0000950170-22-001967 | 10-K | XBRL Viewer

Description of Business	12 Months Ended
Dec. 31, 2021
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Description of Business	1. Description of Business Kura Oncology, Inc., is a clinical-stage biopharmaceutical company committed to realizing the promise of precision medicines for the treatment of cancer. Our pipeline consists of small molecule product candidates that target cancer signaling pathways where there is a strong scientific and clinical rationale to improve outcomes, and we intend to pair them with molecular or cellular diagnostics to identify those patients most likely to respond to treatment. We plan to advance our product candidates through a combination of internal development and strategic partnerships while maintaining significant development and commercial rights. References in these Notes to Financial Statements to “Kura Oncology, Inc.,” “we,” “our” or “us,” refer to Kura Oncology, Inc.

Description of Business

12 Months Ended

Dec. 31, 2021

Organization Consolidation And Presentation Of Financial Statements [Abstract]

1. Description of Business

Kura Oncology, Inc., is a clinical-stage biopharmaceutical company committed to realizing the promise of precision medicines for the treatment of cancer. Our pipeline consists of small molecule product candidates that target cancer signaling pathways where there is a strong scientific and clinical rationale to improve outcomes, and we intend to pair them with molecular or cellular diagnostics to identify those patients most likely to respond to treatment. We plan to advance our product candidates through a combination of internal development and strategic partnerships while maintaining significant development and commercial rights.

References in these Notes to Financial Statements to “Kura Oncology, Inc.,” “we,” “our” or “us,” refer to Kura Oncology, Inc.

STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Activities
Net loss	$ (130,466)	$ (89,625)	$ (63,140)
Adjustments to reconcile net loss to net cash used in operating activities:
Share-based compensation expense	23,579	12,807	9,409
Non-cash interest expense	399
Loss from extinguishment of debt	212
Depreciation expense	558	194
Amortization of premium and accretion of discounts on marketable securities, net	4,391	410	(1,103)
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(357)	(711)	(875)
Other long-term assets	(329)	1,205	(117)
Accounts payable and accrued expenses	(2,518)	5,677	856
Other long-term liabilities	(20)	213	210
Net cash used in operating activities	(104,551)	(69,830)	(54,760)
Investing Activities
Purchases of marketable securities	(445,657)	(320,963)	(227,571)
Maturities of marketable securities	319,969	223,198	181,246
Purchases of property and equipment	(1,147)	(2,171)
Net cash used in investing activities	(126,835)	(99,936)	(46,325)
Financing Activities
Repayment of long-term debt	(7,250)	(250)
Payment of fees related to extinguishment of debt	(611)
Proceeds from exercises of stock options and purchases under employee stock purchase plan	4,426	10,249	2,936
Proceeds from issuances of common stock, net		459,335	108,165
Net cash (used in) provided by financing activities	(3,435)	469,334	111,101
Net (decrease) increase in cash, cash equivalents and restricted cash	(234,821)	299,568	10,016
Cash, cash equivalents and restricted cash at beginning of period	325,703	26,135	16,119
Cash, cash equivalents and restricted cash at end of period	90,882	325,703	26,135
Supplemental disclosure of cash flow information:
Interest paid	$ 784	$ 419	$ 430

Share-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Summary of Stock Option Activities

The exercise price of all stock options granted was equal to the fair market value of such stock on the date of grant. Stock options generally vest over a four-year period. The maximum contractual term for all stock options is ten years. The following is a summary of stock option activity for the year ended December 31, 2021, in thousands (except per share and years data):


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		5,021		$	15.37
Granted		2,835		$	27.70
Exercised		(343	)	$	11.11
Canceled		(562	)	$	21.94
Outstanding at December 31, 2021		6,951		$	20.08		7.9	$	5,565
Vested and expected to vest at December 31, 2021		6,951		$	20.08		7.9	$	5,565
Exercisable at December 31, 2021		3,145		$	16.93		6.9	$	4,152

Summary of Information Regarding Stock Options

The following summarizes certain information regarding stock options, in thousands (except per share data):


	Years Ended December 31,
	2021		2020		2019
Cash received from options exercised	$	3,809	$	9,766	$	2,562
Intrinsic value of options exercised	$	3,475	$	13,348	$	4,311
Weighted-average grant date fair value per share	$	17.84	$	10.15	$	10.93

Summary of RSU Activity

The following is a summary of RSU activity for the year ended December 31, 2021, in thousands (except per share and years data):


	Number of RSUs			Weighted Average Grant Date Fair Value per Share		Weighted Average Remaining Vesting Period (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		—		$	—
Granted		187		$	32.80
Released		—		$	—
Canceled		(26	)	$	32.80
Outstanding at December 31, 2021		161		$	32.80		1.6	$	2,261
Expected to vest at December 31, 2021		161		$	32.80		1.6	$	2,261

Summary of Share-based Compensation Expense

Total share-based compensation expense included on the statements of operations and comprehensive loss was comprised of the following, in thousands:


	Years Ended December 31,
	2021		2020		2019
Research and development	$	7,454	$	3,960	$	3,427
General and administrative		16,125		8,847		5,982
Total share-based compensation expense	$	23,579	$	12,807	$	9,409

Summary of Estimate Fair Value of Employee Stock Options and ESPP Using Black-Scholes Model

We estimated the fair value of employee stock options and ESPP using the Black-Scholes model based on the date of grant with the following assumptions:


	Options						ESPP
	Years Ended December 31,						Years Ended December 31,
	2021		2020		2019		2021		2020		2019
Expected term (in years)	5.50 — 6.08		5.50 — 6.08		5.50 — 6.08			0.50		0.50		0.50
Expected volatility	72.0% — 74.6%		74.4% — 76.1%		73.1% — 77.2%		44.8% — 61.8%		55.3% — 91.9%		43.9% — 54.2%
Risk-free interest rate	0.6% — 1.3%		0.4% — 2.0%		2.1% — 2.8%		0.0%— 0.1%		0.1% — 0.9%		1.9% — 2.5%
Expected dividend yield		—		—		—		—		—		—

Income Taxes - Schedule of Effective Income Tax Rate Reconciliation (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income taxes at statutory federal rate	$ (27,398,000)	$ (18,821,000)	$ (13,259,000)
State income tax, net of federal benefit	(9,758,000)	(7,684,000)	(4,810,000)
Research and development tax credits	(5,850,000)	(3,169,000)	(1,664,000)
Share-based compensation	2,819,000	(304,000)	708,000
Other	(496,000)	(120,000)	199,000
Valuation allowance	40,683,000	30,098,000	18,826,000
Income tax expense	$ 0	$ 0	$ 0

- Definition

Amount of current income tax expense (benefit) and deferred income tax expense (benefit) pertaining to continuing operations.

+ References + Details

Summary of Significant Accounting Policies - Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Accounting Policies [Abstract]
Cash and cash equivalents	$ 90,672	$ 325,493	$ 26,135
Restricted cash	210	210
Total	$ 90,882	$ 325,703	$ 26,135	$ 16,119

Stockholder's Equity - Additional Information (Detail) - USD ($)	1 Months Ended				12 Months Ended
	Dec. 31, 2020	May 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stockholders' Equity Note [Abstract]
Common stock, shares issued	9,326,500	10,465,000	6,785,000
Common stock, issued price per share	$ 37.00	$ 13.75	$ 17.00			$ 37.00
Proceeds from issuance of common stock, net	$ 324,100,000	$ 134,900,000	$ 108,100,000			$ 459,335,000	$ 108,165,000
ATM Facility
Stockholders' Equity Note [Abstract]
Common stock, shares issued					0
ATM Facility \| Maximum
Stockholders' Equity Note [Abstract]
Aggregate offering price				$ 75,000,000.0
Term Loan \| Oxford Finance LLC and Silicon Valley Bank
Stockholders' Equity Note [Abstract]
Warrants issued to purchase of common stock					33,988
Warrants exercisable exercise price					$ 3.31

Balance Sheet Detail (Tables)

12 Months Ended

Dec. 31, 2021

Balance Sheet Related Disclosures [Abstract]

Summary of Property and Equipment

Property and equipment consisted of the following, in thousands:


	December 31,
	2021			2020
Leasehold improvements	$	1,532		$	1,169
Furniture and fixtures		1,032			862
Laboratory and computer equipment		953			276
Property and equipment, gross		3,517			2,307
Less: accumulated depreciation		(844	)		(286	)
Property and equipment, net	$	2,673		$	2,021

Summary of Accounts Payable and Accrued Expenses

Accounts payable and accrued expenses consisted of the following, in thousands:


	December 31,
	2021		2020
Accounts payable	$	3,236	$	2,753
Accrued clinical trial research and development expenses		2,619		4,080
Accrued other research and development expenses		5,341		5,581
Accrued compensation and benefits		7,923		7,016
Operating lease liability, current portion		2,263		2,089
Other accrued expenses		1,073		1,505
Total accounts payable and accrued expenses	$	22,455	$	23,024

Commitments and Contingencies - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) Lease	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)
Loss Contingencies [Line Items]
Number of operating leases \| Lease	3
Lessee, operating lease, expiration period	We currently have three operating leases for administrative and research and development office and lab space in San Diego, California and Boston, Massachusetts that expire between July 2024 and November 2025.
Number of leases that include renewal option \| Lease	2
Lease agreement additional extended lease term	5 years
Operating lease right-of-use assets	$ 5,573	$ 6,334
Operating leases, liability	6,875	7,700
Long-term operating lease liabilities	$ 4,612	$ 5,638
Weighted-average discount rate	5.50%	5.50%
Weighted-average remaining lease term	3 years 3 months 18 days	4 years 1 month 6 days
Total cash paid for amounts included in the measurement of lease liabilities	$ 2,100	$ 300	$ 500
ROU assets obtained in exchange for operating lease liabilities	1,000	7,500	700
Total operating lease rent expense	2,000	2,000	600
ASC 842
Loss Contingencies [Line Items]
Total operating lease rent expense	2,000	$ 1,700	$ 500
San Diego Corporate Headquarters Lease
Loss Contingencies [Line Items]
Lease allowance	1,000
Office Lease in Boston \| Letter of Credit
Loss Contingencies [Line Items]
Letter of Credit	200
San Diego Lease for Lab and Office Space
Loss Contingencies [Line Items]
Lease allowance	$ 100

Balance Sheet Detail - Summary of Accounts Payable and Accrued Expenses (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Payables And Accruals [Abstract]
Accounts payable	$ 3,236	$ 2,753
Accrued clinical trial research and development expenses	2,619	4,080
Accrued other research and development expenses	5,341	5,581
Accrued compensation and benefits	7,923	7,016
Operating lease liability, current portion	$ 2,263	$ 2,089
Operating Lease, Liability, Current, Statement of Financial Position [Extensible Enumeration]	Total accounts payable and accrued expenses	Total accounts payable and accrued expenses
Other accrued expenses	$ 1,073	$ 1,505
Total accounts payable and accrued expenses	$ 22,455	$ 23,024

Fair Value Measurements

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Fair Value Measurements

4. Fair Value Measurements

As of December 31, 2021 and 2020, we had cash equivalents and short-term investments measured at fair value on a recurring basis.

Available-for-sale securities consist of U.S. Treasury securities, which are measured at fair value using Level 1 inputs, and corporate debt securities, commercial paper, non-U.S. government debt securities, supranational debt securities and U.S. Agency bonds which are measured at fair value using Level 2 inputs. We determine the fair value of Level 2 related securities with the aid of valuations provided by third parties using proprietary valuation models and analytical tools. These valuation models and analytical tools use market pricing or prices for similar instruments that are both objective and publicly available, including matrix pricing or reported trades, benchmark yields, broker/dealer quotes, issuer spreads, two-sided markets, benchmark securities, bids and/or offers. We validate the fair values of Level 2 financial instruments by comparing these fair values to a third-party pricing source.

The following tables summarize, by major security type, our cash equivalents and short-term investments that are measured at fair value on a recurring basis and are categorized using the fair value hierarchy, in thousands:


	December 31, 2021
	Total		Level 1		Level 2
Cash equivalents:
Money market funds	$	79,895	$	79,895	$	—

Short-term investments:
Corporate debt securities		207,172		—		207,172
U.S. Treasury securities		134,833		134,833		—
Commercial paper		53,439		—		53,439
Non-U.S. government and supranational debt securities		22,908		—		22,908
U.S. Agency bonds		8,936		—		8,936
Total short-term investments		427,288		134,833		292,455
Total	$	507,183	$	214,728	$	292,455


	December 31, 2020
	Total		Level 1		Level 2
Cash equivalents:
Money market funds	$	311,239	$	311,239	$	—
Commercial paper		5,998		—		5,998
Total cash equivalents		317,237		311,239		5,998

Short-term investments:
Corporate debt securities		113,020		—		113,020
U.S. Treasury securities		88,457		88,457		—
Commercial paper		106,350		—		106,350
Total short-term investments		307,827		88,457		219,370
Total	$	625,064	$	399,696	$	225,368

Related Party Transactions - Additional Information (Detail) - USD ($)			12 Months Ended			37 Months Ended
	Jan. 01, 2020	Oct. 01, 2014	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Jun. 30, 2020	Dec. 23, 2014
Related Party Transaction [Line Items]
Rent expense related to office space sublease			$ 2,000,000.0	$ 2,000,000.0	$ 600,000
Milestone paid to date			$ 100,000
Araxes Pharma LLC \| San Diego, California
Related Party Transaction [Line Items]
Sublease term			We subleased office space in San Diego, California from Araxes between June 2017 and June 2020.
Rent expense related to office space sublease				200,000	400,000
Araxes Pharma LLC \| Monthly \| San Diego, California \| Minimum
Related Party Transaction [Line Items]
Rent expense, amended sublease						$ 16,000
Araxes Pharma LLC \| Monthly \| San Diego, California \| Maximum
Related Party Transaction [Line Items]
Rent expense, amended sublease						$ 24,000
Araxes Pharma LLC \| Management Fees
Related Party Transaction [Line Items]
Research and development services reimbursement, description			In addition, the agreement allows for Araxes to reimburse us an amount equal to the number of full-time equivalents, or FTE, performing research and development services for Araxes, at an annual FTE rate of approximately $382,000, plus actual expenses as reasonably incurred.
Management fee income, related party			$ 100,000	100,000	200,000
Service Agreement for research and development	$ 382,000
Reimbursements of research and development services			$ 0		100,000
Wellspring Biosciences Inc \| Service Agreements
Related Party Transaction [Line Items]
Research and development services expense at full time equivalents rate		$ 400,000
Research and development expense payment, description			We have a services agreement with Wellspring Biosciences, Inc., or Wellspring, a wholly-owned subsidiary of Araxes, pursuant to which we pay Wellspring for research and development services provided to us in an amount equal to the number of FTE’s performing the services, at an annual FTE rate of $400,000, plus actual expenses as reasonably incurred. For the year ended December 31, 2021, we did not recognize any expense under this service agreement.
Research and development, related party				100,000	200,000
ALG Partners, LLC \| Service Agreements
Related Party Transaction [Line Items]
Research and development, related party			$ 0	100,000	100,000
Araxes Asset Purchase Agreement
Related Party Transaction [Line Items]
Convertible notes payable							$ 500,000
Contingent Milestone Payables							$ 9,700,000
Milestone payments paid to date			300,000
Milestone paid to date			$ 0	$ 0	$ 0

STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid- In Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2018	$ 160,985	$ 4	$ 310,849	$ (131)	$ (149,737)
Beginning balance (in shares) at Dec. 31, 2018		38,148
Issuance of common stock, net of offering costs	108,129	$ 1	108,128
Issuance of common stock, net of offering costs, (in shares)		6,785
Share-based compensation expense	9,409		9,409
Issuance of common stock from exercise of options and employee stock purchase plan	2,936		2,936
Issuance of common stock from exercise of options and employee stock purchase plan (in shares)		451
Other comprehensive income (loss)	462			462
Net loss	(63,140)				(63,140)
Ending balance at Dec. 31, 2019	218,781	$ 5	431,322	331	(212,877)
Ending balance (in shares) at Dec. 31, 2019		45,384
Issuance of common stock, net of offering costs	458,978	$ 2	458,976
Issuance of common stock, net of offering costs, (in shares)		19,792
Share-based compensation expense	12,807		12,807
Issuance of common stock from exercise of options and employee stock purchase plan	10,249		10,249
Issuance of common stock from exercise of options and employee stock purchase plan (in shares)		1,018
Other comprehensive income (loss)	(285)			(285)
Net loss	(89,625)				(89,625)
Ending balance at Dec. 31, 2020	610,905	$ 7	913,354	46	(302,502)
Ending balance (in shares) at Dec. 31, 2020		66,194
Share-based compensation expense	23,579		23,579
Issuance of common stock from exercise of options and employee stock purchase plan	4,426		4,426
Issuance of common stock from exercise of options and employee stock purchase plan (in shares)		378
Other comprehensive income (loss)	(1,835)			(1,835)
Net loss	(130,466)				(130,466)
Ending balance at Dec. 31, 2021	$ 506,609	$ 7	$ 941,359	$ (1,789)	$ (432,968)
Ending balance (in shares) at Dec. 31, 2021		66,572

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

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Amount after tax and reclassification adjustments of other comprehensive income (loss).

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Total of all stockholders' equity (deficit) items, net of receivables from officers, directors, owners, and affiliates of the entity which are attributable to the parent. The amount of the economic entity's stockholders' equity attributable to the parent excludes the amount of stockholders' equity which is allocable to that ownership interest in subsidiary equity which is not attributable to the parent (noncontrolling interest, minority interest). This excludes temporary equity and is sometimes called permanent equity.

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+ Details

Balance Sheet Detail - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Balance Sheet Related Disclosures [Abstract]
Depreciation expense	$ 558	$ 194

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Schedule of Effective Income Tax Rate Reconciliation

Our effective income tax rate differs from the statutory federal rate of 21% for the years ended December 31, 2021, 2020 and 2019, due to the following, in thousands:


	Years Ended December 31,
	2021			2020			2019
Income taxes at statutory federal rate	$	(27,398	)	$	(18,821	)	$	(13,259	)
State income tax, net of federal benefit		(9,758	)		(7,684	)		(4,810	)
Research and development tax credits		(5,850	)		(3,169	)		(1,664	)
Share-based compensation		2,819			(304	)		708
Other		(496	)		(120	)		199
Valuation allowance		40,683			30,098			18,826
Income tax expense	$	—		$	—		$	—

Components of Deferred Tax Assets and Liabilities

Significant components of our deferred tax assets and liabilities are shown below, in thousands:


	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	111,238		$	79,230
Research and development tax credit carryforwards		13,794			7,944
Share-based compensation		4,842			2,638
Operating lease liabilities		2,021			2,278
Accruals		2,096			1,915
Other		1,088			641
Total gross deferred tax assets		135,079			94,646
Less valuation allowance		(133,206	)		(92,523	)
Net deferred tax assets		1,873			2,123
Deferred tax liabilities:
Operating lease right-of-use assets		(1,638	)		(1,868	)
Other		(235	)		(255	)
Total gross deferred tax liabilities		(1,873	)		(2,123	)
Net deferred tax assets	$	—		$	—

Schedule of Activity Related to Unrecognized Tax Benefits

The following table summarizes the activity related to our unrecognized tax benefits, in thousands:


	December 31,
	2021		2020		2019
Gross unrecognized tax benefits at the beginning of the year	$	2,978	$	1,741	$	1,063
Increases related to prior year tax positions		—		—		—
Increases from tax positions taken in the current year		1,424		1,237		678
Gross unrecognized tax benefits at the end of the year	$	4,402	$	2,978	$	1,741

Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2021

Fair Value Disclosures [Abstract]

Schedule Of Fair Value Measurements, By Major Security Type


	December 31, 2021
	Total		Level 1		Level 2
Cash equivalents:
Money market funds	$	79,895	$	79,895	$	—

Short-term investments:
Corporate debt securities		207,172		—		207,172
U.S. Treasury securities		134,833		134,833		—
Commercial paper		53,439		—		53,439
Non-U.S. government and supranational debt securities		22,908		—		22,908
U.S. Agency bonds		8,936		—		8,936
Total short-term investments		427,288		134,833		292,455
Total	$	507,183	$	214,728	$	292,455


	December 31, 2020
	Total		Level 1		Level 2
Cash equivalents:
Money market funds	$	311,239	$	311,239	$	—
Commercial paper		5,998		—		5,998
Total cash equivalents		317,237		311,239		5,998

Short-term investments:
Corporate debt securities		113,020		—		113,020
U.S. Treasury securities		88,457		88,457		—
Commercial paper		106,350		—		106,350
Total short-term investments		307,827		88,457		219,370
Total	$	625,064	$	399,696	$	225,368

Share-Based Compensation - Summary of RSU Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Restricted Stock Units Outstanding, Beginning Balance, Number of Shares \| shares	0
Granted, Number of Shares \| shares	187
Canceled, Number of Shares \| shares	(26)
Restricted Stock Units Outstanding, Ending Balance, Number of Shares \| shares	161
Expected to vest, Number of Shares \| shares	161
Outstanding, Beginning Balance, Weighted Average Grant Date Fair Value per Share \| $ / shares	$ 0
Granted, Weighted Average Grant Date Fair Value per Share \| $ / shares	32.80
Canceled, Weighted Average Grant Date Fair Value per Share \| $ / shares	32.80
Outstanding, Ending Balance, Weighted Average Grant Date Fair Value per Share \| $ / shares	32.80
Expected to Vest, Weighted Average Grant Date Fair Value per Share \| $ / shares	$ 32.80
Outstanding, Ending Balance, Weighted Average Remaining Vesting Period (years)	1 year 7 months 6 days
Expected to vest, Weighted Average Remaining Vesting Period (years)	1 year 7 months 6 days
Outstanding, Ending Balance, Aggregate Intrinsic Value \| $	$ 2,261
Expected to Vest, Aggregate Intrinsic Value \| $	$ 2,261

License Agreements - Additional Information (Detail) - USD ($)			12 Months Ended
	Dec. 22, 2014	Dec. 18, 2014	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	$ 80,200,000
Milestone paid to date			$ 100,000
The University of Michigan License Agreement
License Agreements [Line Items]
License agreement date	Dec. 22, 2014
Agreement termination written notice	90 days
Agreement termination notice period in event of material breach	60 days
Agreement termination period due to payment failure	30 days
Janssen License Agreement
License Agreements [Line Items]
License agreement date		Dec. 22, 2014
Agreement termination written notice		180 days
Agreement termination notice period in event of material breach		45 days
Janssen License Agreement \| Up front Payment Arrangement
License Agreements [Line Items]
Upfront license fee		$ 1,000,000.0
Initiation of Certain Development Activities
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	$ 500,000
Specified Regulatory Approvals
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	28,900,000
Specified Levels of Product Sales
License Agreements [Line Items]
Total future milestone payments under license agreements with non-related parties	$ 50,800,000
Araxes Asset Purchase Agreement
License Agreements [Line Items]
Milestone paid to date			$ 0	$ 0	$ 0

Income Taxes

12 Months Ended

Dec. 31, 2021

Income Tax Disclosure [Abstract]

Income Taxes

13. Income Taxes

For the years ended December 31, 2021, 2020 and 2019, we did not record a provision for income taxes due to a full valuation against our deferred taxes.

Our effective income tax rate differs from the statutory federal rate of 21% for the years ended December 31, 2021, 2020 and 2019, due to the following, in thousands:


	Years Ended December 31,
	2021			2020			2019
Income taxes at statutory federal rate	$	(27,398	)	$	(18,821	)	$	(13,259	)
State income tax, net of federal benefit		(9,758	)		(7,684	)		(4,810	)
Research and development tax credits		(5,850	)		(3,169	)		(1,664	)
Share-based compensation		2,819			(304	)		708
Other		(496	)		(120	)		199
Valuation allowance		40,683			30,098			18,826
Income tax expense	$	—		$	—		$	—

Significant components of our deferred tax assets and liabilities are shown below, in thousands:


	December 31,
	2021			2020
Deferred tax assets:
Net operating loss carryforwards	$	111,238		$	79,230
Research and development tax credit carryforwards		13,794			7,944
Share-based compensation		4,842			2,638
Operating lease liabilities		2,021			2,278
Accruals		2,096			1,915
Other		1,088			641
Total gross deferred tax assets		135,079			94,646
Less valuation allowance		(133,206	)		(92,523	)
Net deferred tax assets		1,873			2,123
Deferred tax liabilities:
Operating lease right-of-use assets		(1,638	)		(1,868	)
Other		(235	)		(255	)
Total gross deferred tax liabilities		(1,873	)		(2,123	)
Net deferred tax assets	$	—		$	—

As of December 31, 2021, we had federal net operating loss, or NOL, carryforwards of $380.5 million, of which $305.1 million can be carried forward indefinitely. The remaining federal net operating loss carryforwards of $75.4 million will begin to expire in 2034, unless previously utilized. In addition, as of December 31, 2021, we had state loss carryforwards of $456.5 million, of which $456.0 million begin to expire in 2034 and $0.5 million begin to expire in 2030, unless previously utilized. We also have federal and state research and development credit carryforwards of $14.6 million and $4.0 million, respectively, as of December 31, 2021. The federal research and development credits will begin to expire in 2034, unless previously utilized. Of the state research and development credits, $2.4 million will carryforward indefinitely and approximately $1.6 million will begin to expire in 2031, unless previously utilized.

We file tax returns as prescribed by the tax laws of the jurisdictions in which we operate. Our tax years since inception are subject to examination by the federal and state jurisdictions due to the carryforward of unutilized net operating losses and research and development credits. We have not been, nor are we currently, under examination by the federal or any state tax authority.

Management assesses the available positive and negative evidence to estimate if sufficient future taxable income will be generated to use existing deferred tax assets. Based on the weight of the evidence, including our limited existence and losses since inception, management has determined that it is more likely than not that the deferred tax assets will not be realized and therefore has recorded a full valuation allowance against the deferred taxes. The valuation allowance increased by $40.7 million from December 31, 2020.

Pursuant to Sections 382 and 383 of the Internal Revenue Code, or IRC, annual use of our NOL or research and development credit carryforwards may be limited in the event a cumulative change in ownership of more than 50% occurs within a three-year period. We previously completed a study to assess whether an ownership change, as defined by IRC Section 382, had occurred from our formation through March 31, 2016. Based upon this study, we determined that an ownership change occurred but concluded the annual utilization limitation would be sufficient to utilize our pre-ownership change NOLs and research and development credits prior to expiration. We completed additional studies and concluded no further ownership changes occurred through December 31, 2018. We are currently in the process of completing a study for 2019, 2020, and 2021, however, we do not expect any material limitations to the utilization of NOLs or research and development credits. Future ownership changes may limit our ability to utilize remaining tax attributes. Any carryforwards that will expire prior to utilization as a result of such additional limitations will be removed from deferred tax assets, with a corresponding reduction of the valuation allowance.

In accordance with authoritative guidance, the impact of an uncertain income tax position is recognized at the largest amount that is “more likely than not” to be sustained upon audit by the relevant taxing authority. An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained.

The following table summarizes the activity related to our unrecognized tax benefits, in thousands:


	December 31,
	2021		2020		2019
Gross unrecognized tax benefits at the beginning of the year	$	2,978	$	1,741	$	1,063
Increases related to prior year tax positions		—		—		—
Increases from tax positions taken in the current year		1,424		1,237		678
Gross unrecognized tax benefits at the end of the year	$	4,402	$	2,978	$	1,741

Our practice is to recognize interest and penalties related to income tax matters in income tax expense. There was no accrued interest or penalties included on the balance sheets as of December 31, 2021 and 2020, and we have not recognized interest and penalties on the statements of operations and comprehensive loss for the years ended December 31, 2021, 2020 or 2019.

We do not expect that there will be a significant change in the unrecognized tax benefits over the next 12 months. Due to the existence of the valuation allowance, future changes in our unrecognized tax benefits will not impact our effective tax rate.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

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-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(h)(2))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

+ Details

Investments

12 Months Ended

Dec. 31, 2021

Investments All Other Investments [Abstract]

Investments

. Investments

We invest in available-for-sale securities consisting of money market funds, corporate debt securities, U.S. Treasury securities, commercial paper, non-U.S. government debt securities, supranational debt securities and U.S. Agency bonds. Available-for-sale securities are classified as either cash and cash equivalents or short-term investments on the balance sheets.

The following tables summarize, by major security type, our short-term investments that are measured at fair value on a recurring basis, in thousands:


		December 31, 2021
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	1 or less	$	79,895	$	—	$	—		$	79,895

Short-term investments:
Corporate debt securities	3 or less		208,064		—		(892	)		207,172
U.S. Treasury securities	3 or less		135,452		—		(619	)		134,833
Commercial paper	1 or less		53,439		—		—			53,439
Non-U.S. government and supranational debt securities	3 or less		23,122		—		(214	)		22,908
U.S. Agency bonds	2 or less		8,994		—		(58	)		8,936
Total short-term investments			429,071		—		(1,783	)		427,288
Total		$	508,966	$	—	$	(1,783	)	$	507,183


		December 31, 2020
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	1 or less	$	311,239	$	—	$	—		$	311,239
Commercial paper	1 or less		5,998		—		—			5,998
Total cash equivalents			317,237		—		—			317,237

Short-term investments:
Corporate debt securities	2 or less		113,020		36		(36	)		113,020
U.S. Treasury securities	1 or less		88,409		50		(2	)		88,457
Commercial paper	1 or less		106,350		—		—			106,350
Total short-term investments			307,779		86		(38	)		307,827
Total		$	625,016	$	86	$	(38	)	$	625,064

Short-term investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. As of December 31, 2021 and 2020, short-term investments of $246.9 million and $242.6 million, respectively, had maturities less than one year, and short-term investments of $180.4 million and $65.2 million, respectively, had maturities between one to three years. Realized gains and losses were de minimis for the years ended December 31, 2021, 2020 and 2019.

As of December 31, 2021 and 2020, 36 available-for-sale securities with a fair market value of $373.9 million and 10 available-for-sale securities with a fair market value of $85.2 million, respectively, were in gross unrealized loss positions, none of which were in a continuous unrealized loss position for greater than 12 months. We do not intend to sell these available-for-sale securities, and it is not more likely than not that we will be required to sell these securities prior to recovery of their amortized cost basis. Based on our review of these available-for-sale securities, the unrealized losses at December 31, 2021 were primarily due to changes in interest rates and not due to increased credit risks associated with specific securities. We have no allowance for credit losses as of December 31, 2021 and 2020. Unrealized gains and losses that are not credit-related are included in accumulated other comprehensive income (loss).

Accrued interest receivable on available-for-sale securities were $1.4 million and $0.9 million at December 31, 2021 and 2020, respectively. We have not written off any accrued interest receivables for the years ended December 31, 2021, 2020 and 2019.

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Schedule of Maturities of Lease Liabilities

Maturities of our lease liabilities as of December 31, 2021 are as follows, in thousands:


Year Ending December 31,
2022	$	2,319
2023		2,375
2024		1,863
2025		929
Total lease payments		7,486
Less: imputed interest		(611	)
Total operating lease liabilities	$	6,875

Investments - Additional Information (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) Security	Dec. 31, 2020 USD ($) Security
Investments All Other Investments [Abstract]
Short-term investments with maturities less than one year	$ 246,900	$ 242,600
Short-term investments with maturities between one to three years	$ 180,400	$ 65,200
Short-term investments maturities, description	As of December 31, 2021 and 2020, short-term investments of $246.9 million and $242.6 million, respectively, had maturities less than one year, and short-term investments of $180.4 million and $65.2 million, respectively, had maturities between one to three years.
Number of available-for-sale securities \| Security	36	10
Allowance for credit losses	$ 0	$ 0
Available for sale debt securities gross unrealized loss positions for less than twelve months	373,900	85,200
Accrued interest receivable on available-for-sale securities	$ 1,400	$ 900

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Provision for income taxes	$ 0	$ 0	$ 0
Effective federal statutory income tax rate, percent	21.00%	21.00%	21.00%
Increase in valuation allowance	$ 40,700,000
Deferred tax assets, valuation allowance	$ 133,206,000	$ 92,523,000
Income tax examination, likelihood of unfavorable settlement	An uncertain tax position will not be recognized if it has less than a 50% likelihood of being sustained.
Unrecognized interest and penalties	$ 0	$ 0	$ 0
Domestic Tax Authority
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 380,500,000
Loss carryforwards begin to expire	2034
Research and development credit carryforwards	$ 14,600,000
Credit carry forward begin to expire	2034
Domestic Tax Authority \| Not Subject to Expiration
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 305,100,000
Domestic Tax Authority \| Begin to Expire in 2034
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	75,400,000
State and Local Jurisdiction
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	456,500,000
Research and development credit carryforwards	4,000,000.0
State and Local Jurisdiction \| Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carryforwards not subject to expiration	2,400,000
State and Local Jurisdiction \| Begin to Expire in 2034
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 456,000,000.0
Loss carryforwards begin to expire	2034
State and Local Jurisdiction \| Begin to Expire in 2030
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Net operating loss carryforrwards	$ 500,000
Loss carryforwards begin to expire	2030
State and Local Jurisdiction \| Begin to Expire in 2031 \| Research and Development Credits
Significant Components Of Deferred Tax Assets And Liabilities [Line Items]
Credit carry forward begin to expire	2031
Credit carryforwards subject to expiration	$ 1,600,000

Commitments and Contingencies

12 Months Ended

Dec. 31, 2021

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

8. Commitments and Contingencies

Operating Leases

We currently have three operating leases for administrative and research and development office and lab space in San Diego, California and Boston, Massachusetts that expire between July 2024 and November 2025. Under the terms of the operating leases, we are required to pay our proportionate share of property taxes, insurance and normal maintenance costs. Two of our leases include renewal options for an additional five years, which were not included in the determination of the ROU asset or lease liability as the renewal was not reasonably certain at the inception of the lease. Our San Diego corporate headquarters lease and our San Diego lease for lab and office space provided for $1.0 million and $0.1 million, respectively, in reimbursements for allowable tenant improvements, which effectively reduced the total lease payments owed. Under the terms of our office lease in Boston, we are required to maintain a standby letter of credit of approximately $0.2 million during the term of the lease. Additionally, we had other operating leases including a sublease with a related party for office space in San Diego, California and a lease for office space in Cambridge, Massachusetts that ended in 2020, and a sublease for lab space in San Diego that ended in August 2021.

Maturities of our lease liabilities as of December 31, 2021 are as follows, in thousands:


Year Ending December 31,
2022	$	2,319
2023		2,375
2024		1,863
2025		929
Total lease payments		7,486
Less: imputed interest		(611	)
Total operating lease liabilities	$	6,875

As of December 31, 2021 and 2020, total operating lease ROU assets were $5.6 million and $6.3 million, respectively. As of December 31, 2021, total operating lease liabilities were $6.9 million, of which $4.6 million were recorded as long-term lease liabilities. As of December 31, 2020, total operating lease liabilities were $7.7 million, of which $5.6 million were

recorded as long-term lease liabilities. As of December 31, 2021 and 2020, the weighted-average discount rate was 5.5% for both periods, and the weighted-average remaining lease term was 3.3 years and 4.1 years, respectively.

Total cash paid for amounts included in the measurement of operating lease liabilities, net of tenant improvement reimbursements, was $2.1 million, $0.3 million and $0.5 million for the years ended December 31, 2021, 2020 and 2019, respectively. Operating lease ROU assets obtained in exchange for operating lease liabilities were $1.0 million, $7.5 million and $0.7 million for the years ended December 31, 2021, 2020 and 2019, respectively.

Total operating lease expense was approximately $2.0 million, $1.7 million and $0.5 million for the years ended December 31, 2021, 2020 and 2019, respectively. We had also entered into short-term operating leases that expired in 2020. Total rent expense for the years ended December 31, 2021, 2020 and 2019 was approximately $2.0 million, $2.0 million and $0.6 million, respectively.

Litigation

From time to time, we may be involved in disputes, including litigation, relating to claims arising out of operations in the normal course of our business. Any of these claims could subject us to costly legal expenses and, while we generally believe that we have adequate insurance to cover many different types of liabilities, our insurance carriers may deny coverage or our policy limits may be inadequate to fully satisfy any damage awards or settlements. If this were to happen, the payment of any such awards could have a material adverse effect on our results of operations and financial position. Additionally, any such claims, whether or not successful, could damage our reputation and business. We currently are not a party to any legal proceedings, the adverse outcome of which, in management’s opinion, individually or in the aggregate, would have a material adverse effect on our results of operations or financial position.

Related Party Transactions

12 Months Ended

Dec. 31, 2021

Related Party Transactions

11. Related Party Transactions

Our president and chief executive officer is also the sole managing member and a significant stockholder of Araxes Pharma LLC, or Araxes. The following is a summary of related party transactions for the years ended December 31, 2021, 2020 and 2019:

•

Facility Sublease

We subleased office space in San Diego, California from Araxes between June 2017 and June 2020. The monthly rent expense was between $16,000 to $24,000 per month during the sublease term. Rent expense, including operating costs, related to the sublease for the years ended December 31, 2020 and 2019 was approximately $0.2 million and $0.4 million, respectively.

•

Management Fees

We have a management services agreement with Araxes pursuant to which Araxes pays us monthly fees for management services calculated based on costs incurred by us in the provision of services to Araxes, plus a reasonable mark-up. For the years ended December 31, 2021, 2020 and 2019, we recorded approximately $0.1 million, $0.1 million and $0.2 million, respectively, of management fee income included in interest and other income, net on the statements of operations and comprehensive loss. In addition, the agreement allows for Araxes to reimburse us an amount equal to the number of full-time equivalents, or FTE, performing research and development services for Araxes, at an annual FTE rate of approximately $382,000, plus actual expenses as reasonably incurred. For the years ended December 31, 2021 and 2020, we did not record any reimbursements for research and development expenses provided to Araxes. For the year ended December 31, 2019, we recorded reimbursements of approximately $0.1 million, for research and development services provided to Araxes, which was recorded as a reduction to research and development expenses on the statements of operations and comprehensive loss.

•

Services Agreements

We have a services agreement with Wellspring Biosciences, Inc., or Wellspring, a wholly-owned subsidiary of Araxes, pursuant to which we pay Wellspring for research and development services provided to us in an amount equal to the number of FTE’s performing the services, at an annual FTE rate of $400,000, plus actual expenses as reasonably incurred. For the year ended December 31, 2021, we did not recognize any expense under this service agreement. For the years ended December 31, 2020 and 2019, we recognized approximately $0.1 million and $0.2 million, respectively, from research and development services provided to us under this agreement as research and development expense on the statements of operations and comprehensive loss.

We had a services agreement with ALG Partners, Inc., or ALG Partners, a recruiting and temporary staffing agency. Our chief operating officer is an immediate family member of the president of ALG Partners. There were no related party expenses with ALG Partners for the year ended December 31, 2021. For the years ended December 31, 2020 and 2019, expenses recognized as related party transactions with ALG Partners were approximately $0.1 million in both years.

•

Araxes Asset Purchase Agreement

In December 2014, we entered into an asset purchase agreement with Araxes which was amended and restated in February 2015, under which we purchased certain early-stage patent rights related to compounds in the field of oncology for a purchase price of $0.5 million payable under a convertible promissory note. The agreement allows for contingent milestone payments of $9.7 million throughout development and commercialization of the asset, additional payments for each subsequent indication if specified regulatory approvals are achieved and tiered royalties on annual net product sales upon successful commercialization. To date, we have paid Araxes $0.3 million in milestone payments. Additionally, during the year ended December 31, 2020, we announced the termination of our KO-947 ERK inhibitor program and as such do not anticipate having any further obligations due under this agreement. There were no milestone payments to Araxes for the years ended December 31, 2021, 2020 and 2019.

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2021 USD ($) Segment shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Summary Of Significant Accounting Policies [Line Items]
Number of operating segments \| Segment	1
Restricted cash pledged as collateral	$ 210,000	$ 210,000
Impairment losses on long-lived assets	$ 0	$ 0	$ 0
Operating lease, existence of option to extend	true
Operating lease, existence of option to extend description	Lease terms may include options to extend or terminate when we are reasonably certain that the options will be exercised.
Operating lease, existence of option to terminate	true
Operating lease, option to terminate description	Lease terms may include options to extend or terminate when we are reasonably certain that the options will be exercised.
Total potentially dilutive securities \| shares	7,156,000	5,059,000	4,120,000
Computer Software and Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	3 years
Laboratory Equipment
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years
Furniture and Fixtures
Summary Of Significant Accounting Policies [Line Items]
Property and equipment, estimated useful life	5 years
Collateral Pledged
Summary Of Significant Accounting Policies [Line Items]
Restricted cash pledged as collateral	$ 200,000

Long-Term Debt

12 Months Ended

Dec. 31, 2021

Debt Disclosure [Abstract]

Long-Term Debt

6. Long-Term Debt

In November 2018, we entered into a loan and security agreement with Silicon Valley Bank, or the SVB Loan Agreement, providing for up to $20.0 million in a series of term loans. Upon entering into the SVB Loan Agreement, we borrowed $7.5 million, or the Term Loan. The Term Loan had a scheduled maturity date of May 1, 2023. In May 2021, we paid $6.6 million to repay all amounts owed under the Term Loan, which included a final payment of $0.6 million, representing 7.75% of the Term Loan which was being accrued through interest expense using the effective interest method, and a prepayment fee of $30,000. In accordance with ASC 470-50, Debt Modifications and Extinguishments, we accounted for the transaction as an extinguishment of debt. Accordingly, we recorded a loss of approximately $0.2 million in the second quarter of 2021, which is included in interest expense on the statements of operations and comprehensive loss for the year ended December 31, 2021.

- Definition

The entire disclosure for information about short-term and long-term debt arrangements, which includes amounts of borrowings under each line of credit, note payable, commercial paper issue, bonds indenture, debenture issue, own-share lending arrangements and any other contractual agreement to repay funds, and about the underlying arrangements, rationale for a classification as long-term, including repayment terms, interest rates, collateral provided, restrictions on use of assets and activities, whether or not in compliance with debt covenants, and other matters important to users of the financial statements, such as the effects of refinancing and noncompliance with debt covenants.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-URI http://asc.fasb.org/topic&trid=2208564

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (h)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 5: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08(c))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1C
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495334-112611

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-SubTopic 20
-Section 50
-Paragraph 1E
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495348-112611

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

Reference 12: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1I
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495371-112611

Reference 13: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 1B
-Subparagraph (i)
-URI http://asc.fasb.org/extlink&oid=123466505&loc=SL123495323-112611

+ Details

License Agreements

12 Months Ended

Dec. 31, 2021

License Agreements [Abstract]

License Agreements

7. License Agreements

The University of Michigan License Agreement

In December 2014, we entered into a license agreement with the Regents of the University of Michigan, or the University of Michigan, which was amended in March 2015, July 2015, September 2016, February 2017, May 2017 and August 2017, under which we received certain license rights for a non-refundable upfront license, annual maintenance fees and payments upon achievement of certain development and sales-based milestones. The licensed asset consists of several compounds, including our development candidate ziftomenib (KO-539). All future development, regulatory and commercial work on the asset will be completed fully and at our sole expense. The University of Michigan retains the right to use the asset for non-commercial research, internal and/or educational purposes, with the right to grant the same limited rights to other non-profit research institutions.

The agreement will terminate upon the last-to-expire patent rights, or may be terminated by us at any time with 90 days written notice of termination or terminated by the University of Michigan upon a bankruptcy by us, payment failure by us that is not cured within 30 days or a material breach of the agreement by us that is not cured within 60 days.

Janssen License Agreement

In December 2014, we entered into a license agreement with Janssen Pharmaceutica NV, or Janssen, which was amended in June 2016, under which we received certain intellectual property rights related to tipifarnib in all indications other than virology for a non-refundable $1.0 million upfront license fee and payments upon achievement of certain development and sales-based milestones. Tipifarnib is a clinical-stage compound and all ongoing development, regulatory and commercial work will be completed fully and at our sole expense. Under the license agreement, Janssen had a first right to negotiate for an exclusive license back from us to develop and commercialize tipifarnib on terms to be negotiated in good faith. Janssen could exercise this right of first negotiation during a 60-day period following delivery of clinical data as specified in the agreement. In June 2018, Janssen declined to exercise this first right to negotiate.

The agreement will terminate upon the last-to-expire patent rights or last-to-expire royalty term, or may be terminated by us with 180 days written notice of termination. Either party may terminate the agreement in the event of material breach of the agreement that is not cured within 45 days. Janssen may also terminate the agreement due to our lack of diligence that is not cured within a three-month period.

Future Milestone Payments under License Agreements

Collectively, all of our license agreements provide for specified development, regulatory and sales-based milestone payments up to a total of $80.2 million payable upon occurrence of each stated event, of which $0.5 million relates to the initiation of certain development activities, $28.9 million relates to the achievement of specified regulatory approvals for the first indication and up to $50.8 million relates to the achievement of specified levels of product sales. Additional payments will be due for each subsequent indication if specified regulatory approvals are achieved. As of December 31, 2021, we have paid milestone payments totaling $0.1 million under the above-mentioned license agreements. Furthermore, if all the programs are successfully commercialized, we will be required to pay tiered royalties on annual net product sales ranging from the low single digits to the low teens, depending on the volume of sales and the respective agreement.

BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 90,672	$ 325,493
Short-term investments	427,288	307,827
Prepaid expenses and other current assets	4,329	3,972
Total current assets	522,289	637,292
Property and equipment, net	2,673	2,021
Restricted cash	210	210
Operating lease right-of-use assets	5,573	6,334
Other long-term assets	3,306	1,355
Total assets	534,051	647,212
Current liabilities:
Accounts payable and accrued expenses	22,455	23,024
Current portion of long-term debt		3,000
Total current liabilities	22,455	26,024
Long-term debt		4,250
Long-term operating lease liabilities	4,612	5,638
Other long-term liabilities	375	395
Total liabilities	27,442	36,307
Commitments and contingencies (Note 8)
Stockholders' equity:
Preferred stock, $0.0001 par value; 10,000 shares authorized; no shares issued and outstanding
Common stock, $0.0001 par value; 200,000 shares authorized; 66,572 and 66,194 shares issued and outstanding as of December 31, 2021 and 2020, respectively	7	7
Additional paid-in capital	941,359	913,354
Accumulated other comprehensive income (loss)	(1,789)	46
Accumulated deficit	(432,968)	(302,502)
Total stockholders' equity	506,609	610,905
Total liabilities and stockholders' equity	$ 534,051	$ 647,212

Income Taxes - Schedule of Activity Related to Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Gross unrecognized tax benefits at the beginning of the year	$ 2,978	$ 1,741	$ 1,063
Increases related to prior year tax positions	0	0	0
Increases from tax positions taken in the current year	1,424	1,237	678
Gross unrecognized tax benefits at the end of the year	$ 4,402	$ 2,978	$ 1,741

BALANCE SHEETS (Parenthetical) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
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	$ 0.0001	$ 0.0001
Common stock, shares authorized	200,000,000	200,000,000
Common stock, shares issued	66,572,000	66,194,000
Common stock, shares outstanding	66,572,000	66,194,000

STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Operating Expenses:
Research and development	$ 84,721	$ 60,397	$ 47,826
General and administrative	46,537	31,502	19,653
Total operating expenses	131,258	91,899	67,479
Other Income (Expense):
Interest and other income, net	1,206	2,852	4,919
Interest expense	(414)	(578)	(580)
Total other income	792	2,274	4,339
Net Loss	$ (130,466)	$ (89,625)	$ (63,140)
Net loss per share, basic and diluted	$ (1.97)	$ (1.69)	$ (1.51)
Weighted average number of shares used in computing net loss per share, basic and diluted	66,352	53,077	41,946
Comprehensive Loss:
Net loss	$ (130,466)	$ (89,625)	$ (63,140)
Other comprehensive income (loss):
Unrealized gain (loss) on marketable securities and foreign currency	(1,835)	(285)	462
Comprehensive loss	$ (132,301)	$ (89,910)	$ (62,678)

Employee Benefit Plan

12 Months Ended

Dec. 31, 2021

Postemployment Benefits [Abstract]

Employee Benefit Plan

12. Employee Benefit Plan

We have a defined contribution 401(k) plan for all employees. Under the terms of the plan, employees may make voluntary contributions as a percentage or defined amount of compensation. We provided a safe harbor contribution of 4.0% of the employee’s compensation in 2021 and 3.0% in 2020 and prior years, not to exceed eligible limits. For the years ended December 31, 2021, 2020 and 2019, we incurred approximately $1.0 million, $0.6 million and $0.3 million, respectively, in expenses related to the safe harbor contribution.

Share-Based Compensation - Summary of Stock Option Activities (Detail) - Stock Option $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2021 USD ($) $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Stock Options Outstanding, Beginning Balance, Number of Shares \| shares	5,021
Granted, Number of Shares \| shares	2,835
Exercised, Number of Shares \| shares	(343)
Canceled, Number of Shares \| shares	(562)
Stock Options Outstanding, Ending Balance, Number of Shares \| shares	6,951
Vested and expected to vest, Number of Shares \| shares	6,951
Exercisable, Number of Shares \| shares	3,145
Outstanding, Beginning Balance, Weighted-Average Exercise Price per Share \| $ / shares	$ 15.37
Granted, Weighted-Average Exercise Price per Share \| $ / shares	27.70
Exercised, Weighted-Average Exercise Price per Share \| $ / shares	11.11
Canceled, Weighted-Average Exercise Price per Share \| $ / shares	21.94
Outstanding, Ending Balance, Weighted-Average Exercise Price per Share \| $ / shares	20.08
Vested and expected to vest, Weighted-Average Exercise Price per Share \| $ / shares	20.08
Exercisable, Weighted-Average Exercise Price per Share \| $ / shares	$ 16.93
Outstanding, Weighted-Average Remaining Contractual Term (years)	7 years 10 months 24 days
Vested and expected to vest, Weighted-Average Remaining Contractual Term (years)	7 years 10 months 24 days
Exercisable, Weighted-Average Remaining Contractual Term (years)	6 years 10 months 24 days
Outstanding, Aggregate Intrinsic Value \| $	$ 5,565
Vested and expected to vest, Aggregate Intrinsic Value \| $	5,565
Exercisable, Aggregate Intrinsic Value \| $	$ 4,152

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Reclassifications

Certain prior period balances have been reclassified to conform to the current period presentation.

Use of Estimates

Our financial statements are prepared in accordance with accounting principles generally accepted in the United States. The preparation of our financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of expenses during the reporting period.

Reported amounts and note disclosures reflect the overall economic conditions that are most likely to occur and anticipated measures management intends to take. Actual results could differ materially from those estimates. All revisions to accounting estimates are recognized in the period in which the estimates are revised and in any future periods affected.

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. We operate in a single industry segment which is the discovery and development of precision medicines for the treatment of cancer. Our chief operating decision-maker reviews the operating results on an aggregate basis and manages the operations as a single operating segment in the United States.

Cash and Cash Equivalents

Cash and cash equivalents consist of checking, money market and highly liquid investments that are readily convertible to cash and that have an original maturity of three months or less from date of purchase. The carrying amounts approximate fair value due to the short maturities of these instruments.

Restricted Cash

Under the terms of an office lease entered into in March 2020, we are required to maintain a standby letter of credit during the term of the lease. As of December 31, 2021, restricted cash of $0.2 million was pledged as collateral for the letter of credit.

The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported on the balance sheets that sum to the total of the amounts shown on the statements of cash flows, in thousands:


	December 31,
	2021		2020		2019
Cash and cash equivalents	$	90,672	$	325,493	$	26,135
Restricted cash		210		210		—
Total	$	90,882	$	325,703	$	26,135

Short-Term Investments

Short-term investments are marketable securities with maturities greater than three months from date of purchase that are specifically identified to fund current operations. These investments are classified as current assets, even though the stated maturity date may be one year or more beyond the current balance sheet date, which reflects management’s intention to use the proceeds from sales of these securities to fund our operations, as necessary. The cost of short-term investments is adjusted for amortization of premiums or accretion of discounts to maturity, and such amortization or accretion is included in interest income. Dividend and interest income is recognized as interest income on the statements of operations and comprehensive loss when earned. Short-term investments are classified as available-for-sale securities and carried at fair value with unrealized gains and non-credit related losses recorded in other comprehensive income (loss) and included as a separate component of stockholders’ equity. Realized gains and losses from the sale of available-for-sale securities are determined on a specific identification basis and included in interest and other income, net on the statements of operations and comprehensive loss.

Allowance for Credit Losses on Available-for-Sale Debt Securities

Allowance for Credit Losses

For available-for-sale securities in an unrealized loss position, we first assess whether we intend to sell, or if it is more likely than not that we will be required to sell, the security before recovery of its amortized cost basis. If either of the criteria regarding intent or requirement to sell is met, the security’s amortized cost basis is written down to fair value through earnings. For available-for-sale securities that do not meet the aforementioned criteria, we evaluate whether the decline in fair value has resulted from credit losses or other factors. In making this assessment, we consider the severity of the impairment, any changes in interest rates, market conditions, changes to the underlying credit ratings and forecasted recovery, among other factors. The credit-related portion of unrealized losses, and any subsequent improvements, are recorded in interest income through an allowance account. Any impairment that has not been recorded through an allowance for credit losses is included in other comprehensive income (loss) on the statements of operations and comprehensive loss.

We elected the practical expedient to exclude the applicable accrued interest from both the fair value and amortized costs basis of our available-for-sale securities for purposes of identifying and measuring an impairment. Accrued interest receivable on available-for-sale securities is recorded within prepaid expenses and other current assets on our balance sheets. Our accounting policy is to not measure an allowance for credit loss for accrued interest receivable and to write-off any uncollectible accrued interest receivable as a reversal of interest income in a timely manner, which we consider to be in the period in which we determine the accrued interest will not be collected by us.

Concentration of Credit Risk

Financial instruments that potentially subject us to significant concentrations of credit risk consist primarily of cash, cash equivalents and short-term investments. We maintain deposits in federally insured financial institutions in excess of federally insured limits. We have established guidelines to limit our exposure to credit risk by placing investments with high credit quality financial institutions, diversifying our investment portfolio and placing investments with maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.

Fair Value Measurements

Fair value is defined as the 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 guidance establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows:

•

Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities;

•

Level 2 - Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable;

•

Level 3 - Unobservable inputs in which little or no market activity exists, therefore requiring an entity to develop its own assumptions about the assumptions that market participants would use in pricing.

Property and Equipment

Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful lives of the assets. Computer software and equipment are depreciated over their estimated useful lives of three years. Laboratory equipment is depreciated over its estimated useful life of five years. Furniture and fixtures are depreciated over their estimated useful lives of five years. Leasehold improvements are depreciated over the lesser of the term of the related lease or the useful life of the asset.

Impairment of Long-Lived Assets

We review our long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying value of an asset may not be recoverable. If such circumstances are determined to exist, an estimate of undiscounted future cash flows produced by the long-lived asset, including its eventual residual value, is compared to the carrying value to determine whether impairment exists. In the event that such cash flows are not expected to be sufficient to recover the carrying amount of the assets, the assets are written-down to their estimated fair values. For the years ended December 31, 2021, 2020 and 2019, there were no impairments of the value of long-lived assets.

Leases

We determine if an arrangement is a lease or contains lease components at inception. Short-term leases with an initial term of 12 months or less are not recorded on the balance sheet. For operating leases with an initial term greater than 12 months, we recognize operating lease right-of-use, or ROU, assets and operating lease liabilities based on the present value of lease payments over the lease term at commencement date. Operating lease ROU assets are comprised of the lease liability plus any lease payments made and excludes lease incentives. Lease terms may include options to extend or terminate when we are reasonably certain that the options will be exercised. We do not separate lease components from non-lease components. For our operating leases, we generally cannot determine the interest rate implicit in the lease, in which case we use our incremental borrowing rate as the discount rate for the lease. We estimate our incremental borrowing rate for our operating leases based on what we would normally pay to borrow on a collateralized basis over a similar term for an amount equal to the lease payments. Operating lease expense is recognized on a straight-line basis over the lease term.

If a lease is modified, the modified contract is evaluated to determine whether it is or contains a lease. If a lease continues to exist, the lease modification is determined to be a separate contract when the modification grants the lessee an additional ROU that is not included in the original lease and the lease payments increase commensurate with the standalone price for the additional ROU. A lease modification that results in a separate contract will be accounted for in the same manner as a new lease. For a modification that is not a separate contract, we reassess the lease classification using the modified terms and conditions and the facts and circumstances as of the effective date of the modification and recognize the amount of the remeasurement of the lease liability for the modified lease as an adjustment to the corresponding operating lease ROU asset.

Research and Development Expenses

Research and development expenses consist of costs associated with our research and development activities including salaries, benefits, share-based compensation and other personnel costs, clinical trial costs, manufacturing costs for non-commercial products, fees paid to external service providers and consultants, facilities costs and supplies, equipment and materials used in clinical and preclinical studies and research and development. All such costs are charged to research and development expense as incurred when these expenditures have no alternative future uses. We are obligated to make upfront

payments upon execution of certain research and development agreements. Advance payments, including nonrefundable amounts, for goods or services that will be used or rendered for future research and development activities are deferred. Such amounts are recognized as expense as the related goods are delivered or the related services are performed or such time when we do not expect the goods to be delivered or services to be performed. Payments that we make in connection with in-licensed technology for a particular research and development project that have no alternative future uses, in other research and development projects or otherwise, and therefore no separate economic values are expensed as research and development costs at the time such costs are incurred. As of December 31, 2021, we had no in-licensed technologies that have alternative future uses in research and development projects or otherwise.

Clinical Trial Costs and Accruals

A significant portion of our clinical trial costs relate to contracts with contract research organizations, or CROs. The financial terms of our CRO contracts may result in payment flows that do not match the periods over which materials or services are provided to us under such contracts. Our objective is to reflect the appropriate clinical trial expenses in our financial statements by matching those expenses with the period in which services and efforts are expended. As part of the process of preparing our financial statements, we rely on cost information provided by our CROs, concerning monthly expenses as well as reimbursement for pass through costs. We are also required to estimate certain of our expenses resulting from our obligations under our CRO contracts. Accordingly, our clinical trial expense accrual is dependent upon the timely and accurate reporting of CROs and other third-party vendors. If the contracted amounts are modified, for instance, as a result of changes in the clinical trial protocol or scope of work to be performed, we modify our accruals accordingly on a prospective basis. Revisions in the scope of a contract are charged to expense in the period in which the facts that give rise to the revision become reasonably certain. Historically, we have had no material changes in clinical trial expense that had a material impact on our results of operations or financial position.

Patent Costs

We expense all costs as incurred in connection with patent applications, including direct application fees, and the legal and consulting expenses related to making such applications, and such costs are included in general and administrative expenses on the statements of operations and comprehensive loss.

Share-Based Compensation

Our share-based awards are measured at fair value on the date of grant based upon the estimated fair value of common stock. The fair value of awards expected to vest are recognized and amortized on a straight-line basis over the requisite service period of the award less actual forfeitures. The fair value of each stock option is estimated on the date of grant using the Black-Scholes option pricing model, or Black-Scholes model, that requires the use of assumptions including volatility, expected term, risk-free rate and the fair value of the underlying common stock. We estimate the fair value of restricted stock units granted based on the closing market price of our common stock on the date of grant. Actual forfeitures are applied as they occur, and any compensation cost previously recognized for awards for which the requisite service has not been completed is reversed in the period that the award is forfeited.

Income Taxes

Income taxes are accounted for using the asset and liability method. Under the asset and liability method, deferred tax assets and liabilities are recognized for the future tax consequences attributable to differences between the financial carrying amounts of existing assets and liabilities and their respective tax bases and operating loss and tax credit carryforwards. Deferred tax assets and liabilities are measured using enacted tax rates applicable to taxable income in the years in which those temporary differences are expected to be recovered or settled. The effect on deferred tax assets and liabilities of a change in tax rates is recognized in income in the period that includes the enactment date. A valuation allowance against deferred tax assets is recorded if, based upon the weight of all available evidence, it is more likely than not that some or all of the deferred tax assets will not be realized. For uncertain tax positions that meet “a more likely than not” threshold, we recognize the benefit of uncertain tax positions in the financial statements.

Comprehensive Loss

Comprehensive loss is defined as the change in equity during the period from transactions and other events and non-owner sources. For the periods presented, accumulated other comprehensive income (loss) consisted of unrealized gains and losses on marketable securities and foreign currency.

Net Loss per Share

Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding for the period, without consideration for common stock equivalents. Diluted net loss per share is calculated by dividing the net loss by the weighted-average number of common shares and common stock equivalents outstanding for the period determined using the treasury-stock method. As we have reported net loss for the years ended December 31, 2021, 2020 and 2019, dilutive net loss per common share is the same as basic net loss per common share for those periods. Common stock equivalents outstanding are comprised of stock options, restricted stock units, a warrant and employee stock purchase plan rights and are only included in the calculation of diluted earnings per common share when net income is reported and their effect is dilutive. Common stock equivalents outstanding at December 31, 2021, 2020 and 2019 totaling approximately 7,156,000, 5,059,000 and 4,120,000, respectively, were excluded from the computation of dilutive weighted-average shares outstanding because their effect would be anti-dilutive.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board or other standard setting bodies that we adopt as of the specified effective date. We have evaluated recently issued accounting pronouncements and, based on our preliminary assessment, we do not believe any will have a material impact on our financial statements or related footnote disclosures.

Balance Sheet Detail - Summary of Property and Equipment (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 3,517	$ 2,307
Less: accumulated depreciation	(844)	(286)
Property and equipment, net	2,673	2,021
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,532	1,169
Furniture and Fixtures
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,032	862
Laboratory and Computer Equipment
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 953	$ 276

Commitments and Contingencies - Schedule of Maturities of Lease Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Loss Contingency [Abstract]
2022	$ 2,319
2023	2,375
2024	1,863
2025	929
Total lease payments	7,486
Less: imputed interest	(611)
Total operating lease liabilities	$ 6,875	$ 7,700

Share-Based Compensation - Summary of Information Regarding Stock Options (Detail) - Stock Option - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Cash received from options exercised	$ 3,809	$ 9,766	$ 2,562
Intrinsic value of options exercised	$ 3,475	$ 13,348	$ 4,311
Weighted-average grant date fair value per share	$ 17.84	$ 10.15	$ 10.93

Employee Benefit Plan - Additional Information (Detail) - Safe Harbor 401(k) Plan - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Expenses related to contribution plan	$ 1.0	$ 0.6	$ 0.3
Maximum
Defined Contribution Plan Disclosure [Line Items]
Percent of employees compensation	4.00%	3.00%	3.00%

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Schedule of Reconciliation of Cash, Cash Equivalents and Restricted Cash


	December 31,
	2021		2020		2019
Cash and cash equivalents	$	90,672	$	325,493	$	26,135
Restricted cash		210		210		—
Total	$	90,882	$	325,703	$	26,135

Investments (Tables)

12 Months Ended

Dec. 31, 2021

Investments All Other Investments [Abstract]

Investments Measured at Fair Value on Recurring Basis

The following tables summarize, by major security type, our short-term investments that are measured at fair value on a recurring basis, in thousands:


		December 31, 2021
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	1 or less	$	79,895	$	—	$	—		$	79,895

Short-term investments:
Corporate debt securities	3 or less		208,064		—		(892	)		207,172
U.S. Treasury securities	3 or less		135,452		—		(619	)		134,833
Commercial paper	1 or less		53,439		—		—			53,439
Non-U.S. government and supranational debt securities	3 or less		23,122		—		(214	)		22,908
U.S. Agency bonds	2 or less		8,994		—		(58	)		8,936
Total short-term investments			429,071		—		(1,783	)		427,288
Total		$	508,966	$	—	$	(1,783	)	$	507,183


		December 31, 2020
	Maturities (years)	Amortized Cost		Unrealized Gains		Unrealized Losses			Estimated Fair Value
Cash equivalents:
Money market funds	1 or less	$	311,239	$	—	$	—		$	311,239
Commercial paper	1 or less		5,998		—		—			5,998
Total cash equivalents			317,237		—		—			317,237

Short-term investments:
Corporate debt securities	2 or less		113,020		36		(36	)		113,020
U.S. Treasury securities	1 or less		88,409		50		(2	)		88,457
Commercial paper	1 or less		106,350		—		—			106,350
Total short-term investments			307,779		86		(38	)		307,827
Total		$	625,016	$	86	$	(38	)	$	625,064

Share-Based Compensation - Summary of Share-based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 23,579	$ 12,807	$ 9,409
Research and development
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	7,454	3,960	3,427
General and administrative
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense	$ 16,125	$ 8,847	$ 5,982

Stockholders' Equity

12 Months Ended

Dec. 31, 2021

Equity [Abstract]

Stockholders' Equity

9. Stockholders’ Equity

In December 2020, we completed a public offering in which we sold an aggregate of 9,326,500 shares of common stock at a price of $37.00 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $324.1 million.

In May 2020, we completed a public offering in which we sold an aggregate of 10,465,000 shares of common stock at a price of $13.75 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $134.9 million.

In June 2019, we completed a public offering in which we sold an aggregate of 6,785,000 shares of common stock at a price of $17.00 per share. Net proceeds from the public offering, after deducting underwriting discounts, commissions and offering expenses, were approximately $108.1 million.

In March 2019, we entered into an at-the-market issuance sales agreement with SVB Leerink LLC and Stifel, Nicolaus & Company, Incorporated, or ATM facility, under which we may offer and sell, from time to time, at our sole discretion, shares of our common stock having an aggregate offering price of up to $75.0 million. We have not yet sold any shares of our common stock under the ATM facility.

In connection with the loan and security agreement with Oxford Finance LLC and Silicon Valley Bank in 2016, a warrant issued to Oxford Finance LLC to purchase up to 33,988 shares of our common stock at an exercise price of $3.31 per share remains outstanding as of December 31, 2021.

- Definition

The entire disclosure for shareholders' equity comprised of portions attributable to the parent entity and noncontrolling interest, including other comprehensive income. Includes, but is not limited to, balances of common stock, preferred stock, additional paid-in capital, other capital and retained earnings, accumulated balance for each classification of other comprehensive income and amount of comprehensive income.

+ References

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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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+ Details

Share-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	12 Months Ended
	Jan. 01, 2022	Mar. 31, 2015	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based compensation expense			$ 23,579	$ 12,807	$ 9,409
Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			4 years
Closing price of common stock			$ 14.00
Unrecognized estimated stock option compensation expenses			$ 52,300
Weighted average service period			2 years 7 months 6 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting period			4 years
Unrecognized estimated RSUs compensation expenses			$ 4,100
Weighted average service period			3 years 1 month 6 days
Maximum \| Employee Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Term of options to be granted under the Plan			10 years
Amended and Restated 2014 Equity Incentive Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in common shares reserved for future issuance pursuant to future option grants			4.00%
Common shares available for future issuance pursuant to future option grants			905,809
Amended and Restated 2014 Equity Incentive Plan \| Common Stock \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved for issuance			14,882,245
Amended and Restated 2014 Equity Incentive Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future grants	2,662,882
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, Maximum number of share issuable			2,000,000
Share-based compensation expense			$ 300	$ 200	$ 100
Common shares available for future issuance pursuant to future option grants			128,006
Employee stock purchase plan term of offering period		6 months
Percentage of maximum earnings withhold by employee to purchase shares		15.00%
Percentage of common stock purchase		85.00%
Shares issued under ESPP			110,699
2015 Employee Stock Purchase Plan \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage of increase in common shares reserved for future issuance pursuant to future option grants			1.00%
2015 Employee Stock Purchase Plan \| Subsequent Event
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Additional common shares reserved for future issuance pursuant to future grants	665,720

Investments - Investments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Estimated Fair Value	$ 427,288	$ 307,827
Fair Value Measurements on Recurring Basis
Schedule Of Available For Sale Securities [Line Items]
Cash equivalents, Amortized Cost		317,237
Cash equivalents, Estimated Fair Value		317,237
Short-term investments, Amortized Cost	429,071	307,779
Short-term investments, Unrealized Gains		86
Short-term investments, Unrealized Losses	(1,783)	(38)
Short-term investments, Estimated Fair Value	427,288	307,827
Cash equivalents and Short-term investments, Amortized Cost	508,966	625,016
Cash equivalents and Short-term investments, Unrealized Gains		86
Cash equivalents and Short-term investments, Unrealized Losses	(1,783)	(38)
Cash equivalents and Short-term investments, Estimated Fair Value	$ 507,183	$ 625,064
Fair Value Measurements on Recurring Basis \| Money Market Funds
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 or less	1 or less
Cash equivalents, Amortized Cost	$ 79,895	$ 311,239
Cash equivalents, Estimated Fair Value	79,895	311,239
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	208,064	113,020
Short-term investments, Unrealized Gains		36
Short-term investments, Unrealized Losses	(892)	(36)
Short-term investments, Estimated Fair Value	$ 207,172	$ 113,020
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities \| Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 years	2 years
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	$ 135,452	$ 88,409
Short-term investments, Unrealized Gains		50
Short-term investments, Unrealized Losses	(619)	(2)
Short-term investments, Estimated Fair Value	$ 134,833	$ 88,457
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities \| Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 years	1 year
Fair Value Measurements on Recurring Basis \| Commercial Paper
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)		1 or less
Cash equivalents, Amortized Cost		$ 5,998
Cash equivalents, Estimated Fair Value		5,998
Short-term investments, Amortized Cost	$ 53,439	106,350
Short-term investments, Estimated Fair Value	$ 53,439	$ 106,350
Fair Value Measurements on Recurring Basis \| Commercial Paper \| Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	1 year	1 year
Fair Value Measurements on Recurring Basis \| Non U S Government And Supranational Debt Securities
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	$ 23,122
Short-term investments, Unrealized Losses	(214)
Short-term investments, Estimated Fair Value	$ 22,908
Fair Value Measurements on Recurring Basis \| Non U S Government And Supranational Debt Securities \| Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	3 years
Fair Value Measurements on Recurring Basis \| U.S. Agency Bonds
Schedule Of Available For Sale Securities [Line Items]
Short-term investments, Amortized Cost	$ 8,994
Short-term investments, Unrealized Losses	(58)
Short-term investments, Estimated Fair Value	$ 8,936
Fair Value Measurements on Recurring Basis \| U.S. Agency Bonds \| Maximum
Schedule Of Available For Sale Securities [Line Items]
Maturities (years)	2 years

Long-Term Debt - Additional Information (Detail) - USD ($)	1 Months Ended	3 Months Ended	12 Months Ended
	May 31, 2021	Jun. 30, 2021	Dec. 31, 2021	Nov. 01, 2018
Debt Instrument [Line Items]
Prepayment fee related to extinguishment of debt			$ 611,000
Loss from extinguishment of debt			$ 212,000
Silicon Valley Bank \| Term Loan
Debt Instrument [Line Items]
Maximum borrowing capacity under term loans				$ 20,000,000.0
Principal amount outstanding on loan				$ 7,500,000
Description of term loan payment terms			The Term Loan had a scheduled maturity date of May 1, 2023.
Term loan facility maturity date			May 01, 2023
Repayments Of Debt	$ 6,600,000
Final Payment Amount	$ 600,000
Debt Instrument Interest Rate Stated Percentage	7.75%
Prepayment fee related to extinguishment of debt	$ 30,000
Loss from extinguishment of debt		$ 200,000

Balance Sheet Detail

12 Months Ended

Dec. 31, 2021

Balance Sheet Related Disclosures [Abstract]

Balance Sheet Detail

5. Balance Sheet Detail

Property and equipment consisted of the following, in thousands:


	December 31,
	2021			2020
Leasehold improvements	$	1,532		$	1,169
Furniture and fixtures		1,032			862
Laboratory and computer equipment		953			276
Property and equipment, gross		3,517			2,307
Less: accumulated depreciation		(844	)		(286	)
Property and equipment, net	$	2,673		$	2,021

Depreciation expense was $0.6 million and $0.2 million for the years ended December 31, 2021 and 2020, respectively, and de minimis for the year ended December 31, 2019.

Accounts payable and accrued expenses consisted of the following, in thousands:


	December 31,
	2021		2020
Accounts payable	$	3,236	$	2,753
Accrued clinical trial research and development expenses		2,619		4,080
Accrued other research and development expenses		5,341		5,581
Accrued compensation and benefits		7,923		7,016
Operating lease liability, current portion		2,263		2,089
Other accrued expenses		1,073		1,505
Total accounts payable and accrued expenses	$	22,455	$	23,024

Fair Value Measurements - Schedule Of Fair Value Measurements, By Major Security Type (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 427,288	$ 307,827
Fair Value Measurements on Recurring Basis
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		317,237
Short-term investments	427,288	307,827
Cash equivalents and short-term investments	507,183	625,064
Fair Value Measurements on Recurring Basis \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		311,239
Short-term investments	134,833	88,457
Cash equivalents and short-term investments	214,728	399,696
Fair Value Measurements on Recurring Basis \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	292,455	219,370
Cash equivalents and short-term investments	292,455	225,368
Fair Value Measurements on Recurring Basis \| Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	79,895	311,239
Fair Value Measurements on Recurring Basis \| Money Market Funds \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents	79,895	311,239
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	207,172	113,020
Fair Value Measurements on Recurring Basis \| Corporate Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	207,172	113,020
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	134,833	88,457
Fair Value Measurements on Recurring Basis \| U.S. Treasury Securities \| Level 1
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	134,833	88,457
Fair Value Measurements on Recurring Basis \| Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	53,439	106,350
Fair Value Measurements on Recurring Basis \| Commercial Paper \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Cash equivalents		5,998
Short-term investments	53,439	$ 106,350
Fair Value Measurements on Recurring Basis \| Non U S Government And Supranational Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	22,908
Fair Value Measurements on Recurring Basis \| Non U S Government And Supranational Debt Securities \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	22,908
Fair Value Measurements on Recurring Basis \| U S Agency Bonds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	8,936
Fair Value Measurements on Recurring Basis \| U S Agency Bonds \| Level 2
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Short-term investments	$ 8,936

Share-Based Compensation - Summary of Estimate Fair Value of Employee Stock Options and ESPP Using Black-Scholes Model (Detail)	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Stock Option
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected volatility, Minimum	72.00%	74.40%	73.10%
Expected volatility, Maximum	74.60%	76.10%	77.20%
Risk free interest rate, Minimum	0.60%	0.40%	2.10%
Risk free interest rate, Maximum	1.30%	2.00%	2.80%
Stock Option \| Minimum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	5 years 6 months	5 years 6 months	5 years 6 months
Stock Option \| Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 years 29 days	6 years 29 days	6 years 29 days
2015 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (in years)	6 months	6 months	6 months
Expected volatility, Minimum	44.80%	55.30%	43.90%
Expected volatility, Maximum	61.80%	91.90%	54.20%
Risk free interest rate, Minimum	0.00%	0.10%	1.90%
Risk free interest rate, Maximum	0.10%	0.90%	2.50%

Income Taxes - Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020
Deferred tax assets:
Net operating loss carryforwards	$ 111,238	$ 79,230
Research and development tax credit carryforwards	13,794	7,944
Share-based compensation	4,842	2,638
Operating lease liabilities	2,021	2,278
Accruals	2,096	1,915
Other	1,088	641
Total gross deferred tax assets	135,079	94,646
Valuation allowance	(133,206)	(92,523)
Deferred tax assets, net of valuation allowance	1,873	2,123
Deferred tax liabilities:
Operating lease right-of-use assets	(1,638)	(1,868)
Other	(235)	(255)
Total deferred tax liabilities	(1,873)	(2,123)
Net deferred tax assets	$ 0	$ 0

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2021

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

2. Summary of Significant Accounting Policies

Reclassifications

Certain prior period balances have been reclassified to conform to the current period presentation.

Use of Estimates

Segment Reporting

Cash and Cash Equivalents

Restricted Cash


	December 31,
	2021		2020		2019
Cash and cash equivalents	$	90,672	$	325,493	$	26,135
Restricted cash		210		210		—
Total	$	90,882	$	325,703	$	26,135

Short-Term Investments

Allowance for Credit Losses

Concentration of Credit Risk

Fair Value Measurements

•

Level 1 - Quoted prices (unadjusted) in active markets for identical assets or liabilities;

•

Level 2 - Inputs other than quoted prices included within Level 1 that are either directly or indirectly observable;

•

Property and Equipment

Impairment of Long-Lived Assets

Leases

Research and Development Expenses

Clinical Trial Costs and Accruals

Patent Costs

Share-Based Compensation

Income Taxes

Comprehensive Loss

Net Loss per Share

Recent Accounting Pronouncements

Share-Based Compensation

12 Months Ended

Dec. 31, 2021

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Share-Based Compensation

10. Share-Based Compensation

Equity Incentive Plan

In March 2015, our board of directors adopted our Amended and Restated 2014 Equity Incentive Plan, or 2014 Plan, which provides for the grant of incentive stock options, non-statutory stock options, restricted stock awards, restricted stock unit awards, performance-based stock awards and other forms of equity compensation to our employees, consultants and members of our board of directors. The number of shares of our common stock available for future grant under the 2014 Plan will automatically increase on January 1 of each year through January 1, 2025 by 4% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year, subject to the ability of our board of directors to take action to reduce the size of the increase in any given year. On January 1, 2022, an automatic increase pursuant to the 2014 Plan occurred, resulting in 2,662,882 additional shares of common stock available for future grants under the 2014 Plan. We issue shares of common stock upon the exercise of options and vesting of restricted stock unit awards with the source of those shares of common stock being newly issued shares. As of December 31, 2021, 14,882,245 shares of common stock had been reserved for issuance, and 905,809 shares of common stock were available for future grants of equity awards, under the 2014 Plan.

Employee Stock Purchase Plan

In March 2015, our board of directors adopted the 2015 Employee Stock Purchase Plan, or ESPP. The ESPP permits eligible employees to purchase our common stock at a discount through payroll deductions during defined six-month offering periods. Eligible employees may elect to withhold up to 15% of their base earnings to purchase shares of our common stock at a price equal to 85% of the fair market value on the first day of the offering period or the purchase date, whichever is lower. The number of shares of our common stock reserved for issuance under the ESPP will automatically increase on January 1 of each calendar year through January 1, 2025 by the lesser of 1% of the total number of shares of our common stock outstanding on December 31 of the preceding calendar year and 2,000,000 shares of common stock, subject to the ability of our board of directors to take action to reduce the size of the increase in any given year. On January 1, 2022, an automatic increase pursuant to the ESPP occurred, resulting in 665,720 additional shares of common stock available for future grants under the ESPP. As of December 31, 2021, we have issued 110,699 shares of common stock, and 128,006 shares of common stock are reserved for future issuance, under the ESPP. Share-based compensation expense related to the ESPP for the years ended December 31, 2021, 2020 and 2019 was $0.3 million, $0.2 million and $0.1 million, respectively.

Stock Options and Restricted Stock Unit Awards

Stock Options


	Number of Options			Weighted Average Exercise Price per Share		Weighted Average Remaining Contractual Term (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		5,021		$	15.37
Granted		2,835		$	27.70
Exercised		(343	)	$	11.11
Canceled		(562	)	$	21.94
Outstanding at December 31, 2021		6,951		$	20.08		7.9	$	5,565
Vested and expected to vest at December 31, 2021		6,951		$	20.08		7.9	$	5,565
Exercisable at December 31, 2021		3,145		$	16.93		6.9	$	4,152

The aggregate intrinsic value in the above table is calculated as the difference between the closing price of our common stock at December 31, 2021 of $14.00 per share and the exercise price of stock options that had strike prices below the closing price.

The following summarizes certain information regarding stock options, in thousands (except per share data):


	Years Ended December 31,
	2021		2020		2019
Cash received from options exercised	$	3,809	$	9,766	$	2,562
Intrinsic value of options exercised	$	3,475	$	13,348	$	4,311
Weighted-average grant date fair value per share	$	17.84	$	10.15	$	10.93

As of December 31, 2021, unrecognized estimated compensation expense related to stock options was $52.3 million, which is expected to be recognized over the weighted-average remaining requisite service period of approximately 2.6 years.

Restricted Stock Unit Awards

Restricted stock unit awards, or RSUs, are share awards that, upon vesting, will deliver to the holder shares of our common stock. We began issuing RSUs in 2021. The RSUs generally vest annually over four years.

The following is a summary of RSU activity for the year ended December 31, 2021, in thousands (except per share and years data):


	Number of RSUs			Weighted Average Grant Date Fair Value per Share		Weighted Average Remaining Vesting Period (years)		Aggregate Intrinsic Value
Outstanding at December 31, 2020		—		$	—
Granted		187		$	32.80
Released		—		$	—
Canceled		(26	)	$	32.80
Outstanding at December 31, 2021		161		$	32.80		1.6	$	2,261
Expected to vest at December 31, 2021		161		$	32.80		1.6	$	2,261

As of December 31, 2021, unrecognized estimated compensation expense related to RSUs was $4.1 million, which is expected to be recognized over the weighted-average remaining requisite service period of approximately 3.1 years.

Share-Based Compensation Expense

Total share-based compensation expense included on the statements of operations and comprehensive loss was comprised of the following, in thousands:


	Years Ended December 31,
	2021		2020		2019
Research and development	$	7,454	$	3,960	$	3,427
General and administrative		16,125		8,847		5,982
Total share-based compensation expense	$	23,579	$	12,807	$	9,409

We estimated the fair value of employee stock options and ESPP using the Black-Scholes model based on the date of grant with the following assumptions:


	Options						ESPP
	Years Ended December 31,						Years Ended December 31,
	2021		2020		2019		2021		2020		2019
Expected term (in years)	5.50 — 6.08		5.50 — 6.08		5.50 — 6.08			0.50		0.50		0.50
Expected volatility	72.0% — 74.6%		74.4% — 76.1%		73.1% — 77.2%		44.8% — 61.8%		55.3% — 91.9%		43.9% — 54.2%
Risk-free interest rate	0.6% — 1.3%		0.4% — 2.0%		2.1% — 2.8%		0.0%— 0.1%		0.1% — 0.9%		1.9% — 2.5%
Expected dividend yield		—		—		—		—		—		—

Expected term. The expected term of stock options represents the period that the stock options are expected to remain outstanding. Due to limited historical exercise behavior, we determined the expected life assumption using the simplified method. The expected term of the ESPP stock purchase rights is six months, which represents the length of each purchase period.

Expected volatility. The expected volatility was based, in part, on our historical volatility and the historical volatility of comparable publicly-traded companies due to our limited trading history. Expected volatility for the ESPP stock purchase rights is based on our historical volatility.

Risk-free interest rate. The risk-free interest rates are based on the U.S. Treasury zero-coupon bonds with maturities similar to those of the expected term of the award being valued.

Expected dividend yield. The expected dividend yield of zero reflects that we have not paid cash dividends since inception and do not intend to pay cash dividends in the foreseeable future.