line Items]
Warrants issued	176,554
Exercise price (per share) | $ / shares	$ 0.10
May 3, 2025
Class Of Stock [Line Items]
Warrants issued	5,363
Exercise price (per share) | $ / shares	$ 26.10
August 27, 2027
Class Of Stock [Line Items]
Warrants issued	1,889,513
Exercise price (per share) | $ / shares	$ 0.01
August 31, 2027
Class Of Stock [Line Items]
Warrants issued	1,358,993
Exercise price (per share) | $ / shares	$ 0.01

Stockholders' Equity - (SBC) -

Stockholders' Equity - (SBC) - Additional Information (Details) - USD ($)	Jan. 02, 2015	Dec. 31, 2015	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Stock Plans
Shares of common stock reserved for future issuance			5,574,972	2,134,353
Stock Option
Share-based compensation
Unrecognized compensation cost			$ 1,300,000	$ 1,600,000
Unrecognized compensation cost, period of recognition			2 years 7 months 6 days	2 years 7 months 6 days
Stock options, additional disclosures
Granted (in dollars per share)			$ 2.62	$ 5.55	$ 16.69
Share price (in dollar per share)			$ 11.70
Proceeds from exercise of stock options					$ 200,000
Shares Options, Exercises in Period			0	0
Total intrinsic value of options exercised					200,000
Total fair value of options vested during the year			$ 1,000,000	$ 1,500,000	$ 2,600,000
Stock Option | Year One
Stock Plans
Grants vesting period			1 year
Grants vesting (as a percent)			25.00%
Stock Option | Thereafter
Stock Plans
Grants vesting period			36 months
ESPP
Stock Plans
Shares of common stock reserved for future issuance	18,346
Percentage of total number of shares of common stock outstanding	1.00%
Share-based compensation
Percentage of eligible compensation	15.00%
Stock options, additional disclosures
Number of shares that could potentially be issued	36,692
2015 Equity Incentive Plan
Stock Plans
Maximum term of options granted			10 years
Shares of common stock reserved for future issuance	80,103		57,468	128,589
Percentage of total number of shares of common stock outstanding	4.00%
Additional shares to be used exclusively for grant for Inducement awards		50,000
2015 Equity Incentive Plan | Restricted Stock Units
Share-based compensation
Aggregate intrinsic value of outstanding units			$ 0
2015 Equity Incentive Plan | Restricted Stock Units | Board of Directors
Share-based compensation
Total fair value of the units			$ 300,000	$ 400,000

Stockholders' Equity - Summary

Stockholders' Equity - Summary of Restricted Stock Unit Activity (Details) - Restricted Stock Units - 2015 Equity Incentive Plan	12 Months Ended
	Dec. 31, 2020$ / sharesshares
Number of Options
Balance (in shares) | shares	3,520
Vested (in shares) | shares	(3,520)
Balance (in shares) | shares
Weighted Average Grant Date Fair Value
Balance (in dollars per share) | $ / shares	$ 79.20
Vested (in dollars per share) | $ / shares	79.20
Balance (in dollars per share) | $ / shares	$ 79.20

Stockholders' Equity- Summary o

Stockholders' Equity- Summary of Stock Option Activity (Details) - Stock Option - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Balance (in shares)	366,871
Granted (in shares)	295,510
Exercised (in shares)	0	0
Forfeited (in shares)	(60,900)
Balance (in shares)	601,481	366,871
Weighted-Average Exercise Price
Balance (in dollars per share)	$ 36.62
Granted (in dollars per share)	3.62
Forfeited (in dollars per share)	25.88
Balance (in dollars per share)	$ 21.50	$ 36.62

Stockholders' Equity - Summar_2

Stockholders' Equity - Summary of Company's Outstanding Stock Option (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Options
Number of shares, options vested and expected to vest	601,481	370,391
Stock Option
Number of Options
Balance (in shares)	366,871
Number of shares, options vested and expected to vest	601,481
Number of shares, options exercisable	252,565
Aggregate intrinsic value, options outstanding	$ 2,746,663
Aggregate intrinsic value, options vested and expected to vest	2,746,663
Aggregate intrinsic value, options exercisable	$ 362,644
Weighted-Average Exercise Price
Balance (in shares)	$ 21.50	$ 36.62
Weighted-average exercise price, options vested and expected to vest (in dollars per share)	21.50
Weighted-average exercise price, options exercisable (in dollars per share)	$ 43.20
Weighted-average remaining contractual term, options outstanding (in years)	7 years 6 months 25 days
Weighted-average remaining contractual term, options vested and expected to vest (in years)	7 years 6 months 25 days
Weighted-average remaining contractual term, options exercisable (in years)	5 years 9 months 25 days

Stockholders' Equity - Summar_3

Stockholders' Equity - Summary of Weighted-Average Assumptions Fair Value of the Employee Stock Option Grants (Details) - Stock Option	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Risk-free interest rate	1.20%	2.60%	2.80%
Expected volatility	85.80%	81.10%	79.60%
Expected term (in years)	6 years 2 months 12 days	6 years 2 months 12 days	6 years 2 months 12 days
Expected dividend yield	0.00%	0.00%	0.00%

Stockholders' Equity (Deficit)

Stockholders' Equity (Deficit) - Summary of Allocation of Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Class Of Stock [Line Items]
Stock based compensation expense	$ 1,034	$ 1,624	$ 2,667
Research and development
Class Of Stock [Line Items]
Stock based compensation expense	386	776	1,462
General and administrative
Class Of Stock [Line Items]
Stock based compensation expense	$ 648	$ 848	$ 1,205

Stockholders' Equity - Summar_4

Stockholders' Equity - Summary of Common Stock Reserved For Future Issuance (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Jan. 02, 2015
Stock Plans
Shares of common stock reserved for future issuance	5,574,972	2,134,353
Number of shares, options vested and expected to vest	601,481	370,391
2015 Equity Incentive Plan
Stock Plans
Shares of common stock reserved for future issuance	57,468	128,589	80,103
Common Stock. | Warrants
Stock Plans
Shares of common stock reserved for future issuance	4,810,409	1,561,903
ESPP
Stock Plans
Shares of common stock reserved for future issuance			18,346
Shares of common stock reserved for future issuance	105,614	73,470

Collaborations - Additional Inf

Collaborations - Additional Information (Details)	1 Months Ended		12 Months Ended
	Feb. 01, 2021USD ($)	Nov. 30, 2018USD ($)antibody	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)	Mar. 31, 2020USD ($)
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contracts Revenue			$ 0	$ 0	$ 3,000,000
Type of Revenue [Extensible List]			tcon:CollaborationMember	tcon:CollaborationMember	tcon:CollaborationMember
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 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
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
Bispecific Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Royalty on net sales			50.00%
Bispecific Agreement | I-Mab
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum number of proprietary bispecific antibodies under development | antibody		5
Number of biological targets | antibody		2
Bispecific Agreement | I-Mab | North America
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Maximum period of selecting candidates for development and commercialization		5 years
Bispecific Agreement | I-Mab | 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
Bispecific Agreement | I-Mab | 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
Bispecific Agreement | I-Mab | 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
Bispecific Agreement | I-Mab | 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
Collaboration Agreements | I-Mab
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Consideration exchanged for assets acquired			$ 0
Value given to assets acquired			0
TJ4309 Agreement
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of cost bearing		40.00%
TJ4309 Agreement | I-Mab
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Percentage of cost bearing		60.00%
Potential payments receivable						$ 340,000
Termination of agreement upon completion of clinical study		90 days
Additional payment		$ 35,000,000
TJ4309 Agreement | I-Mab | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Non-royalty consideration		35,000,000
TJ4309 Agreement | I-Mab | First Phase Clinical Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination fee		9,000,000
TJ4309 Agreement | I-Mab | First Phase Two Clinical Study
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination fee		$ 15,000,000
TJ4309 Agreement | I-Mab | Subsequent Event
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Termination fee	$ 9,000,000
Collaborative Arrangement | Santen
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Contracts Revenue			$ 0	$ 0	$ 0
Type of Revenue [Extensible List]			tcon:CollaborationMember	tcon:CollaborationMember	tcon:CollaborationMember

Leases - Additional Information

Leases - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Non-cancelable operating lease expiration term	2022-04
Non-cancelable operating lease additional term to be extended	60 months
Operating lease expense	$ 400,000	$ 400,000	$ 400,000
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) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Leases [Abstract]
Cash paid within operating cash flows	$ 442	$ 423	$ 405

Leases - Supplemental balance s

Leases - Supplemental balance sheet information related to operating leases (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Reported as:
Current portion of operating lease liability	$ 570	$ 925
Weighted average remaining lease term	1 year 3 months 19 days	2 years 3 months 19 days
Weighted average discount rate	11.30%	11.30%
Other assets (ROU asset)
Reported as:
Other assets (ROU asset)	$ 508	$ 838
Accounts payable and accrued expenses (lease liability)
Reported as:
Current portion of operating lease liability	418	355
Other long-term liabilities (lease liability)
Reported as:
Current portion of operating lease liability	$ 152	$ 570

Leases - Schedule of Maturities

Leases - Schedule of Maturities of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Operating lease liabilities payments due
2021	$ 461
2022	156
Total lease payments	617
Less imputed interest	(47)
Total operating lease liabilities	$ 570	$ 925

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Effective Tax Rate and Federal Statutory Tax Rate (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Reconciliation of effective tax rate and federal statutory tax rate
Federal income taxes	$ (3,523)	$ (4,761)	$ (7,341)
State income taxes, net of federal benefit	(1,084)	(1,381)	(2,340)
Permanent items	104	149	439
Uncertain tax positions	1,224	1,828	672
Research and development credits	(555)	(1,253)	(2,545)
Rate change			629
Other, net		(75)
Stock compensation	113	395	66
Change in valuation allowance	3,721	5,098	10,420
Provision for income taxes	$ 0	$ 0	$ 0

Income Taxes - Schedule of Comp

Income Taxes - Schedule of Components of deferred tax assets and deferred tax Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Deferred tax assets:
Net operating loss carryforwards	$ 40,103	$ 36,850
Research and development credits and Orphan Drug Credit	9,321	8,944
Depreciation and amortization	258	269
Right-of-use liability	120	194
Other, net	1,476	1,369
Total deferred tax assets	51,278	47,626
Right-of-use asset	(107)	(176)
Total deferred tax liabilities	(107)	(176)
Total net deferred	51,171	47,450
Valuation allowance	(51,171)	(47,450)
Net deferred tax assets	$ 0	$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Carryforwards
Net change in the total valuation allowance	$ 3,700,000	$ 5,100,000	$ 10,400,000
Accrual for interest or penalties for unrecognized tax benefits	0	0
Income tax interest or penalties expense for unrecognized tax benefits	$ 0	$ 3
Minimum
Carryforwards
Percent of ownership	50.00%		50.00%
CARES Act
Carryforwards
NOL carryforward available to offset future taxable income, percentage	80.00%	80.00%	80.00%
Federal
Carryforwards
NOL carryforward	$ 152,500,000
NOL carryforward begin to expire	2030
Federal | Research and Development and Orphan Drug Credit Carryforwards
Carryforwards
Credit carryforward	$ 10,300,000
Credit carryforward begin to expire	2031
California
Carryforwards
NOL carryforward	$ 117,700,000
NOL carryforward begin to expire	2030
California | Research and Development and Orphan Drug Credit Carryforwards
Carryforwards
Credit carryforward	$ 2,500,000

Income Taxes - Schedule of Chan

Income Taxes - Schedule of Changes in Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Unrecognized tax benefits
Balance, beginning of period	$ 5,092	$ 2,859	$ 2,166
Increase related to current year positions	1,518	2,233	693
Balance, end of period	$ 6,610	$ 5,092	$ 2,859

401(k) Plan - Additional Inform

401(k) Plan - Additional Information (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Defined Contribution Pension and Other Postretirement Plans Disclosure
Defined contribution, plan name	tcon:FourZeroOneKMember
Defined contribution amount	$ 0.1	$ 0.2	$ 0.2