Epizyme (EPZM) 10-Q 9 Aug 22 2022 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Aug. 05, 2022
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2022
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Trading Symbol	EPZM
Security Exchange Name	NASDAQ
Title of 12(b) Security	Common stock, $0.0001 par value
Entity Registrant Name	EPIZYME, INC.
Entity Central Index Key	0001571498
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Document Quarterly Report	true
Document Transition Report	false
Entity Common Stock Shares Outstanding		168,364,752
Entity Shell Company	false
Entity File Number	001-35945
Entity Tax Identification Number	26-1349956
Entity Address, Address Line One	400 Technology Square, 4th Floor
Entity Address, City or Town	Cambridge
Entity Address, State or Province	MA
Entity Incorporation, State or Country Code	DE
Entity Address, Postal Zip Code	02139
City Area Code	617
Local Phone Number	229-5872

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Current assets:
Cash and cash equivalents	$ 71,066	$ 98,336
Marketable securities	73,346	78,454
Accounts receivable, net	11,210	6,572
Inventory	5,542	3,216
Prepaid expenses and other current assets	25,676	19,465
Total current assets	186,840	206,043
Property and equipment, net	1,052	1,545
Operating lease assets	18,124	20,054
Intangible assets, net	40,772	42,849
Restricted cash and other assets	17,371	18,509
Total assets	264,159	289,000
Current liabilities:
Accounts payable	5,001	10,265
Accrued expenses	24,671	30,777
Current portion of operating lease obligation	5,282	4,154
Total current liabilities	34,954	45,196
Operating lease obligation, net of current portion	15,546	18,497
Deferred revenue	455	11,950
Related party long-term debt, net of debt discount	216,885	216,461
Related party liability related to sale of future royalties, net of current portion	16,020	15,654
Warrants to purchase common stock	580	1,930
Commitments and contingencies
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 5,000 shares authorized; 0 shares and 338 shares issued and outstanding, respectively (equivalent to 0 shares and to 3,378 shares of common stock upon conversion at a 10:1 ratio)	0	36,127
Common stock, $0.0001 par value; 450,000 shares and 225,000 shares authorized, respectively; 168,365 shares and 106,098 shares issued and outstanding, respectively	17	11
Additional paid-in capital	1,311,038	1,183,006
Accumulated other comprehensive (loss) income	(252)	3
Accumulated deficit	(1,331,084)	(1,239,835)
Total stockholders' equity (deficit)	(20,281)	(20,688)
Total liabilities and stockholders' equity (deficit)	$ 264,159	$ 289,000

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Jun. 30, 2022	Dec. 31, 2021
Statement of Financial Position [Abstract]
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	5,000,000	5,000,000
Preferred stock, shares issued	0	338,000
Preferred stock, shares outstanding	0	338,000
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	450,000,000	225,000,000
Common stock, shares issued	168,365,000	106,098,000
Common stock, shares outstanding	168,365,000	106,098,000
Common stock conversion ratio	10%	10%
Common stock upon conversion	0	3,378,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenue:
Total revenue	$ 27,528	$ 13,010	$ 36,224	$ 20,641
Operating expenses:
Cost of revenue	5,169	2,492	7,808	5,346
Research and development	28,054	34,858	57,834	67,561
Selling, general and administrative	24,111	33,891	51,315	70,303
Total operating expenses	57,334	71,241	116,957	143,210
Operating loss	(29,806)	(58,231)	(80,733)	(122,569)
Other (expense) income, net:
Interest expense , net	(5,392)	(5,581)	(10,871)	(11,057)
Other expense (income), net	(166)	(54)	(214)	(44)
Change in fair value of warrants to purchase common stock	0	0	1,350	0
Related party non-cash interest expense related to sale of future royalties	(380)	(497)	(750)	(967)
Other expense, net	(5,938)	(6,132)	(10,485)	(12,068)
Loss before income taxes	(35,744)	(64,363)	(91,218)	(134,637)
Income tax provision	0	0	(31)	0
Net loss	(35,744)	(64,363)	(91,249)	(134,637)
Other comprehensive income (loss):
Unrealized (loss) gain on available-for-sale securities	(61)	(8)	(255)	(5)
Comprehensive loss	$ (35,805)	$ (64,371)	$ (91,504)	$ (134,642)
Net loss per share attributable to common stockholders:
Basic	$ (0.21)	$ (0.63)	$ (0.59)	$ (1.32)
Diluted	$ (0.21)	$ (0.63)	$ (0.59)	$ (1.32)
Weighted-average common shares outstanding used in net loss per share attributable to common stockholders:
Basic	166,990	102,053	155,658	101,922
Diluted	166,990	102,053	155,658	101,922
Product [Member]
Revenue:
Product revenue, net	$ 11,040	$ 7,984	$ 19,696	$ 14,175
Collaboration and Other Revenue [Member]
Revenue:
Collaboration and other revenue	$ 16,488	$ 5,026	$ 16,528	$ 6,466

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
CASH FLOWS FROM OPERATING ACTIVITIES:
Net loss	$ (91,249)	$ (134,637)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	2,580	2,595
Stock-based compensation	9,740	13,733
Amortization of discount on investments	325	665
Amortization of debt discount	424	382
Change in fair value of warrant liability	(1,350)	0
Non-cash royalty revenue related to sale of future royalties	(66)	0
Non-cash interest expense associated with the sale of future royalties	750	967
Changes in operating assets and liabilities:
Accounts receivable	(4,638)	(4,014)
Inventory, current and noncurrent	(1,841)	(6,629)
Prepaid expenses and other current assets	(5,700)	(2,109)
Accounts payable	(5,265)	(2,886)
Accrued expenses	(6,406)	(59)
Deferred revenue	(11,496)	0
Operating lease assets	1,930	2,092
Operating lease liabilities	(1,823)	(2,313)
Other assets and liabilities	87	(33)
Net cash used in operating activities	(113,998)	(132,246)
CASH FLOWS FROM INVESTING ACTIVITIES:
Purchases of available-for-sale securities	(97,418)	(170,659)
Maturities of available-for-sale securities	101,950	211,539
Purchases of property and equipment	(10)	(221)
Net cash used in investing activities	4,522	40,659
CASH FLOWS FROM FINANCING ACTIVITIES:
Proceeds from issuance of common stock, net of commissions	82,257	1,534
Payment of offering costs	(442)	(105)
Proceeds from stock options exercised	0	916
Proceeds from the issuance of shares under employee stock purchase plan	391	1,191
Net cash provided by financing activities	82,206	3,536
Net decrease in cash, cash equivalents and restricted cash	(27,270)	(88,051)
Cash, cash equivalents and restricted cash, beginning of period	99,845	169,724
Cash, cash equivalents and restricted cash, end of period	72,575	81,673
SUPPLEMENTAL CASH FLOW INFORMATION:
Interest paid	10,785	10,785
Cash paid for income taxes	31	0
Unpaid offering costs	0	154
Property and equipment included in accounts payable or accruals	$ 0	$ 18

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Common Stock [Member]	Preferred Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Loss [Member]
Beginning Balance, Value at Dec. 31, 2020	$ 184,897	$ 10	$ 36,127	$ 1,137,470	$ (988,713)	$ 3
Beginning Balance, Shares at Dec. 31, 2020		101,627,070	337,800
Exercise of stock options and vesting of restricted stock units, Value	199			199
Exercise of stock options and vesting of restricted stock units, Shares		188,000
Stock-based compensation	6,943			6,943
Issuance of shares under employee stock purchase plan, Value	1,191			1,191
Issuance of shares under employee stock purchase plan, Shares		146,049
Issuance of shares of common stock in lieu of board fees	72			72
Issuance of shares of common stock in lieu of board fees, Shares		7,632
Unrealized (loss) gain on available-for-sale securities	3					3
Net loss	(70,274)				(70,274)
Ending Balance, Value at Mar. 31, 2021	123,031	$ 10	$ 36,127	1,145,875	(1,058,987)	6
Ending Balance, Shares at Mar. 31, 2021		101,968,751	337,800
Beginning Balance, Value at Dec. 31, 2020	184,897	$ 10	$ 36,127	1,137,470	(988,713)	3
Beginning Balance, Shares at Dec. 31, 2020		101,627,070	337,800
Unrealized (loss) gain on available-for-sale securities	(5)
Net loss	(134,637)
Ending Balance, Value at Jun. 30, 2021	67,629	$ 10	$ 36,127	1,154,844	(1,123,350)	(2)
Ending Balance, Shares at Jun. 30, 2021		102,249,517	337,800
Beginning Balance, Value at Mar. 31, 2021	123,031	$ 10	$ 36,127	1,145,875	(1,058,987)	6
Beginning Balance, Shares at Mar. 31, 2021		101,968,751	337,800
Issuance of common stock, Value	1,534			1,534
Issuance of common stock, Shares		182,866
Exercise of stock options and vesting of restricted stock units, Value	717			717
Exercise of stock options and vesting of restricted stock units, Shares		93,237
Stock-based compensation	6,679			6,679
Issuance of shares of common stock in lieu of board fees	39			39
Issuance of shares of common stock in lieu of board fees, Shares		4,663
Unrealized (loss) gain on available-for-sale securities	(8)					(8)
Net loss	(64,363)				(64,363)
Ending Balance, Value at Jun. 30, 2021	67,629	$ 10	$ 36,127	1,154,844	(1,123,350)	(2)
Ending Balance, Shares at Jun. 30, 2021		102,249,517	337,800
Beginning Balance, Value at Dec. 31, 2021	(20,688)	$ 11	$ 36,127	1,183,006	(1,239,835)	3
Beginning Balance, Shares at Dec. 31, 2021		106,097,528	337,800
Issuance of common stock, Value	81,828	$ 6		81,822
Issuance of common stock, Shares		58,139,825
Vesting of restricted stock units		276,761
Stock-based compensation	5,238			5,238
Issuance of shares under employee stock purchase plan, Value	391			391
Issuance of shares under employee stock purchase plan, Shares		308,473
Issuance of shares of common stock in lieu of board fees	51			51
Issuance of shares of common stock in lieu of board fees, Shares		45,109
Unrealized (loss) gain on available-for-sale securities	(194)					(194)
Net loss	(55,505)				(55,505)
Ending Balance, Value at Mar. 31, 2022	11,121	$ 17	$ 36,127	1,270,508	(1,295,340)	(191)
Ending Balance, Shares at Mar. 31, 2022		164,867,696	337,800
Beginning Balance, Value at Dec. 31, 2021	(20,688)	$ 11	$ 36,127	1,183,006	(1,239,835)	3
Beginning Balance, Shares at Dec. 31, 2021		106,097,528	337,800
Unrealized (loss) gain on available-for-sale securities	(255)
Net loss	(91,249)
Ending Balance, Value at Jun. 30, 2022	(20,281)	$ 17		1,311,038	(1,331,084)	(252)
Ending Balance, Shares at Jun. 30, 2022		168,364,752
Beginning Balance, Value at Mar. 31, 2022	11,121	$ 17	$ 36,127	1,270,508	(1,295,340)	(191)
Beginning Balance, Shares at Mar. 31, 2022		164,867,696	337,800
Vesting of restricted stock units		83,768
Issuance of Series A Convertible Preferred Stock, net of commissions and beneficial conversion charge, Value			$ (36,127)	36,127
Issuance of Series A Convertible Preferred Stock, net of commissions and beneficial conversion charge, Shares		3,378,000	(337,800)
Stock-based compensation	4,400			4,400
Issuance of shares of common stock in lieu of board fees	51			51
Issuance of shares of common stock in lieu of board fees, Shares		35,288
Offering costs	(48)			(48)
Unrealized (loss) gain on available-for-sale securities	(61)					(61)
Net loss	(35,744)				(35,744)
Ending Balance, Value at Jun. 30, 2022	$ (20,281)	$ 17		$ 1,311,038	$ (1,331,084)	$ (252)
Ending Balance, Shares at Jun. 30, 2022		168,364,752

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Parenthetical) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Jun. 30, 2021
Commissions And Offering Costs	$ 507	$ 49

The Company

The Company	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company	1. The Company Epizyme, Inc. (collectively referred to with its wholly owned, controlled subsidiary, Epizyme Securities Corporation, as “Epizyme” or the “Company”) is a commercial-stage biopharmaceutical company that is committed to rewriting treatment for people with cancer through the discovery, development, and commercialization of novel epigenetic medicines. The Company aspires to change the standard of care for patients and physicians by developing targeted medicines with fundamentally new mechanisms of action directed at specific causes of hematological malignancies and solid tumors. Through June 30, 2022, in addition to revenues from product sales, the Company has raised an aggregate of $ 1,650.2 million to fund its operations. This includes $ 268.8 million of non-equity funding through its collaboration agreements, $ 368.1 million of funding, consisting of $ 150.0 million in equity funding received through agreements with RPI Finance Trust ("RPI"), and $ 218.1 million in debt financing received through a loan agreement with BioPharma Credit Investments V (Master) LP and BPCR Limited Partnership (as transferee of BioPharma Credit Investments V (Master) LP’s interest as a lender) (the "Lenders"), $ 937.3 million from the sale of common stock and series A convertible preferred stock (the “Series A Preferred Stock”) in the Company’s public offerings and at-the-market offerings and $ 76.0 million from the sale of redeemable convertible preferred stock in private financings prior to the Company’s initial public offering in May 2013 . As of June 30, 2022, the Company had $ 144.4 million in cash, cash equivalents and marketable securities. In 2020, the Company’s EZH2 inhibitor, tazemetostat, was approved in the United States as TAZVERIK for the treatment of epithelioid sarcoma ("ES"), and follicular lymphoma ("FL"). Commercial sales of TAZVERIK for the treatment of ES commenced in the first quarter of 2020 and commercial sales of TAZVERIK for the treatment of FL commenced in the end of the second quarter of 2020. The Company commenced active operations in early 2008. Since its inception, the Company has generated an accumulated deficit of $ 1,331.1 million through June 30, 2022 and will require substantial additional capital to fund its research, development, and commercialization efforts. The Company is subject to risks common to companies in the biotechnology industry, including, but not limited to, risks of failure of commercialization, clinical trials and preclinical studies, the need to obtain additional financing to fund the future development and commercialization of tazemetostat and the rest of its pipeline, the need to obtain marketing approval for its product candidates, the need to successfully commercialize and gain market acceptance of TAZVERIK and of any product candidates that may be approved in the future, the impact of the COVID-19 pandemic on the Company’s business, results of operations, and financial condition, dependence on key personnel, protection of proprietary technology, compliance with government regulations, development by competitors of technological innovations and ability to transition from clinical-stage manufacturing to commercial-stage production, marketing, and sale of products. Proposed Acquisition by Ipsen On June 27, 2022, the Company entered into an Agreement and Plan of Merger (the “Merger Agreement”) with Ipsen Pharma SAS, a French société par actions simplifiée (the “Parent”), and Hibernia Merger Sub, Inc., a Delaware corporation and wholly owned subsidiary of Ipsen Biopharmaceuticals, Inc., a Delaware corporation and wholly owned subsidiary of the Parent (“Purchaser”). Pursuant to the Merger Agreement, on July 12, 2022, the Purchaser commenced a tender offer (the “Offer”) to purchase all of the issued and outstanding shares of the Company’s common stock (the “Shares”) at a price of $ 1.45 per Share, payable to the holder of such common stock in cash, without interest, plus one non-transferable contractual contingent value right (“CVR”) per Share, which represents the right to receive one or more payments in cash, of up to $ 1.00 per CVR, contingent upon the achievement of certain specified milestones. As soon as practicable after the consummation of the Offer, and subject to the satisfaction or waiver of certain conditions as set forth in the Merger Agreement, and in accordance with Section 251(h) of the General Corporation Law of the State of Delaware, the Purchaser will be merged with and into the Company, without a meeting of the Company’s stockholders, and the Company will be continuing as the surviving corporation and a wholly owned subsidiary of the Parent (such merger, the “Merger”). As a result of the Merger, the Company will cease to be a publicly traded company. The Merger Agreement contains customary representations, warranties, and covenants. The Company currently expects the Offer and the Merger to be completed in the third quarter of 2022, subject to the satisfaction or waiver of customary closing conditions, including, among others, that the number of Shares tendered in the Offer represent at least one Share more than 50 % of the total number of Shares outstanding immediately prior to the expiration of the Offer. The Merger Agreement provides the Parent and the Company with certain termination rights and, under certain circumstances, may require the Company to pay the Parent a termination fee of $ 9.9 million. For additional information related to the Merger Agreement, refer to the Company’s Solicitation/Recommendation Statement on Schedule 14D-9 filed with the U.S. Securities and Exchange Commission (“SEC”) on July 12, 2022, together with the exhibits and annexes thereto and as amended or supplemented from time to time. Please also see “Item 1A. Risk Factors—Risks Related to Our Pending Transaction with Ipsen Pharma SAS” of this Quarterly Report on Form 10-Q. Operating Cost Reduction In August 2021, the Company implemented a cross-functional reduction of approximately 11 % of its then current workforce under a cost reduction plan. Affected employees were offered separation benefits, including severance payments along with temporary healthcare coverage assistance. The severance and termination-related costs totaled approximately $ 2.0 million, $ 1.6 million of which were recorded as selling general and administrative expenses and $ 0.4 million of which was recorded as research and development expenses in the third quarter of 2021. The Company expects that payments of these costs will be made through August 2022. In March 2022, the Company implemented further reductions of its expenses, including a pipeline reprioritization. Given the breadth of the Company’s then-current tazemetostat clinical development program, the Company decided to discontinue enrollment in its Phase 2 study of tazemetostat in combination with rituximab with FL in the third-line or later treatment settings (SYMPHONY-2, EZH-1401), as well as in its Phase 1/1b basket study evaluating tazemetostat combinations in patients with solid tumors (EZH-1301). The decision to discontinue these studies was based on evolving market dynamics and a continued focus on optimizing the Company’s investments and eliminating potentially overlapping studies. The Company continues to study tazemetostat in combination with other therapies for both hematologic and solid tumor malignancies, both in ongoing Company-sponsored studies as well as investigator-initiated studies. In addition, as part of the cost reduction plan, the Company implemented a cross-functional workforce reduction of approximately 12 % of the Company’s then-current employees. The severance and termination related costs totaled approximately $ 2.5 million, $ 1.7 million of which were recorded as selling general and administrative expenses and $ 0.8 million of which were recorded as research and development expenses in the first quarter of 2022. The Company expects that payments of these costs will be made through December 2022.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2022
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2021, or the Annual Report. The unaudited condensed consolidated financial statements include the accounts of Epizyme, Inc. and its wholly owned, controlled subsidiary, Epizyme Securities Corporation. All intercompany transactions and balances of subsidiaries have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the condensed consolidated financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2022 and 2021 are referred to as the second quarter of 2022 and 2021 , respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period. Use of Estimates The preparation of these condensed consolidated financial statements in accordance with accounting principles generally accepted in the United States requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities, as of the date of the condensed consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results and outcomes may differ materially from management’s estimates, judgments and assumptions. Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three and six months ended June 30, 2022 are consistent with those discussed in Note 2 to the consolidated financial statements in the Annual Report and are updated below as necessary. Going Concern At each reporting period, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company is required to make certain additional disclosures if it concludes substantial doubt exists about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued and such doubt is not alleviated by the Company’s plans or when the Company's plans alleviate substantial doubt about the Company’s ability to continue as a going concern. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs, and comparing those needs to its available cash, cash equivalents and marketable securities. The Company has recurring losses and expects to have recurring losses for the foreseeable future with the continued commercialization of TAZVERIK in ES and FL, the development of tazemetostat in other indications, and the development of the Company’s other product candidates. In addition, the Company has experienced and continues to experience challenges in the commercialization of TAZVERIK resulting from the ongoing COVID-19 pandemic, which the Company believes has had an adverse impact on TAZVERIK revenues. In response to the challenges that the Company has continued to face since the Company commenced its launch of TAZVERIK in FL in June 2020, the Company implemented an operational cost reduction plan in August 2021, implemented further expense reductions in March 2022, and continues to evaluate its costs on an ongoing basis with the intention to streamline such costs. In addition, in connection with its ongoing review of the Company’s strategic plans and financing needs, the Company’s board of directors established a special committee in January 2022 to work with the Company’s management in connection with the exploration and consideration of a possible strategic transaction, a possible equity financing and a possible restructuring or refinancing of the Company’s outstanding indebtedness under the Amended and Restated Loan Agreement. The analysis of the Company’s ability to continue as a going concern for the second quarter of 2022 included consideration of the Company’s current cash needs, including its research and development plans, commercialization activities associated with the continued commercialization of TAZVERIK in the ES and FL indications, its existing debt service obligations, anticipated cost savings resulting from its operational cost reduction plans, including ongoing efforts to eliminate costs not related to the Company’s strategic focus. The analysis included forecasted product revenues from sales of TAZVERIK. Such estimates of future sales contain significant judgment as TAZVERIK was first launched in the first half of 2020 and there is little history with which to base such estimates. In addition, the Company’s ongoing efforts to eliminate costs not related to the Company’s strategic focus contains uncertainties as to whether the Company can attain such benefits. Based on the analysis, the Company concluded that its available cash, cash equivalents and marketable securities as of June 30, 2022 will not be sufficient to fund current planned operations and capital expenditure requirements and pay its debt service obligations as they become due through at least 12 months from the date these financial statements are issued. These conditions raise substantial doubt about the Company’s ability to continue as a going concern for a period of at least one year from the date these financial statements are issued. The Company’s ability to continue to fund its operations is dependent on management’s plans, which include the proposed acquisition by Ipsen described above. The Company’s current operating plan is based on assumptions that may prove to be wrong including that the proposed merger with Ipsen will close, and the Company could use its capital resources sooner than it expects, in which case the Company would evaluate further reductions in its expenses or obtaining additional financing sooner than it otherwise would through equity or debt financing, which additional financing may not be available or may only be available on terms that are not acceptable to the Company. Due to the inherent uncertainties with respect to these actions, management concluded they were not probable of occurrence and therefore do not mitigate the conditions that raise substantial doubt about the Company’s ability to continue as a going concern. The accompanying unaudited condensed consolidated financial statements do not include any adjustments that might be necessary if the Company is not able to continue as a going concern. Recently Adopted Accounting Pronouncements In August 2020, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”) to simplify accounting for certain financial instruments. ASU 2020-06 eliminates the current models that require separation of beneficial conversion and cash conversion features from convertible instruments and simplifies the derivative scope exception guidance pertaining to equity classification of contracts in an entity’s own equity. The new standard also introduces additional disclosures for convertible debt and freestanding instruments that are indexed to and settled in an entity’s own equity. ASU 2020-06 amends the diluted earnings per share guidance, including the requirement to use the if-converted method for all convertible instruments. The Company adopted ASU 2020-06 effective as of January 1, 2022. The adoption of ASU 2020-06 did not have an impact on the Company’s financial statements. Revenue Recognition The Company recognizes revenue when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. For a further discussion of accounting for net product revenue see Note 3, Product Revenue, Net . Other Revenue Other revenue consists of revenue from the sales of tazemetostat active pharmaceutical ingredient ("API"), drug product to the Company’s licensees or collaborators and non-cash royalty revenue related to sale of future royalties. The Company recognizes revenue on tazemetostat API and drug product when control has transferred under the terms of each agreement. Cost of Revenues Cost of revenues primarily consists of costs related to the sales of TAZVERIK and sales of tazemetostat API and drug product to the Company’s licensees or collaborators. These costs include materials, labor, manufacturing overhead, amortization of milestone payments, and royalties payable on net sales of TAZVERIK. Cost of revenues for each of the three and six months ended June 30, 2022 included approximately $ 2.3 million related to sales of tazemetostat drug product. Cost of revenues for the six months ended June 30, 2021 included approximately $ 0.8 million related to sales of tazemetostat drug product. There were no sales of tazemetostat drug product during the three months ended June 30, 2021. Accounts Receivable The Company extends credit to customers based on its evaluation of the customer’s financial condition. The Company records receivables for all billings when amounts are due under standard terms. Accounts receivable are stated at amounts due net of applicable prompt pay discounts and other contractual adjustments as well as an allowance for doubtful accounts. The Company assesses the need for an allowance for doubtful accounts by considering a number of factors, including the length of time trade accounts receivable are past due, the customer’s ability to pay its obligation and the condition of the general economy and the industry as a whole. The Company will write off accounts receivable when the Company determines that they are uncollectible. In general, the Company has experienced no significant collection issues with its customers. Inventory The Company outsources the manufacturing of TAZVERIK and uses contract manufacturers to produce the raw and intermediate materials used in the production of TAZVERIK as well as the finished product. The Company currently has one supplier qualified for each step in the manufacturing process and is in the process of qualifying additional suppliers. Inventory is composed of raw materials, intermediate materials, which are classified as work-in-process, and finished goods, which are goods that are available for sale. The Company states inventory at the lower of cost or net realizable value with the cost based on the first-in, first-out method. Inventory is classified as long-term when it is expected to be utilized beyond the Company’s normal operating cycle and is included in restricted cash and other assets on the Company's condensed consolidated balance sheets. If the Company identifies excess, obsolete or unsalable items, it writes down its inventory to its net realizable value in the period in which the impairment is identified. These adjustments are recorded based upon various factors related to the product, including the level of product manufactured by the Company, the level of product in the distribution channel, current and projected demand, the expected shelf-life of the product and firm inventory purchase commitments. Shipping and handling costs incurred for inventory purchases are included in inventory costs and costs incurred for product shipments are recorded as incurred in cost of revenue. Intangible Assets, Net Intangible assets consist of capitalized milestone payments made to third parties under an in-license of patent rights upon receiving regulatory approval of TAZVERIK. The finite-lived intangible assets are being amortized on a straight-line basis over the expected time period the Company will benefit from the in-licensed rights, which is generally the patent life. Intangible assets are recorded at cost at the time of their acquisition and are stated in the Company’s condensed consolidated balance sheets net of accumulated amortization and impairments, if applicable. The amortization expense is recognized as cost of revenue in the Company’s condensed consolidated statement of operations and comprehensive loss. During 2020 the Company paid a total of $ 50.0 million in milestone payments under its agreement with Eisai, Co., Ltd. (“Eisai”) following regulatory approval of tazemetostat for ES and FL. These regulatory milestones have been capitalized as intangible assets. The following table presents intangible assets as of June 30, 2022 (in thousands): June 30, 2022 Estimated useful In-licensed rights $ 50,000 12.2 Less: accumulated amortization ( 9,228 ) Total intangible asset, net $ 40,772 The Company recorded approximately $ 1.0 million and $ 2.1 million in amortization expense related to intangible assets, using the straight-line methodology, during each of the three and six months ended June 30, 2022 and 2021, respectively. Estimated future amortization expense for intangible assets for the remainder of the year ended December 31, 2022 is $ 2.1 million and approximately $ 4.2 million per year thereafter. The Company assesses its intangible assets for impairment if indicators are present or changes in circumstance suggest that impairment may exist. Events that could result in an impairment, or trigger an interim impairment assessment, include the receipt of additional clinical or nonclinical data regarding one of the Company’s drug candidates or a potentially competitive drug candidate, changes in the clinical development program for a drug candidate, or new information regarding potential sales for the drug. If impairment indicators are present or changes in circumstance suggest that impairment may exist, the Company performs a recoverability test by comparing the sum of the estimated undiscounted cash flows of each intangible asset to its carrying value on the Company's condensed consolidated balance sheets. If the undiscounted cash flows used in the recoverability test are less than the carrying value, the Company would determine the fair value of the intangible asset and recognize an impairment loss if the carrying value of the intangible asset exceeds its fair value. During the three months ended June 30, 2021, the Company concluded the lower than anticipated current and projected future revenue, due to the impact of the COVID-19 pandemic as well as other factors, was an indicator that impairment may exist related to its finite-lived intangible assets. As a result, the Company performed a recoverability test and determined that the finite-lived intangible assets were recoverable. The Company’s quantitative assessment considered significant assumptions related to estimates of future TAZVERIK sales, offset by direct costs to derive the sales. The estimates of future TAZVERIK sales and associated costs included estimates of significant growth, however, these estimates were uncertain as the product was first launched in the first half of 2020 and due to the uncertainties associated with the ongoing COVID-19 pandemic. Given the limited history of sales and the inherent difficulty in making a long-range forecast, such estimates contained significant uncertainty. If the assumptions regarding forecasted revenue or the costs to derive such revenues made at that time prove to be inaccurate, the Company may be required to perform future impairment analyses and record an impairment charge for its intangible assets in future periods.

Product Revenue Net

Product Revenue Net	6 Months Ended
	Jun. 30, 2022
TAZVERIK [Member]
Concentration Risk [Line Items]
Product Revenue Net	3. Product Revenue, Net The Company sells TAZVERIK in the United States principally to a limited number of specialty pharmacies, which dispense the product directly to patients and specialty distributors, which in turn sell the product to hospital pharmacies and community practice pharmacies (collectively, healthcare providers) for the treatment of patients. The specialty pharmacies and specialty distributors are referred to as the Company’s customers. Product revenue is recognized by the Company in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services when the customer obtains control of the product, which occurs at a point in time, typically when the product is received by the Company’s customers. The Company provides a right of return to its customers for unopened product for a limited time before and after its expiration date, which right of return lapses upon shipment to a patient. Healthcare providers to whom specialty distributors sell TAZVERIK hold limited inventory that is designated for patients, and the Company monitors inventory levels in the distribution channel to limit the risk of return. Reserves for Variable Consideration Revenues from product sales are recorded as product revenue at the net sales price (transaction price), which includes estimates of variable consideration for which reserves are established and which result from discounts, returns, chargebacks, rebates, co-pay assistance and other allowances that are offered within contracts between the Company and its customers, healthcare providers, payors and other indirect customers relating to the Company’s product sales. These reserves are based on the amounts earned or to be claimed on the related sales and are classified as reductions of accounts receivable (if the amount is payable to the customer) or a current liability (if the amount is payable to a party other than a customer). Where appropriate, these estimates take into consideration a range of possible outcomes that are probability-weighted for relevant factors such as the Company’s historical experience, current contractual and statutory requirements, specific known market events and trends, industry data and forecasted customer buying and payment patterns. Overall, these reserves reflect the Company’s best estimates of the amount of consideration to which the Company is entitled based on the terms of the contract(s). The amount of variable consideration that is included in the transaction price may be constrained, and is included in the net sales price only to the extent that it is probable that a significant reversal in the amount of the cumulative revenue recognized will not occur in a future period. Actual amounts of consideration ultimately received may differ from the Company’s estimates. If actual results in the future vary from the Company’s estimates, the Company will adjust these estimates, which would affect net product revenue and earnings in the period such variances become known. Trade Discounts and Allowances : The Company generally provides customers with discounts that include incentive fees that are explicitly stated in customer contracts and are recorded as a reduction of revenue in the period the related product revenue is recognized. In addition, the Company receives sales order management, data and distribution services from certain customers. To the extent the services received are distinct from the Company’s sale of products to the customer, these payments are classified in selling, general and administrative expenses in the Company's condensed consolidated statements of operations and comprehensive loss. Product Returns : Consistent with industry practice, the Company generally offers customers a limited right of return based on the product’s expiration date for product that has been purchased from the Company, which lapses upon shipment to a patient. The Company estimates the amount of product sales that may be returned by customers and records this estimate as a reduction of revenue in the period in which the related product revenue is recognized. The Company currently estimates product return liabilities using available industry data and the Company’s own historical sales information, including its visibility into the product remaining in the distribution channel. Provider Chargebacks and Discounts : Chargebacks for fees and discounts to healthcare providers represent the estimated obligations resulting from contractual commitments to sell products to qualified healthcare providers at prices lower than the list prices charged to customers who directly purchase the product from the Company. Customers charge the Company for the difference between what they pay for the product and the ultimate selling price to the qualified healthcare providers. These reserves are established in the same period that the related revenue is recognized, resulting in a reduction of product revenue and accounts receivable. Chargeback amounts are generally determined at the time of resale to the qualified healthcare provider by customers, and the Company generally issues credits for such amounts within a few weeks of the customer’s notification to the Company of the resale. Reserves for chargebacks consist of credits that the Company expects to issue for units that remain in the distribution channel at each reporting period end that the Company expects will be sold to qualified healthcare providers, and chargebacks that customers have claimed but for which the Company has not yet issued a credit. Government Rebates: The Company is subject to discount obligations under state Medicaid programs and Medicare. The Company estimates its Medicaid and Medicare rebates based upon a range of possible outcomes that are probability-weighted for the estimated payor mix. These reserves are recorded in the same period in which the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability that is included in accrued expenses on the Company’s condensed consolidated balance sheets. For Medicare, the Company also estimates the number of patients in the prescription drug coverage gap for whom the Company will owe an additional liability under the Medicare Part D program. The Company’s liability for these rebates consists of invoices received for claims from prior quarters that have not been paid or for which an invoice has not yet been received, estimates of claims for the current quarter, and estimated future claims that will be made for product that has been recognized as revenue, but remains in the distribution channel inventories at period end. Payor Rebates: The Company may contract with various private payor organizations, primarily insurance companies and pharmacy benefit managers, for the payment of rebates with respect to utilization of the Company’s products. The Company estimates these rebates and records such estimates in the same period the related revenue is recognized, resulting in a reduction of product revenue and the establishment of a current liability. Other Incentives/Patient Assistance Programs: The Company also offers voluntary patient assistance programs such as co-pay assistance. Co-pay assistance programs are intended to provide financial assistance to qualified commercially insured patients with prescription drug co-payments required by payors. The calculation of the accrual for co-pay assistance is based on an estimate of claims and the cost per claim that the Company expects to receive associated with product that has been recognized as revenue, but remains in the distribution channel inventories at period end. The following table summarizes activity in each of the above product revenue allowances and reserve categories for the six months ended June 30, 2022: Chargebacks, Government Fees Rebates Returns Total (In thousands) Balance, January 1, 2022 $ 244 $ 586 $ 109 $ 939 Provision 1,139 2,539 22 3,700 Payments or credits ( 1,106 ) ( 2,423 ) — ( 3,529 ) Balance, June 30, 2022 $ 277 $ 702 $ 131 $ 1,110 Concentration of Credit Risk Financial instruments which potentially subject the Company to concentrations of credit risk consist of accounts receivable from customers and cash held at financial institutions. The Company believes that such customers and financial institutions are of high credit quality. For the three and six months ended June 30, 2022 and 2021, net product revenue was primarily generated from four individual customers. Revenue earned from each customer as a percentage of net product revenue is as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 Customer 1 37 % 31 % 40 % 36 % Customer 2 9 % 8 % 10 % 11 % Customer 3 14 % 46 % 17 % 37 % Customer 4 24 % 14 % 21 % 16 % Customer 5 16 % 0 % 11 % 0 % As of June 30, 2022 and December 31, 2021, the five individual customers represented as a percentage of accounts receivable as follows: June 30, December 31, Customer 1 21 % 15 % Customer 2 12 % 10 % Customer 3 16 % 22 % Customer 4 25 % 29 % Customer 5 26 % 24 % No other customer represented more than 10 percent of net product revenue or accounts receivable.

Cash

Cash	6 Months Ended
	Jun. 30, 2022
Cash and Cash Equivalents [Abstract]
Cash	4. Cash A reconciliation of cash, cash equivalents, and restricted cash reported within the Company's condensed consolidated balance sheets that sum to the total of the same such amounts shown in the Company's condensed consolidated statements of cash flows, is as follows: As of June 30, 2022 2021 (In thousands) Cash and cash equivalents $ 71,066 $ 80,164 Restricted cash, as part of other assets 1,509 1,509 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 72,575 $ 81,673 The $ 1.5 million in restricted cash as of both June 30, 2022 and 2021 is comprised of $ 0.5 million in a letter of credit as a security deposit for the Company’s office and laboratory lease at Technology Square in Cambridge, Massachusetts and $ 1.0 million in a letter of credit as a security deposit for the Company’s office lease at Hampshire Street in Cambridge, Massachusetts. The Company has recorded cash held to secure these letters of credit as restricted cash in restricted cash and other assets on its condensed consolidated balance sheets. The restricted cash is classified as non-current based on the related lease terms.

Marketable Securities

Marketable Securities	6 Months Ended
	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	5. Marketable Securities The following table summarizes the available-for-sale securities held at June 30, 2022 (in thousands): Description Amortized Unrealized Unrealized Fair Value Commercial paper $ 15,942 $ — $ ( 16 ) $ 15,926 U.S. government agency securities and U.S. Treasuries 57,653 — ( 233 ) 57,420 Total $ 73,595 $ — $ ( 249 ) $ 73,346 The following table summarizes the available-for-sale securities held at December 31, 2021 (in thousands): Description Amortized Unrealized Unrealized Fair Value Commercial paper $ 68,427 $ 7 $ ( 3 ) $ 68,431 U.S. government agency securities and U.S. Treasuries 10,025 — ( 1 ) 10,024 Total $ 78,452 $ 7 $ ( 4 ) $ 78,455 Certain short-term debt securities with original maturities of less than 90 days are included in cash and cash equivalents within the Company's condensed consolidated balance sheets and are not included in the tables above. The amortized cost of available-for-sale securities is adjusted for amortization of premiums and accretion of discounts to maturity. At June 30, 2022 , the balance in the Company’s accumulated other comprehensive loss was composed solely of activity related to the Company’s available-for-sale marketable securities. There were no realized gains or losses recognized on the sale or maturity of available-for-sale securities during the six months ended June 30, 2022, and as a result, the Company did not reclassify any amounts out of accumulated other comprehensive loss for the same period. The aggregate fair value of available-for-sale securities held by the Company in an unrealized loss position for less than twelve months as of June 30, 2022 was $ 73.3 million, which consisted of 4 commercial paper securities and 14 United States Treasury securities. The aggregate unrealized loss for those securities in an unrealized loss position for less than twelve months as of June 30, 2022 was less than $ 0.3 million. The Company does not intend to sell and it is unlikely that the Company will be required to sell the above investments before recovery of their amortized cost bases, which may be maturity. The Company has determined that there has been no material change in the credit risk of any of its investments. As a result, the Company determined it did not hold any investments that were impaired as of June 30, 2022 . The Company reviews its portfolio of available-for-sale debt securities, using both quantitative and qualitative factors, to determine if declines in fair value below cost have resulted from a credit-related loss or other factors. If the decline in fair value is due to credit-related factors, a loss is recognized in net income, whereas if the decline in fair value is not due to credit-related factors, the loss is recorded in other comprehensive income (loss). The weighted-average maturity of the Company’s portfolio was approximately three months at June 30, 2022 .

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2022
Fair Value Disclosures [Abstract]
Fair Value Measurements	6. Fair Value Measurements The Company’s financial instruments as of June 30, 2022 and December 31, 2021 consisted primarily of cash and cash equivalents, marketable securities and accounts receivable and accounts payable. As of June 30, 2022 and December 31, 2021, the Company’s financial assets recognized at fair value consisted of the following: Fair Value as of June 30, 2022 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 61,518 $ 40,355 $ 21,163 $ — Marketable securities: Commercial paper 15,926 — 15,926 — U.S. government agency securities and treasuries 57,420 — 57,420 — Total $ 134,864 $ 40,355 $ 94,509 $ — Fair Value as of December 31, 2021 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 88,637 $ 67,209 $ 21,428 $ — Marketable securities: Commercial paper 68,431 — 68,431 — U.S. government agency securities and treasuries 10,024 — 10,024 — Total $ 167,092 $ 67,209 $ 99,883 $ — Cash equivalents and marketable securities have been initially valued at the transaction price and subsequently valued, at the end of each reporting period, utilizing third-party pricing services or other market observable data. The Company measures its cash equivalents at fair value on a recurring basis, which approximates the net asset value per share. The Company classifies some of its cash equivalents within Level 1 of the fair value hierarchy because they are valued using observable inputs that reflect quoted prices for identical assets in active markets. The Company measures its marketable securities at fair value on a recurring basis and classifies those instruments and some cash equivalents within Level 2 of the fair value hierarchy. The pricing services used by management utilize industry standard valuation models, including both income- and market- based approaches and observable market inputs to determine the fair value of marketable securities and those cash equivalents classified within Level 2 of the fair value hierarchy.

Inventory

Inventory	6 Months Ended
	Jun. 30, 2022
Inventory Disclosure [Abstract]
Inventory	7. Inventory All of the Company’s inventory relates to the manufacturing of TAZVERIK. The following table sets forth the Company’s inventory as of June 30, 2022 and December 31, 2021: June 30, December 31, (In thousands) Raw materials $ 1,676 $ 3,227 Work in process 17,930 13,748 Finished goods 917 1,710 Total $ 20,523 $ 18,685 Balance sheet classification Inventory $ 5,542 $ 3,216 Restricted cash and other assets 14,981 15,469 Total $ 20,523 $ 18,685 The Company’s active pharmaceutical ingredient has a long shelf life and the Company’s finished drug product has a three-year expiry, however the realizability of the inventory is subject to forecasted future sales of TAZVERIK. The Company’s forecasted sales currently support the realizability of the Company’s inventory but are uncertain and could change in the future, which would require the Company to write down the value of such inventory. As of June 30, 2022 the Company has not capitalized inventory costs related to its other drug development programs.

Supplemental Balance Sheet Info

Supplemental Balance Sheet Information	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Supplemental Balance Sheet Information	8. Supplemental Balance Sheet Information Accrued expenses consisted of the following: June 30, December 31, (In thousands) Employee compensation and benefits $ 7,614 $ 11,737 Research and development expenses 10,488 13,744 Current portion of liability related to the sale of future royalties 592 273 Professional services and other 5,977 5,023 Accrued expenses $ 24,671 $ 30,777

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2022
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The Company recorded less than $ 0.1 million of federal or state income tax provision for the three and six months ended June 30, 2022 due to the expected and known loss before income taxes to be incurred, or incurred, as applicable, for the year ended December 31, 2022, as well as the Company’s continued maintenance of a full valuation allowance against its net deferred tax assets. The Company did no t record a federal or state income tax provision or benefit for the three and six months ended June 30, 2021 due to the expected and known loss before income taxes to be incurred, or incurred, as applicable, for the year ended December 31, 2021, as well as the Company’s continued maintenance of a full valuation allowance against its net deferred tax assets.

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2022
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and Contingencies Legal Proceedings The Company, from time to time, may be party to litigation arising in the ordinary course of its business. The Company was not subject to any material legal proceedings during the three and six months ended June 30, 2022. Subsequent to June 30, 2022, a number of complaints have been filed in federal court by purported stockholders of the Company regarding the Agreement and Plan of Merger (the “Merger Agreement”) by and among the Company, Ipsen Pharma SAS, a French société par actions simplifiée (the “Parent”), and Hibernia Merger Sub, Inc., a Delaware corporation (the “Purchaser”) and a wholly owned subsidiary of Ipsen Biopharmaceuticals, Inc., a Delaware corporation, dated as of June 27, 2022. The complaints generally contend that the Solicitation/Recommendation Statement on Schedule 14D-9, filed on July 12, 2022, has omitted or misrepresented material information regarding the merger. The complaints seek, among other relief, (i) injunctive relief preventing the consummation of the transaction contemplated by the Merger Agreement; (ii) rescission or rescissory damages in the event the Merger Agreement is implemented; (iii) other damages purportedly incurred on account of defendants’ alleged misstatements or omissions; (iv) dissemination of an Amendment to the Schedule 14D-9 that discloses certain information requested by the plaintiffs; (v) declaratory relief stating defendants violated the Exchange Act of 1934, as amended; and (vi) an award of plaintiffs’ expenses and attorneys’ fees. The Company believes that the claims asserted in the complaints are without merit. Additional lawsuits arising out of or relating to the Merger Agreement may be filed in the future. For a description of the Company's material legal proceedings since June 30, 2022, see "Part II. Other Information - Item 1. Legal Proceedings" of this Quarterly Report on Form 10-Q. Merger Agreement In connection with a termination of the Merger Agreement under certain circumstances, including termination by the Company in order to accept and enter into a definitive agreement with respect to a Superior Proposal (as defined in the Merger Agreement), the Company will be required to pay the Parent a termination fee of $ 9.9 million. Other There have been no other significant changes to the Company’s commitments and contingencies, other than the minimum lease payments as disclosed in Note 11, Leases , in the three and six months ended June 30, 2022, as compared to those disclosed in Note 9, Commitments and Contingencies , included in the Annual Report.

Leases

Leases	6 Months Ended
	Jun. 30, 2022
Leases [Abstract]
Leases	11. Leases The Company enters into lease arrangements for its facilities as well as certain equipment. A summary of the arrangements is as follows: Operating Leases The Company leases office and laboratory space at Technology Square in Cambridge, Massachusetts under a Lease Agreement, dated as of June 15, 2012, as amended (the "Technology Square Lease") with ARE-TECH Square, LLC, a Delaware limited liability company. In May 2017, the Company exercised its option to extend the term of the Technology Square Lease to November 30, 2022. Under the Technology Square Lease as amended, the Company agreed to pay a monthly base rent of approximately $ 0.2 million for the period commencing December 1, 2017 through May 31, 2018, with an increase on June 1, 2018 of approximately $ 33,000 and annual increases of approximately $ 9,000 on December 1 of each subsequent year until the last increase, which occurred on December 1, 2021. On August 11, 2021, the Company, entered into a fifth amendment to the Technology Square Lease (the “Fifth Amendment”) with ARE-TECH Square, LLC. Under the Fifth Amendment, the Company extended the term of the Technology Square Lease through November 30, 2024 . Under the Fifth Amendment, the Company will continue to pay the landlord the current monthly base rent amount contemplated by the Technology Square Lease through November 30, 2022, with an increase commencing on December 1, 2022 and adjusting the monthly base rent amount to approximately $ 377,000 and an increase commencing on December 1, 2023 and adjusting the monthly base rent amount to approximately $ 388,000 through November 30, 2024. In addition, under the Fifth Amendment, the landlord agreed to provide the Company with a tenant improvement allowance of up to approximately $ 430,000 if requested by the Company by August 11, 2022, subject to specified terms and conditions. In accordance with ASU 2016-02, Leases, or ASC 842, the Company accounted for the Fifth Amendment as a lease modification and remeasured the operating lease liability, resulting in an additional $ 7.0 million operating lease liability and right of use asset. Under the current terms of the Technology Square Lease and Fifth Amendment, the Company does not have any further right to extend the term beyond November 30, 2024. The Company has a $ 0.5 million letter of credit as a security deposit for the Technology Square Lease and has recorded cash held to secure this letter of credit as restricted cash and other assets on the Company's condensed consolidated balance sheets. On August 16, 2019, the Company entered into a lease (the "Hampshire Street Lease") with BMR-Hampshire LLC ("BMR"). The Hampshire Street Lease is for 33,525 rentable square feet of office space in Cambridge, Massachusetts. The Hampshire Street Lease commenced as of December 1, 2019 . The Hampshire Street Lease has an initial term of seven years and four months from the commencement date and provides the Company with an option to extend the lease term for one additional five-year period . After a four-month period during which base rent was not payable, the Hampshire Street Lease provides for monthly rent payments starting at approximately $ 0.2 million and increasing 2.5 % per year. In the event that the Company exercises its option to extend the lease term, the Hampshire Street Lease provides for monthly rent payments during the additional five-year period at the greater of the base rent rate at the end of the initial term or the then-current market rent. The Company has a $ 1.0 million letter of credit in favor of BMR as a security deposit for the Hampshire Street Lease and has recorded cash held to secure this letter of credit as restricted cash and other assets on the Company's condensed consolidated balance sheets. In applying ASC 842, the Company determined the classification of the Hampshire Street Lease to be operating and recorded a lease liability and a right-of-use asset as of December 31, 2019. The Company is required to pay certain variable costs to its landlords in addition to fixed rent. These costs include common area maintenance, real estate taxes, and parking and are included in lease expense. The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the three and six months ended June 30, 2022 and 2021: Three Months Ended Six Months Ended 2022 2021 2022 2021 (in thousands) Lease cost Operating lease cost $ 1,689 $ 1,515 $ 3,378 $ 3,031 Variable lease cost 491 566 933 1,046 Total lease cost $ 2,180 $ 2,081 $ 4,311 $ 4,077 Other information Operating cash flows used for operating leases $ 1,589 $ 1,621 $ 3,216 $ 3,225 Weighted average remaining lease term 3.7 years 4.6 years 3.7 years 4.6 years Weighted average discount rate 9.75 % 9.86 % 9.75 % 9.86 % Future minimum lease payments under the Company’s non-cancelable operating leases as of June 30, 2022, are as follows: (In thousands) 2022 $ 3,361 2023 7,517 2024 7,322 2025 3,057 Thereafter 3,909 Total lease payments $ 25,166 Less: imputed interest ( 4,338 ) Total operating lease liabilities at June 30, 2022 $ 20,828

Collaborations and Licensing Ag

Collaborations and Licensing Agreements	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Collaborations and Licensing Agreements	12. Collaborations and Licensing Agreements HutchMed On August 7, 2021 (the “HutchMed Effective Date”), the Company entered into a strategic collaboration pursuant to a license agreement (the “HutchMed License Agreement”) with Hutchmed Group Investment Limited (formerly known as Hutchison China MediTech Investment Limited) (“HutchMed”), which was amended in May 2022, for the development, manufacture and commercialization of tazemetostat, either as a monotherapy or as a part of combinations with other therapies, including HutchMed proprietary compounds, agreed by the parties under the HutchMed License Agreement (“Licensed Products”) for the treatment of ES, FL, diffuse large B-cell lymphoma in humans, and any additional indications agreed by the parties in accordance with the terms of the HutchMed License Agreement (the “Field”) in mainland China, Taiwan, Hong Kong and Macau (each, a “Jurisdiction”, and collectively, the “Territory”). Agreement Structure The Company has granted HutchMed licenses under patent rights and know-how controlled by the Company to enable HutchMed to develop and commercialize Licensed Products in the Field in the Territory. The licenses granted to HutchMed are co-exclusive with the Company with respect to the development of Licensed Products in the Field in the Territory and exclusive with respect to the commercialization of Licensed Products in the Field in the Territory. The Company also granted HutchMed a license under patent rights and know-how controlled by the Company to enable HutchMed to manufacture tazemetostat drug substance and drug product for the purpose of developing and commercializing Licensed Products in the Field in the Territory. The Company retains development and commercialization rights with respect to Licensed Products in the rest of the world outside of the Territory except for Japan. On May 6, 2022, as contemplated by the HutchMed License Agreement, the Company, Hutchmed Limited (formerly known as Hutchison MediPharma Limited) and Hutchmed (Hong Kong) Limited entered into a manufacturing technology transfer and supply agreement under which the Company has agreed to conduct a technology transfer of manufacturing technology to HutchMed to enable HutchMed to manufacture clinical and commercial quantities of tazemetostat drug substance and drug product to carry out its obligations and exercise its rights under the HutchMed License Agreement. Until the completion of the technology transfer to HutchMed, the Company has agreed to manufacture and supply HutchMed with tazemetostat drug substance and drug product in sufficient quantities for HutchMed’s development and commercialization activities for Licensed Products in the Field in the Territory. HutchMed has agreed to use commercially reasonable efforts to carry out development activities in the Territory as agreed by the parties and to seek to obtain and maintain regulatory approval of the Licensed Products in the Territory. HutchMed has also agreed to use commercially reasonable efforts to commercialize Licensed Products in the Field in the Territory. HutchMed is responsible for all costs it incurs in developing, obtaining regulatory approval of, and commercializing Licensed Products in the Field in the Territory, including costs incurred by HutchMed in conducting clinical trials that only include clinical sites in the Territory. For global studies conducted by the Company that HutchMed elects to participate in by conducting any such study in the Territory, HutchMed will be responsible for enrolling and treating in the Territory 20 % of the total number of study patients of such global study and will be responsible for costs for those patients enrolled and treated in such trials. HutchMed will also be responsible for 20 % of the costs of such global studies that are not specific to any territory and the Company will be responsible for all other costs of such global studies. HutchMed has agreed to participate in the Company’s EZH-301 and SYMPHONY-1 (EZH-302) global studies. Under an amendment to the HutchMed License Agreement executed by the parties on May 6, 2022, HutchMed has responsibility for the SYMPHONY-1 trial in the Territory at HutchMed’s expense, except the Company is responsible for regulatory interactions and filings in mainland China and for the conduct of the SYMPHONY-1 trial in Taiwan, in each case subject to HutchMed’s reimbursement of the Company’s expenses commencing as of the HutchMed Effective Date, and Epizyme has oversight of the conduct of the SYMPHONY-1 trial to ensure consistency with the conduct of the trial globally. Pursuant to the HutchMed License Agreement, the Company received a nonrefundable upfront payment of $ 25.0 million in September 2021. The Company is also entitled to milestone payments of up to $ 110.0 million in the aggregate for achievement of specified development and regulatory milestones with respect to Licensed Products in the Territory, and up to $ 175.0 million in the aggregate for achievement of specified sales milestones in the Territory with respect to the Licensed Products. The Company will also be entitled to receive tiered royalties, ranging from a mid-teens percentage to a low twenties percentage based on HutchMed’s cumulative annual net sales, if any, of Licensed Products in the Territory. Royalties are payable for each Licensed Product commencing on the first commercial sale of the applicable Licensed Product and ending, on a Jurisdiction-by-Jurisdiction basis, on the latest of expiration of specified patent coverage, expiration of specified regulatory exclusivity or a specified period following the first commercial sale in such Jurisdiction and may be reduced in various circumstances. Under the HutchMed License Agreement, the Company issued a warrant to HutchMed (the “HutchMed Warrant”), exercisable at any time prior to August 7, 2025 , for up to 5,653,000 shares of the Company’s common stock at an exercise price of $ 11.50 per share. On September 21, 2021, the Company filed with the SEC a registration statement on Form S-3 registering for resale the shares of the Company’s common stock issuable upon exercise of the HutchMed Warrant in accordance with the HutchMed Warrant. Such registration statement on Form S-3 was declared effective by the SEC on September 29, 2021. Unless earlier terminated, the HutchMed License Agreement will expire upon the expiration of the last royalty term for the last Licensed Product in the Field in the Territory. HutchMed may terminate the HutchMed License Agreement in its entirety for any or no reason upon 12 months’ prior written notice to the Company. Either party may, subject to specified cure periods, terminate the HutchMed License Agreement in the event of the other party’s uncured material breach, and under specified circumstances relating to the other party’s insolvency or if the other party or its affiliates challenges the validity, patentability, or enforceability of patent rights that are owned by or licensed to such party or its affiliates and that are subject to the licenses granted in the HutchMed License Agreement. License Revenue The Company evaluated the terms of the HutchMed License Agreement and first determined that the HutchMed Warrant should be accounted for pursuant to ASC 815, Derivatives and Hedging, with the HutchMed Warrant's fair value of approximately $ 13.0 million (Note 15) at execution considered outside of the revenue arrangement. The Company then evaluated the HutchMed License Agreement under ASC 606, Revenue from Contracts with Customers ("Topic 606") and concluded that the contract counterparty, HutchMed, is a customer. The Company identified the following performance obligations at the inception of the HutchMed License Agreement: (1) exclusive license of rights to develop, manufacture and commercialize tazemetostat in the Territory and (2) research and development services related to global trials. In addition, the Company identified the following customer options that will create manufacturing or supply obligations for the Company upon exercise by HutchMed (1) the supply of tazemetostat, (2) the supply of rituximab, lenalidomide, and placebo and (3) the supply of tazemetostat drug product. The customer options were evaluated as a material right and identified as the third performance obligation. In addition, the Company may also provide certain technology transfer services related to providing HutchMed with the capability to manufacture tazemetostat, for which the Company will receive reimbursement that approximates stand-alone selling price. Under the HutchMed License Agreement, as amended, in order to evaluate the appropriate transaction price, the Company determined that the $ 12.0 million of the up-front fee remaining after allocation to the HutchMed Warrant and the reimbursement to be received for its research and development services constituted the amount of the consideration to be included in the transaction price. Prior to the May 6, 2022 amendment to the HutchMed License Agreement, had the EZH-302 global trial not been deemed a confirmatory trial for purposes of regulatory approval in China, the Company would have been responsible for reimbursing HutchMed for the costs of the portion of the EZH-302 global trial that would be performed in China. The Company had concluded that this potential repayment provision represented variable consideration under the arrangement. Due to the uncertainty of potential repayment, which was based solely on the decision of a regulatory authority, the Company could not assert that it was probable that a significant reversal of revenue would not occur. As a result, the Company determined that the transaction price should be fully constrained. Pursuant to the May 6, 2022 amendment to the HutchMed License Agreement, this potential repayment provision was removed. The Company reevaluated its rights and obligations under the HutchMed License Agreement, as amended, and concluded that the removal of the repayment provision as well as its additional performance obligations with respect to regulatory interactions and filings in mainland China and for the conduct of the SYMPHONY-1 trial in Taiwan represented a modification of the arrangement. Consequently, the Company reassessed its accounting pursuant to the arrangement. The Company determined that the $12.0 million of the up-front fee remaining after allocation to the HutchMed Warrant and the reimbursement to be received for its research and development services constituted the amount of the consideration to be included in the transaction price and to be allocated to the performance obligations. In order to meet the allocation objective under Topic 606, the Company determined that it should allocate to each performance obligation the portion of the transaction price that reflects the amount of consideration the entity expects to be entitled to in exchange for transferring those goods or services to the customer. The Company therefore allocated the variable consideration associated with its research and development services entirely to the research and development performance obligation. The remaining consideration of $ 12.0 million was allocated to the remaining performance obligations – the exclusive license and the material right related to manufacturing obligations, based on the stand-alone selling price for each. For the license, the stand-alone selling price was calculated using an income approach model and included the following key assumptions: the development timeline, discount rate, and probabilities of technical and regulatory success. The value of the material right was determined by calculating the incremental discount provided to HutchMed with respect to its purchases of manufacturing materials. The Company believes that a change in the assumptions used to determine its stand-alone selling price for the license and material right most likely would not have a significant effect on the allocation of consideration received (or receivable) to the performance obligations. The Company concluded that after the amendment, the total transaction price to be allocated to the satisfied performance obligations was $ 17.1 million, which consisted of the license fee and the reimbursement of research and development services. The Company estimated there to be $ 4.0 million of variable consideration allocated to its research and development obligations that will be recognized as such services are performed. None of the development or regulatory milestones have been included in the transaction price, as all such milestone amounts were fully constrained. As part of the Company's evaluation of the constraint, the Company considered numerous factors, including that receipt of the milestones is outside the control of the Company and contingent upon success in future clinical trials and the licensee’s efforts. Any consideration related to sales-based milestones (including royalties) will be recognized when the related sales occur as these amounts have been determined to relate predominantly to the license granted to HutchMed and therefore are recognized at the later of when the performance obligation is satisfied or the related sales occur. The Company will reevaluate the transaction price in each reporting period and as uncertain events are resolved or other changes in circumstance occur. Topic 606 requires the Company to select a single revenue recognition method for the performance obligation that depicts the Company’s performance in transferring control of services or goods. Accordingly, the Company recognized the revenue from the license at a point in time as the licenses associated with the license performance obligation have significant standalone functionality that HutchMed can immediately use. The licenses were delivered in the third quarter of 2021. Therefore, the promise to provide a customer with a right to use the Company's intellectual property would indicate revenue is satisfied at a point in time. For the research and development performance obligation, the Company utilizes a cost-based input method to measure proportional performance and to calculate the amount of revenue to recognize. The Company believes that this is the best measure of progress because it reflects the manner in which the Company transfers its performance obligation to HutchMed. The Company recognizes the amount allocated to the material right associated with manufacturing materials as revenue based on the output method as HutchMed exercises its options and the manufacturing materials are transferred to HutchMed. During the second quarter of 2022, the Company allocated $ 11.8 million of the transaction price to the license and recognized this amount as revenue during the second quarter of 2022. Consideration allocated to the research and development performance obligation was $ 4.7 million, of which $ 0.8 million was recognized during the second quarter of 2022. Revenue allocated to the material right was $ 0.6 million, $ 0.1 million of which was recognized during the second quarter of 2022. In addition, HutchMed made manufacturing material purchases of $ 3.8 million during the second quarter of 2022, which were recognized upon delivery. GSK In January 2011, the Company entered into a collaboration and license agreement (the “GSK Collaboration and License Agreement”) with Glaxo Group Limited (an affiliate of GlaxoSmithKline plc) (“GSK”), to discover, develop and commercialize novel small molecule histone methyltransferase ("HMT") inhibitors directed to available targets from the Company’s platform. Under the terms of the GSK Collaboration and License Agreement, the Company granted GSK exclusive worldwide license rights to HMT inhibitors directed to three targets. In March 2014, the Company and GSK amended certain terms of this agreement for the third licensed target, revising the license terms with respect to candidate compounds and amending the corresponding financial terms, including reallocating milestone payments and increasing royalty rates as to the third target. Subsequent to a GSK strategic portfolio prioritization, the Company received notice in October 2017 that GSK terminated the agreement with respect to the third target, effective December 31, 2017, which returned all rights to that target to the Company. On December 16, 2021, the Company received written notice from GSK that GSK elected to terminate the GSK Collaboration and License Agreement without cause, and in accordance with the terms of the agreement and the notice of termination, the termination became effective as of March 16, 2022. As a result of the termination of the agreement, as of the termination effective date, the license rights granted by the Company to GSK terminated, and GSK ceased to accrue any financial obligations to the Company and the Company is entitled to pursue PRMT5 and PRMT1 targets in all fields worldwide without further obligation to GSK. The Company substantially completed all of its obligations under this agreement by the end of 2015. The termination of the agreement had no impact on the Company’s financial statements. Eisai In April 2011, the Company entered into a collaboration and license agreement with Eisai, under which the Company granted Eisai an exclusive worldwide license to its small molecule HMT inhibitors directed to the EZH2 HMT, including the Company’s product candidate tazemetostat, while retaining an opt-in right to co-develop, co-commercialize and share profits with Eisai as to licensed products in the United States. In March 2015, the Company entered into an amended and restated collaboration and license agreement with Eisai (the “Eisai License Agreement”), under which the Company reacquired worldwide rights, excluding Japan, to its EZH2 program, including tazemetostat. Under the Eisai License Agreement, the Company is responsible for global development, manufacturing and commercialization outside of Japan of tazemetostat and any other EZH2 product candidates, with Eisai retaining development and commercialization rights in Japan, as well as a right to elect to manufacture tazemetostat and any other EZH2 product candidates in Japan, and a right of first negotiation for the rest of Asia. Eisai waived its right of first negotiation for the rest of Asia in 2018. In March 2021, the Company and Eisai entered into a supply agreement providing for the manufacture and supply to Eisai of tazemetostat drug product. Under the terms of the supply agreement, the Company also agreed to waive its right of exclusive supply of tazemetostat drug substance from the Company’s drug substance manufacturer. The Company deferred $ 5.0 million of revenue allocated to the Company’s waiver of its exclusive right to supply of tazemetostat drug substance as of March 31, 2021, which was recognized in April 2021 upon delivery of the Company's waiver to the drug substance manufacture. During the three and six months ended June 30, 2021, the Company recognized $ 5.0 million and $ 6.3 million, respectively, related to the Company's waiver of its exclusive right to supply of tazemetostat drug substance from the Company's drug substance manufacturer and delivery of tazemetostat drug product in collaboration and other revenue. As of June 30, 2022 and December 31, 2021 , the Company had accounts receivable of less than $ 0.1 million for both periods, due from Eisai. During the three and six months ended June 30, 2022, the Company recorded $ 1.3 million and $ 2.6 million, respectively , related to the worldwide royalties due under the Eisai License Agreement in cost of revenue based on U.S. sales of TAZVERIK. During the three and six months ended June 30, 2021, the Company recorded $ 1.2 million and $ 2.1 million, respectively, related to the worldwide royalties due under the Eisai License Agreement in cost of revenue based on U.S. sales of TAZVERIK. As of June 30, 2022 and 2021 , $ 1.3 million and $ 1.2 million, respectively, in royalties were payable under the Eisai License Agreement. F or additional information regarding certain of the Eisai royalties, see Note 13, Sale of Future Royalties . Roche In December 2012, Eisai and the Company entered into a companion diagnostics agreement with Roche Molecular Systems, Inc. (“Roche Molecular”), under which Eisai and the Company engaged Roche Molecular to develop a companion diagnostic to identify patients who possess certain activating mutations of EZH2. In October 2013, this agreement was amended to include additional mutations in EZH2. The development costs due under the amended agreement with Roche Molecular were the responsibility of Eisai until the execution of the amended and restated collaboration and license agreement with Eisai in March 2015, at which time the Company assumed responsibility for the remaining development costs due under the agreement. In December 2015, the Company and Eisai entered into a second amendment to the companion diagnostics agreement with Roche Molecular. The agreement was further amended in March 2018. Under the amended agreement, the Company was responsible for remaining development costs of $ 10.4 million due under the agreement as of March 2018 and Eisai agreed to reimburse the Company $ 0.9 million of this amount related to a regulatory milestone for Japan. In July 2019, the Company entered into a fourth amendment to the companion diagnostics agreement. Under the amended agreement, the Company and Roche Molecular agreed to divide a $ 1.0 million regulatory milestone for the United States into two separate milestone payments, of which $ 0.5 million was paid by the Company as part of the signed amendment, and the remaining $ 0.5 million was paid by the Company in December 2019 upon the satisfaction of certain conditions set forth in the fourth amendment to the companion diagnostics agreement. As part of this fourth amendment, Roche Molecular also assigned all of its rights and obligations under the companion diagnostics agreement to Roche Sequencing Solutions (“Roche Sequencing”) due to an internal reorganization, and this assignment became effective as of January 1, 2020. As of June 30, 2022 , the Company is responsible for the remaining development costs of $ 1.0 million due under the agreement. The $ 0.9 million that Eisai agreed to reimburse the Company related to a regulatory milestone for Japan was achieved as of June 30, 2020 and the payment was received in the fourth quarter of 2020. In addition, the Company paid $ 1.0 million for the achievement of a development milestone in the fourth quarter of 2020. Under the agreement with Roche Sequencing, Roche Sequencing is obligated to use commercially reasonable efforts to develop and to make commercially available the companion diagnostic. Roche Sequencing has exclusive rights to commercialize the companion diagnostic. On June 18, 2020, the FDA approved the companion diagnostic that is intended to identify FL patients with an EZH2 mutation for treatment with tazemetostat. The agreement with Roche Sequencing will expire when the Company and Eisai are no longer developing or commercializing tazemetostat. The Company and Eisai may terminate the agreement by giving Roche Sequencing 90 days’ written notice if the Company and Eisai discontinue development and commercialization of tazemetostat or determine, in conjunction with Roche Sequencing, that the companion diagnostic is not needed for use with tazemetostat. Any party may also terminate the agreement in the event of a material breach by any party, in the event of material changes in circumstances that are contrary to key assumptions specified in the agreement or in the event of specified bankruptcy or similar circumstances. Under specified termination circumstances, Roche Sequencing may become entitled to specified termination fees.

Sale of Future Royalties

Sale of Future Royalties	6 Months Ended
	Jun. 30, 2022
Deferred Revenue Disclosure [Abstract]
Sale of Future Royalties	13. Sale of Future Royalties On November 4, 2019, the Company entered into a loan agreement with BioPharma Credit PLC (the “Collateral Agent”), and the Lenders (as defined therein), providing for up to $ 70.0 million in secured term loans to be advanced in up to three tranches (the “Loan Agreement”). As of June 30, 2020, the Company had borrowed an aggregate principal amount under the first tranche of $ 25.0 million (the “Tranche A Note Payable”), the second tranche of $ 25.0 million (the “Tranche B Note Payable”), and the third tranche of $ 20.0 million (the “Tranche C Note Payable”) under the Loan Agreement. On November 3, 2020, the Company, the Collateral Agent and the Lenders amended and restated the Loan Agreement, (as amended and restated, the “Amended and Restated Loan Agreement”), to provide for, among other things, an additional secured term loan of $ 150.0 million, or the Tranche D Loan. On November 18, 2020, the Company borrowed the Tranche D Loan (see Note 14, Long-Term Debt ). The Company paid a commitment fee of 2.00 % of the original $ 70.0 million committed facility amount in November 2019 and 2 % of the $ 150.0 million Tranche D Loan in November 2020, as well as expenses incurred by the Lender in executing the agreements. The interest rate for the Tranche D Loan will be determined by reference to a Eurodollar rate plus 7.75 % above such Eurodollar rate. The Eurodollar rate will have a 2.00 % floor. The Tranche D Loan will be due in eight equal quarterly principal payments commencing on the 51st month anniversary of the date on which the Lenders fund the Tranche D Loan. All unpaid principal and interest under the Tranche D Loan will be due and payable on the 72nd month anniversary of the date on which the Lenders funded the Tranche D Loan. On November 4, 2019, the Company also executed a purchase agreement (the “RPI Purchase Agreement”) with RPI. Pursuant to the RPI Purchase Agreement, the Company agreed to sell to RPI 6,666,667 shares of its common stock, a warrant to purchase up to 2,500,000 shares of common stock at an exercise price of $ 20.00 per share (the “Common Stock Warrant”), and all of the Company’s rights to receive royalties from Eisai with respect to net sales by Eisai of tazemetostat products in Japan pursuant to the Eisai License Agreement and any successor arrangement for Japan sales (the “Japan Royalty”, and collectively, the “Transaction”). In consideration for the sale of shares of common stock, the Common Stock Warrant and the Japan Royalty, RPI paid the Company $ 100.0 million upon the closing of the RPI Purchase Agreement. In addition, RPI agreed, in connection with RPI’s acquisition from Eisai of the right to receive royalties from the Company under the Eisai License Agreement, to reduce the Company’s royalty obligation by low single digits upon the achievement of specified annual net sales levels over $ 1.5 billion. In addition, under the RPI Purchase Agreement, the Company had the right to sell, and RPI had the obligation to purchase, subject to certain conditions, including a maximum purchase price of $ 20.00 per share, $ 50.0 million of shares of common stock at the Company’s option for an 18-month period from the date of execution of the RPI Purchase Agreement (the “Put Option”). In February 2020, the Company sold 2.5 million shares of its common stock to RPI, for an aggregate of $ 50.0 million in proceeds pursuant to the Put Option. Additionally, under the terms of the RPI Purchase Agreement, the founder and chief executive officer of RP Management, an affiliate of RPI, and a co-founder of Pharmakon Advisors LP, an affiliate of the Lenders, was elected as a director of the Company. As of June 30, 2022 and December 31, 2021 , RPI and its affiliates owned approximately 18.9 % and 8.6 % of the Company’s common stock, respectively. The Company accounted for the Loan Agreement and RPI Purchase Agreement as a single arrangement as RPI and the Lenders are related parties and the agreements were negotiated together. The aggregate proceeds of $ 125.0 million were allocated on a relative fair value basis, which approximated their respective actual fair values, to the four units of accounting pursuant to the transaction as follows: (1) $ 79.0 million to the common stock issued to RPI based on the closing price of the Company’s common stock on the date of the transaction, (2) $ 8.4 million to the Common Stock Warrant to purchase shares of common stock, based on the Black-Scholes option pricing model, (3) $ 12.6 million to the liability related to the sale of future royalties based on a discounted cash flow model and (4) $ 25.0 million to the Tranche A Note Payable based on the terms of the Loan Agreement. Transaction costs of $ 2.0 million were allocated directly to the units of accounting it relates to. Although the Company sold all of its rights to receive the Japan Royalty, under the terms of the RPI Agreement, the Company continues to own all tazemetostat intellectual property rights and at execution had significant continuing involvement in the generation of these royalties. Due to the Company’s continuing involvement, the Company will continue to account for any royalties due as revenue and recorded the proceeds from this transaction as a liability (“Royalty Obligation”) that will be accreted using the effective interest method over the estimated life of the RPI Purchase Agreement. As royalties are remitted to RPI from Eisai, the balance of the Royalty Obligation will be effectively repaid over the life of the Eisai License Agreement. In order to determine the accretion of the Royalty Obligation, the Company is required to estimate the total amount of future royalty payments to RPI over the life of the Eisai License Agreement. The $ 12.6 million recorded at execution will be accreted to the total of these royalty payments as interest expense over the life of the Royalty Obligation. At execution, the Company’s estimate of this total interest expense resulted in an effective annual interest rate of approximately 9.01 %. This estimate contains significant assumptions that impact both the amount recorded at execution and the interest expense that will be recognized over the royalty period. The Company periodically assesses the estimated royalty payments to RPI from Eisai and to the extent the amount or timing of such payments is materially different than the original estimates, an adjustment is made to the effective interest rate, which will be recorded prospectively to increase or decrease interest expense. There are a number of factors that could materially affect the amount and timing of royalty payments to RPI from Eisai, and correspondingly, the amount of interest expense recorded by the Company, most of which are not within the Company’s control. Such factors include, but are not limited to, delays or discontinuation of development of tazemetostat in Japan, regulatory approval, changing standards of care, the introduction of competing products, manufacturing or other delays, generic competition, intellectual property matters, adverse events that result in governmental health authority imposed restrictions on the use of the drug products, significant changes in foreign exchange rates as the royalties remitted to RPI are made in U.S. dollars (USD) while the underlying Japan sales of tazemetostat will be made in currencies other than USD, and other events or circumstances that are not currently foreseen as tazemetostat is still under development in Japan and subject to regulatory approval. Changes to any of these factors could result in increases or decreases to both royalty revenues and interest expense. On June 23, 2021, Eisai announced that it had obtained manufacturing and marketing approval for the EZH2 inhibitor “Tazverik® Tablets 200 mg” (tazemetostat hydrobromide) in Japan with the indication of relapsed or refractory EZH2 gene mutation-positive FL (only when standard treatment is not applicable), which caused the Company to reassess the estimated future royalty payments to RPI. As of June 30, 2022 , the Company’s assessment of the estimated future royalty payments to RPI resulted in a current effective interest rate of approximately 9.2 %. The following table shows the activity of the Royalty Obligation since the transaction inception through June 30, 2022: As of June 30, 2022 (In thousands) Proceeds from sale of future royalties $ 12,601 Non-cash royalty revenue ( 93 ) Non-cash interest expense recognized 4,104 Liability related to the sale of future royalties - ending balance $ 16,612 Less current portion ( 592 ) Related party liability related to sale of future royalties, net of current portion $ 16,020 During the three months and six months ended June 30, 2022, the Company recorded $ 40.0 thousand and $ 66.0 thousand, respectively, in non-cash royalties from net sales of tazemetostat in Japan. During the three and six months ended June 30, 2021, no non-cash royalties from net sales of tazemetostat in Japan were recorded. During the three and six months ended June 30, 2022, the Company recor ded $ 0.4 and $ 0.7 million, respectively, of related non-cash interest expense. During the three and six months ended June 30, 2021, the Company recor ded $ 0.5 and $ 0.9 million, respectively, of related non-cash interest expense.

Long-Term Debt

Long-Term Debt	6 Months Ended
	Jun. 30, 2022
Debt Disclosure [Abstract]
Long-Term Debt	14. Long-Term Debt On November 4, 2019, the Company entered into the Loan Agreement, which provided for up to $ 70.0 million in secured term loans to be advanced in up to three tranches. The Company borrowed $70.0 million in the aggregate under the three tranches pursuant to the Loan Agreement. With the FDA’s June 2020 approval of tazemetostat for the treatment of FL in the United States, the Company also had the right, but not the obligation, to request up to an additional $ 300.0 million in secured term loans, subject to the approval of the Lenders, provided the Company had not prepaid any outstanding term loans at the time of such request and such request was made before November 18, 2021. On November 3, 2020, the Company entered into the Amended and Restated Loan Agreement with the Lenders. The Amended and Restated Loan Agreement provides for, among other things, an additional secured term loan of $ 150.0 million, or the Tranche D Loan. On November 3, 2020, the Company also delivered written notice to the Lenders to draw down the Tranche D Loan, which was funded on November 18, 2020. The Company paid a commitment fee of 2.00 % of the original $ 70.0 million committed facility amount in November 2019 and 2 % of the $ 150.0 million Tranche D Loan in November 2020, as well as expenses incurred by the Lender in executing the agreements. The interest rate for the Tranche D Loan will be determined by reference to a Eurodollar rate plus 7.75 % above such Eurodollar rate. The Eurodollar rate will have a 2.00 % floor. The Tranche D Loan will be due in eight equal quarterly principal payments commencing on the 51st month anniversary of the date on which the Lenders fund the Tranche D Loan. All unpaid principal and interest under the Tranche D Loan will be due and payable on the 72nd month anniversary of the date on which the Lenders funded the Tranche D Loan. The Amended and Restated Loan Agreement also amended the payment period principal and interest for the first three tranches of term loans. Under the original terms, the Company was required to make interest only payments on the outstanding obligation through February 28, 2023, and thereafter eight quarterly payments of principal and interest. Under the amended and restated terms, the Company is required to make interest only payments on the $ 70.0 million outstanding obligation through November 2023, and thereafter four quarterly payments of principal and interest. All unpaid principal and interest on the $ 70.0 million borrowed under the original Loan Agreement is due and payable in November 2024, the 60th month anniversary of the date on which the Lenders funded the first tranche of term loans. The interest rates for the existing tranches of term loans remain unchanged and will continue to be determined by reference to a Eurodollar rate plus 7.75% above such Eurodollar rate. The Eurodollar rate will have a 2.00% floor. Each of the four term loans may be prepaid before maturity in whole or in part, however there is a $ 50.0 million minimum prepayment for any prepayment of the loans. If the Company prepays any tranche of term loans, in whole or in part, during the first 36 months from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to the greater of (x) a make-whole amount equal to the interest that would have accrued on the principal amount to be prepaid and (y) a premium equal to 0.03 multiplied by the principal amount to be prepaid. If the Company prepays a tranche of term loan, in whole or in part, between the 36th month and 48th month from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to 0.02 multiplied by the principal amount to be prepaid. If the Company prepays a tranche of term loans, in whole or in part, between the 48th month and 60th month from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to 0.01 multiplied by the principal amount to be prepaid. The Amended and Restated Loan Agreement was accounted for as a debt modification based on a comparison of the present value of the cash flows under the terms of the debt immediately before and after the effective date of The Amended and Restated Loan Agreement, which resulted in a change of less than 10%. As a result, issuance costs paid to the Lenders in connection with The Amended and Restated Loan Agreement were recorded as a reduction of the carrying amount of the debt liability and unamortized issuance costs as of the date of the modification are amortized to interest expense over the repayment term of The Amended and Restated Loan Agreement. The obligations under the Amended and Restated Loan Agreement, including the Company’s payment obligations in respect of the Tranche D Loan are secured by the first priority security interest in and a lien on substantially all of the assets of the Company, subject to certain exceptions, that the Company granted to the Lenders in connection with the first tranche of term loans under the Loan Agreement. The Amended and Restated Loan Agreement contains certain customary representations and warranties, affirmative and negative covenants and events of default applicable to the Company and its subsidiaries. If an event of default occurs and is continuing, the Collateral Agent may, among other things, accelerate the loans and foreclose on the collateral. The Company has determined that the risk of subjective acceleration under the material adverse events clause is not probable and therefore has classified the outstanding principal in non-current liabilities based on scheduled principal payments. The Company has the following minimum aggregate future loan payments at June 30, 2022 : As of June 30, 2022 (In thousands) 2022 $ — 2023 — 2024 70,000 2025 75,000 2026 75,000 Total minimum payments 220,000 Less amounts representing interest and discount ( 3,115 ) Less current portion — Long-term debt, net of current portion $ 216,885 For the three and six months ended June 30, 2022 and 2021, interest expense related to the Company's Amended and Restated Loan Agreement was approximately $ 5.4 million and $ 10.8 million, respectively, in both periods. The total carrying value of debt is classified as long-term on the Company's condensed consolidated balance sheet as of June 30, 2022 and December 31, 2021.

Stockholders' (Deficit) Equity

Stockholders' (Deficit) Equity	6 Months Ended
	Jun. 30, 2022
Equity [Abstract]
Stockholders' (Deficit) Equity	15. Stockholders’ (Deficit) Equity Common Stock On April 8, 2021, the Company’s board of directors adopted, subject to stockholder approval, an amendment to the Company’s Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 150,000,000 to 225,000,000 (the "2021 Charter Amendment"). At the Company’s 2021 Annual Meeting of Stockholders, the stockholders of the Company approved the 2021 Charter Amendment, which was filed with the Secretary of State of the State of Delaware on June 11, 2021. The number of authorized shares of preferred stock was not affected by the 2021 Charter Amendment. On March 16, 2022, the Company’s board of directors adopted, subject to stockholder approval, a proposed amendment to the Company’s Restated Certificate of Incorporation to increase the number of authorized shares of common stock from 225,000,000 to 450,000,000 (the "2022 Charter Amendment"). At the Company’s 2022 Annual Meeting of Stockholders, the stockholde rs of the Company approved the 2022 Charter Amendment, which was filed with the Secretary of State of the State of Delaware on May 17, 2022. The number of authorized shares of preferred stock was not affected by the 2022 Charter Amendment. Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to dividends when and if declared by the board of directors. In January 2022, the Company raised approximately $ 79.5 million in net proceeds (after deducting underwriting discounts and commissions and estimated offering costs but excluding any expenses and other costs reimbursed by the underwriters) from the sale of 56,666,667 shares of its common stock in a public offering at a price of $ 1.50 per share. 2021 At-the-Market Offering Program On May 6, 2021, the Company entered into an Open Market Sale Agreement SM (“ATM Sale Agreement”), with Jefferies LLC (“Jefferies”) to sell, from time to time, shares of the Company's common stock having an aggregate offering price of up to $ 200.0 million through an “at the market offering” as defined in Rule 415 under the Securities Act of 1933, as amended, under which Jefferies would act as sales agent (the "ATM Offering"). The shares that may be sold under the ATM Sale Agreement, if any, are issued and sold pursuant to the Company’s shelf registration statement on Form S -3 that was declared effective by the Securities and Exchange Commission on May 13, 2021. The Company agreed to compensate Jefferies at a fixed commission rate equal to 3.0 % of the gross sales proceeds of such shares. From the initiation of the ATM Offering through June 30, 2022 , the Company has issued and sold 5,314,135 shares under the ATM Sale Agreement, resulting in aggregate net proceeds of $ 18.3 million after deducting issuance costs of $ 0.6 million. During the three months ended June 30 2022, there were no sales of the Company's common stock under the ATM Sale Agreement. During the six months ended June 30, 2022 , the Company sold a total of 1,473,158 shares of the Company's common stock under the ATM Sale Agreement, at a volume weighted average gross selling price of approximately $ 1.82 per share for net proceeds of approximately $ 2.4 million. Convertible Preferred Stock The Company had no shares of Series A Preferred Stock outstanding as of June 30, 2022. The Company had 337,800 shares of Series A Preferred Stock outstanding as of December 31, 2021. Voting Rights Shares of Series A Preferred Stock will generally have no voting rights except as required by law and except that the consent of the holders of a majority of the outstanding shares of Series A Preferred Stock will be required to amend the terms of the Series A Preferred Stock or take certain other actions with respect to the Series A Preferred Stock. Dividends Shares of Series A Preferred Stock will be entitled to receive dividends equal to (on an as-if-converted-to-common stock basis), and in the same form and manner as, dividends actually paid on shares of the Company’s common stock. Liquidation Rights Subject to the prior and superior rights of the holders of any senior securities of the Company, upon liquidation, dissolution or winding up of the Company, whether voluntary or involuntary, each holder of shares of Series A Preferred Stock shall be entitled to receive, in preference to any distributions of any of the assets or surplus funds of the Company to the holders of common stock, an amount equal to $ 0.001 per share of Series A Preferred Stock, plus an additional amount equal to any dividends declared but unpaid on such shares, before any payments shall be made or any assets distributed to holders of any class of common stock. If, upon any such liquidation, dissolution or winding up of the Company, the assets of the Company shall be insufficient to pay the holders of shares of the Series A Preferred Stock the amount required under the preceding sentence, then all remaining assets of the Company shall be distributed ratably to holders of the shares of the Series A Preferred Stock in proportion to the respective amounts which would otherwise be payable in respect of the shares held by them upon such distribution if all amounts payable on or with respect to such shares were paid in full. Conversion Each share of Series A Preferred Stock shall be convertible, at any time and from time to time from and after the issuance date, at the option of the holder thereof, into a number of shares of common stock equal to 10 shares of common stock, provided that the holder will be prohibited from converting Series A Preferred Stock into shares of the Company’s common stock if, as a result of such conversion, the holder, together with its affiliates and attribution parties, would own more than 9.99 % of the total number of shares of common stock then issued and outstanding. The holder can change this requirement to a higher or lower percentage, not to exceed 9.99 % of the number of shares of common stock outstanding, upon 61 days’ notice to the Company. In February 2020, 12,200 shares of Series A Preferred Stock were converted to 122,000 shares of common stock. In May 2022, 337,800 shares of Series A Preferred Stock were converted to 3,378,000 shares of common stock. Redemption The Company is not obligated to redeem or repurchase any shares of Series A Preferred Stock. Shares of Series A Preferred Stock are not entitled to any redemption rights or mandatory sinking fund or analogous fund provisions. Warrants In November 2019, the Company issued the Common Stock Warrant for the purchase of up to 2,500,000 shares of Common Stock at an exercise price of $ 20.00 per share to RPI pursuant to the RPI Purchase Agreement (for additional information see Note 13, Sale of Future Royalties ), which was classified as equity and recorded at its relative fair value of $ 8.4 million to additional paid-in capital on the Company's condensed consolidated balance sheets. The Common Stock Warrant remains outstanding as of June 30, 2022. In August 2021, the Company issued the HutchMed Warrant to HutchMed under the HutchMed License Agreement, exercisable at any time prior to August 7, 2025, for up to 5,653,000 shares of the Company’s common stock at an exercise price of $ 11.50 per share. Under the HutchMed Warrant, the number of shares issuable under the warrant is reduced from 5,653,000 to 2,826,500 in the event that the HutchMed License Agreement is terminated for certain reasons as more fully described in the HutchMed License Agreement. Due to this provision in the HutchMed Warrant, the Company concluded that the warrant does not meet the exception from derivative accounting pursuant to ASC 815, Derivatives and Hedging, which requires that the warrant be accounted for as a derivative. Accordingly, the Company recorded a warrant liability in the amount of approximately $ 13.0 million upon issuance of the HutchMed Warrant. The fair value of the HutchMed Warrant was determined using a Black-Scholes and Monte Carlo pricing model. The HutchMed Warrant is subject to revaluation at each balance sheet date and any changes in fair value are recorded as a non-cash gain or (loss) in the Company's condensed consolidated statement of operations and comprehensive loss as a component of other income (expense), net until the earlier of the exercise or expiration of the HutchMed Warrant or upon the completion of a liquidation event. Upon exercise, the HutchMed Warrant is subject to revaluation just prior to the date of the warrant exercise and any changes in fair value are recorded as a non-cash gain or (loss). The Company recorded non-cash gains of approximately $ 1.4 million during the six months ended June 30, 2022 in its condensed consolidated statement of operations and comprehensive loss attributable to the decreases in the fair value of the warrant liability that resulted from a reduction in the Company's stock price as of June 30, 2022. The following table rolls forward the fair value of the HutchMed Warrant liability, the fair value of which is determined by Level 3 inputs at inception on August 7, 2021, and as of June 30, 2022: (In thousands) Fair value at January 1, 2022 $ 1,930 Decrease in fair value ( 1,350 ) Fair value at June 30, 2022 $ 580 The key assumptions used to value the HutchMed Warrant were as follows: Inception As of June 30, 2022 Risk-free interest rate 0.6 % 2.99 % Expected term (in years) 4.0 years 3.11 years Expected volatility of underlying stock 70.0 % 88.3 % Expected dividend yield — — Stock price $ 6.47 $ 1.47

Stock-Based Compensation

Stock-Based Compensation	6 Months Ended
	Jun. 30, 2022
Share-based Payment Arrangement [Abstract]
Stock-Based Compensation	16. Stock-Based Compensation On March 11, 2022, upon the recommendation of the compensation committee of the Company’s board of directors, and subject to stockholder approval, the Company’s board of directors adopted the 2022 Equity Incentive Plan. At the Company’s 2022 Annual Meeting of Stockholders on May 17, 2022, the stockholders of the Company approved the 2022 Equity Incentive Plan, which replaces the Company’s 2013 Stock Incentive Plan. Following approval of the 2022 Equity Incentive Plan, no additional awards may be made under the 2013 Stock Incentive Plan. The Company also maintains the 2013 Employee Stock Purchase Plan. At the Company’s 2022 Annual Meeting of Stockholders on May 17, 2022, the stockholders of the Company also approved an amendment to the 2013 Employee Stock Purchase Plan to eliminate the annual “evergreen” provision and authorize an aggregate of 2,500,000 shares of the Company’s common stock for issuance under such plan. Such amendment will become effective as of September 1, 2022. In addition, during the year ended December 31, 2021, the Company granted options to purchase an aggregate of 248,366 shares of the Company's common stock and 106,955 restricted stock units (RSUs) to four new employees as equity inducement awards outside of the Company's 2013 Stock Incentive Plan and material to the employees’ acceptance of employment with the Company. These options have a weighted average exercise price of $ 5.12 per share, and the RSUs have a weighted average grant date fair value of $ 5.08 per unit. On April 1, 2022, the Company granted options to purchase an aggregate of 800,000 shares of the Company's common stock to a new employee as equity inducement awards outside of the Company's 2013 Stock Incentive Plan and material to the employee’s acceptance of employment with the Company. These options have an exercise price of $ 1.14 per share, which is equal to the closing price of the Company's common stock on April 1, 2022, the grant date of these options. These equity inducement awards were approved in accordance with Nasdaq Listing Rule 5635(c)(4), and these equity inducement awards remained outstanding as of June 30, 2022. These equity inducement awards are included in stock-based compensation expense and the following tables. Total stock-based compensation expense related to stock options, restricted stock units, shares issued under the 2013 Employee Stock Purchase Plan, and shares of common stock issued to non-employee directors in lieu of board and board committee fees was $ 4.5 million and $ 6.7 million for the three months ended June 30, 2022 and 2021, respectively, and $ 9.7 million and $ 13.7 million for the six months ended June 30, 2022 and June 30, 2021, respectively. Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended Six Months Ended June 30, 2022 2021 2022 2021 (In thousands) (In thousands) Research and development $ 1,417 $ 2,023 $ 3,209 $ 4,253 General and administrative 3,034 4,695 6,531 9,480 Total $ 4,451 $ 6,718 $ 9,740 $ 13,733 Stock Options The weighted-average grant date fair value of options, estimated as of the grant date using the Black-Scholes option pricing model, was $ 0.84 and $ 5.10 per option for those options granted during the six months ended June 30, 2022 and June 30, 2021, respectively. Key assumptions used to apply this pricing model were as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 Risk-free interest rate 2.7 % 0.8 % 2.2 % 0.5 % Expected life of options 5.87 years 5.71 years 5.94 years 5.94 years Expected volatility of underlying stock 74.2 % 70.7 % 73.1 % 70.5 % Expected dividend yield 0.0 % 0.0 % 0.0 % 0.0 % The following is a summary of stock option activity for the six months ended June 30, 2022: Number of Weighted Weighted Aggregate (In thousands) (In years) (In thousands) Outstanding at December 31, 2021 12,946 $ 11.61 Granted 5,681 1.29 Exercised — — Forfeited ( 3,204 ) 11.26 Outstanding at June 30, 2022 15,423 $ 7.87 8.06 $ 1,073 Exercisable at June 30, 2022 5,525 $ 13.85 5.95 $ — As of June 30, 2022, there wa s $ 23.8 million of unrecognized compensation cost related to stock options that are expected to vest. These costs are expected to be recognized over a weighte d average remaining vesting period of 2.71 y ears. Restricted Stock Units During the six months ended June 30, 2022 , 87,500 RSUs were granted to an executive (the “executive RSUs”) and 80,946 RSUs were granted to non-employee directors (the “non-employee RSUs”). RSUs vest based on continuing service to the Company. Assuming all service conditions are achieved, the executive RSUs will vest in three equal installments with the first installment vesting approximately six and a half months following the grant date and the second and third installments vesting annually thereafter, and the non-employee director RSUs will vest as to 100 % of the RSUs on the earlier of the first anniversary of the grant date and the date of the succeeding annual meeting of stockholders. Number Weighted Outstanding at December 31, 2021 2,222 $ 8.70 Granted 169 1.00 Vested ( 361 ) 12.57 Forfeited ( 537 ) 7.62 Outstanding at June 30, 2022 1,493 $ 7.28 Compensation expense totaling $ 1.1 million and $ 2.3 million was recognized for the RSUs for the three and six months ended June 30, 2022, respectively. Compensation expense totaling $ 1.2 million and $ 2.2 million was recognized for the RSUs for the three and six months ended June 30, 2021, respectively. As of June 30, 2022 , there was $ 8.0 million of unrecognized compensation cost related to RSUs that are expected to vest. These costs are expected to be recognized over a weighted average remaining vesting period of 1.72 years.

Loss Per Share

Loss Per Share	6 Months Ended
	Jun. 30, 2022
Earnings Per Share [Abstract]
Loss Per Share	17. Loss Per Share Basic and diluted loss per share allocable to common stockholders are computed as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 (In thousands except per share data) (In thousands except per share data) Net loss $ ( 35,744 ) $ ( 64,363 ) $ ( 91,249 ) $ ( 134,637 ) Weighted average shares outstanding 166,990 102,053 155,658 101,922 Basic and diluted loss per share allocable to common stockholders $ ( 0.21 ) $ ( 0.63 ) $ ( 0.59 ) $ ( 1.32 ) The following common stock equivalents were excluded from the calculation of diluted loss per share allocable to common stockholders because their inclusion would have been anti-dilutive: As of June 30, 2022 2021 (In thousands) Stock options 15,423 12,058 Restricted stock units 1,493 1,358 Shares issuable under employee stock purchase plan 83 113 Series A Preferred Stock (if converted) — 3,378 Warrants 8,153 2,500 25,152 19,407

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2022
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The condensed consolidated financial statements of the Company included herein have been prepared, without audit, pursuant to the rules and regulations of the SEC. Certain information and footnote disclosures normally included in financial statements prepared in accordance with accounting principles generally accepted in the United States have been condensed or omitted from this report, as is permitted by such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the fiscal year ended December 31, 2021, or the Annual Report. The unaudited condensed consolidated financial statements include the accounts of Epizyme, Inc. and its wholly owned, controlled subsidiary, Epizyme Securities Corporation. All intercompany transactions and balances of subsidiaries have been eliminated in consolidation. In the opinion of management, the information furnished reflects all adjustments, all of which are of a normal and recurring nature, necessary for a fair presentation of the results for the reported interim periods. The Company considers events or transactions that occur after the balance sheet date but before the condensed consolidated financial statements are issued to provide additional evidence relative to certain estimates or to identify matters that require additional disclosure. The three months ended June 30, 2022 and 2021 are referred to as the second quarter of 2022 and 2021 , respectively. The results of operations for interim periods are not necessarily indicative of results to be expected for the full year or any other interim period.
Use of Estimates	Use of Estimates The preparation of these condensed consolidated financial statements in accordance with accounting principles generally accepted in the United States requires management to make estimates, judgments and assumptions that affect the reported amounts of assets and liabilities and disclosures of contingent assets and liabilities, as of the date of the condensed consolidated financial statements, and the reported amounts of revenue and expenses during the reporting period. Actual results and outcomes may differ materially from management’s estimates, judgments and assumptions.
Significant Accounting Policies	Significant Accounting Policies The significant accounting policies used in preparation of these condensed consolidated financial statements for the three and six months ended June 30, 2022 are consistent with those discussed in Note 2 to the consolidated financial statements in the Annual Report and are updated below as necessary.
Going Concern	Going Concern At each reporting period, the Company evaluates whether there are conditions or events that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. The Company is required to make certain additional disclosures if it concludes substantial doubt exists about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued and such doubt is not alleviated by the Company’s plans or when the Company's plans alleviate substantial doubt about the Company’s ability to continue as a going concern. The Company’s evaluation entails analyzing prospective operating budgets and forecasts for expectations of the Company’s cash needs, and comparing those needs to its available cash, cash equivalents and marketable securities. The Company has recurring losses and expects to have recurring losses for the foreseeable future with the continued commercialization of TAZVERIK in ES and FL, the development of tazemetostat in other indications, and the development of the Company’s other product candidates. In addition, the Company has experienced and continues to experience challenges in the commercialization of TAZVERIK resulting from the ongoing COVID-19 pandemic, which the Company believes has had an adverse impact on TAZVERIK revenues. In response to the challenges that the Company has continued to face since the Company commenced its launch of TAZVERIK in FL in June 2020, the Company implemented an operational cost reduction plan in August 2021, implemented further expense reductions in March 2022, and continues to evaluate its costs on an ongoing basis with the intention to streamline such costs. In addition, in connection with its ongoing review of the Company’s strategic plans and financing needs, the Company’s board of directors established a special committee in January 2022 to work with the Company’s management in connection with the exploration and consideration of a possible strategic transaction, a possible equity financing and a possible restructuring or refinancing of the Company’s outstanding indebtedness under the Amended and Restated Loan Agreement. The analysis of the Company’s ability to continue as a going concern for the second quarter of 2022 included consideration of the Company’s current cash needs, including its research and development plans, commercialization activities associated with the continued commercialization of TAZVERIK in the ES and FL indications, its existing debt service obligations, anticipated cost savings resulting from its operational cost reduction plans, including ongoing efforts to eliminate costs not related to the Company’s strategic focus. The analysis included forecasted product revenues from sales of TAZVERIK. Such estimates of future sales contain significant judgment as TAZVERIK was first launched in the first half of 2020 and there is little history with which to base such estimates. In addition, the Company’s ongoing efforts to eliminate costs not related to the Company’s strategic focus contains uncertainties as to whether the Company can attain such benefits. Based on the analysis, the Company concluded that its available cash, cash equivalents and marketable securities as of June 30, 2022 will not be sufficient to fund current planned operations and capital expenditure requirements and pay its debt service obligations as they become due through at least 12 months from the date these financial statements are issued. These conditions raise substantial doubt about the Company’s ability to continue as a going concern for a period of at least one year from the date these financial statements are issued. The Company’s ability to continue to fund its operations is dependent on management’s plans, which include the proposed acquisition by Ipsen described above. The Company’s current operating plan is based on assumptions that may prove to be wrong including that the proposed merger with Ipsen will close, and the Company could use its capital resources sooner than it expects, in which case the Company would evaluate further reductions in its expenses or obtaining additional financing sooner than it otherwise would through equity or debt financing, which additional financing may not be available or may only be available on terms that are not acceptable to the Company. Due to the inherent uncertainties with respect to these actions, management concluded they were not probable of occurrence and therefore do not mitigate the conditions that raise substantial doubt about the Company’s ability to continue as a going concern. The accompanying unaudited condensed consolidated financial statements do not include any adjustments that might be necessary if the Company is not able to continue as a going concern.
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements In August 2020, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2020-06, Debt - Debt with Conversion and Other Options (Subtopic 470-20) and Derivatives and Hedging - Contracts in Entity’s Own Equity (Subtopic 815-40) (“ASU 2020-06”) to simplify accounting for certain financial instruments. ASU 2020-06 eliminates the current models that require separation of beneficial conversion and cash conversion features from convertible instruments and simplifies the derivative scope exception guidance pertaining to equity classification of contracts in an entity’s own equity. The new standard also introduces additional disclosures for convertible debt and freestanding instruments that are indexed to and settled in an entity’s own equity. ASU 2020-06 amends the diluted earnings per share guidance, including the requirement to use the if-converted method for all convertible instruments. The Company adopted ASU 2020-06 effective as of January 1, 2022. The adoption of ASU 2020-06 did not have an impact on the Company’s financial statements.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when a customer obtains control of promised goods or services, in an amount that reflects the consideration which the Company expects to receive in exchange for those goods or services. To determine revenue recognition, the Company performs the following five steps: (i) identify the contract(s) with a customer; (ii) identify the performance obligations in the contract; (iii) determine the transaction price; (iv) allocate the transaction price to the performance obligations in the contract; and (v) recognize revenue when (or as) the Company satisfies a performance obligation. The Company only applies the five-step model to contracts when it is probable that the Company will collect the consideration it is entitled to in exchange for the goods or services it transfers to the customer. For a further discussion of accounting for net product revenue see Note 3, Product Revenue, Net .
Other Revenue	Other Revenue Other revenue consists of revenue from the sales of tazemetostat active pharmaceutical ingredient ("API"), drug product to the Company’s licensees or collaborators and non-cash royalty revenue related to sale of future royalties. The Company recognizes revenue on tazemetostat API and drug product when control has transferred under the terms of each agreement.
Cost of Revenues	Cost of Revenues Cost of revenues primarily consists of costs related to the sales of TAZVERIK and sales of tazemetostat API and drug product to the Company’s licensees or collaborators. These costs include materials, labor, manufacturing overhead, amortization of milestone payments, and royalties payable on net sales of TAZVERIK. Cost of revenues for each of the three and six months ended June 30, 2022 included approximately $ 2.3 million related to sales of tazemetostat drug product. Cost of revenues for the six months ended June 30, 2021 included approximately $ 0.8 million related to sales of tazemetostat drug product. There were no sales of tazemetostat drug product during the three months ended June 30, 2021.
Accounts Receivable	Accounts Receivable The Company extends credit to customers based on its evaluation of the customer’s financial condition. The Company records receivables for all billings when amounts are due under standard terms. Accounts receivable are stated at amounts due net of applicable prompt pay discounts and other contractual adjustments as well as an allowance for doubtful accounts. The Company assesses the need for an allowance for doubtful accounts by considering a number of factors, including the length of time trade accounts receivable are past due, the customer’s ability to pay its obligation and the condition of the general economy and the industry as a whole. The Company will write off accounts receivable when the Company determines that they are uncollectible. In general, the Company has experienced no significant collection issues with its customers.
Inventory	Inventory The Company outsources the manufacturing of TAZVERIK and uses contract manufacturers to produce the raw and intermediate materials used in the production of TAZVERIK as well as the finished product. The Company currently has one supplier qualified for each step in the manufacturing process and is in the process of qualifying additional suppliers. Inventory is composed of raw materials, intermediate materials, which are classified as work-in-process, and finished goods, which are goods that are available for sale. The Company states inventory at the lower of cost or net realizable value with the cost based on the first-in, first-out method. Inventory is classified as long-term when it is expected to be utilized beyond the Company’s normal operating cycle and is included in restricted cash and other assets on the Company's condensed consolidated balance sheets. If the Company identifies excess, obsolete or unsalable items, it writes down its inventory to its net realizable value in the period in which the impairment is identified. These adjustments are recorded based upon various factors related to the product, including the level of product manufactured by the Company, the level of product in the distribution channel, current and projected demand, the expected shelf-life of the product and firm inventory purchase commitments. Shipping and handling costs incurred for inventory purchases are included in inventory costs and costs incurred for product shipments are recorded as incurred in cost of revenue.
Intangible Assets, Net	Intangible Assets, Net Intangible assets consist of capitalized milestone payments made to third parties under an in-license of patent rights upon receiving regulatory approval of TAZVERIK. The finite-lived intangible assets are being amortized on a straight-line basis over the expected time period the Company will benefit from the in-licensed rights, which is generally the patent life. Intangible assets are recorded at cost at the time of their acquisition and are stated in the Company’s condensed consolidated balance sheets net of accumulated amortization and impairments, if applicable. The amortization expense is recognized as cost of revenue in the Company’s condensed consolidated statement of operations and comprehensive loss. During 2020 the Company paid a total of $ 50.0 million in milestone payments under its agreement with Eisai, Co., Ltd. (“Eisai”) following regulatory approval of tazemetostat for ES and FL. These regulatory milestones have been capitalized as intangible assets. The following table presents intangible assets as of June 30, 2022 (in thousands): June 30, 2022 Estimated useful In-licensed rights $ 50,000 12.2 Less: accumulated amortization ( 9,228 ) Total intangible asset, net $ 40,772 The Company recorded approximately $ 1.0 million and $ 2.1 million in amortization expense related to intangible assets, using the straight-line methodology, during each of the three and six months ended June 30, 2022 and 2021, respectively. Estimated future amortization expense for intangible assets for the remainder of the year ended December 31, 2022 is $ 2.1 million and approximately $ 4.2 million per year thereafter. The Company assesses its intangible assets for impairment if indicators are present or changes in circumstance suggest that impairment may exist. Events that could result in an impairment, or trigger an interim impairment assessment, include the receipt of additional clinical or nonclinical data regarding one of the Company’s drug candidates or a potentially competitive drug candidate, changes in the clinical development program for a drug candidate, or new information regarding potential sales for the drug. If impairment indicators are present or changes in circumstance suggest that impairment may exist, the Company performs a recoverability test by comparing the sum of the estimated undiscounted cash flows of each intangible asset to its carrying value on the Company's condensed consolidated balance sheets. If the undiscounted cash flows used in the recoverability test are less than the carrying value, the Company would determine the fair value of the intangible asset and recognize an impairment loss if the carrying value of the intangible asset exceeds its fair value. During the three months ended June 30, 2021, the Company concluded the lower than anticipated current and projected future revenue, due to the impact of the COVID-19 pandemic as well as other factors, was an indicator that impairment may exist related to its finite-lived intangible assets. As a result, the Company performed a recoverability test and determined that the finite-lived intangible assets were recoverable. The Company’s quantitative assessment considered significant assumptions related to estimates of future TAZVERIK sales, offset by direct costs to derive the sales. The estimates of future TAZVERIK sales and associated costs included estimates of significant growth, however, these estimates were uncertain as the product was first launched in the first half of 2020 and due to the uncertainties associated with the ongoing COVID-19 pandemic. Given the limited history of sales and the inherent difficulty in making a long-range forecast, such estimates contained significant uncertainty. If the assumptions regarding forecasted revenue or the costs to derive such revenues made at that time prove to be inaccurate, the Company may be required to perform future impairment analyses and record an impairment charge for its intangible assets in future periods.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2022
Accounting Policies [Abstract]
Summary of Intangible Assets	The following table presents intangible assets as of June 30, 2022 (in thousands): June 30, 2022 Estimated useful In-licensed rights $ 50,000 12.2 Less: accumulated amortization ( 9,228 ) Total intangible asset, net $ 40,772

Product Revenue Net (Tables)

Product Revenue Net (Tables)	6 Months Ended
	Jun. 30, 2022
Net Product Revenue [Member]
Concentration Risk [Line Items]
Schedules of Concentration of Risk Percentage	Revenue earned from each customer as a percentage of net product revenue is as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 Customer 1 37 % 31 % 40 % 36 % Customer 2 9 % 8 % 10 % 11 % Customer 3 14 % 46 % 17 % 37 % Customer 4 24 % 14 % 21 % 16 % Customer 5 16 % 0 % 11 % 0 %
Accounts Receivable [Member]
Concentration Risk [Line Items]
Schedules of Concentration of Risk Percentage	As of June 30, 2022 and December 31, 2021, the five individual customers represented as a percentage of accounts receivable as follows: June 30, December 31, Customer 1 21 % 15 % Customer 2 12 % 10 % Customer 3 16 % 22 % Customer 4 25 % 29 % Customer 5 26 % 24 %
TAZVERIK [Member]
Concentration Risk [Line Items]
Summary of Product Revenue Allowance and Reserve Categories	The following table summarizes activity in each of the above product revenue allowances and reserve categories for the six months ended June 30, 2022: Chargebacks, Government Fees Rebates Returns Total (In thousands) Balance, January 1, 2022 $ 244 $ 586 $ 109 $ 939 Provision 1,139 2,539 22 3,700 Payments or credits ( 1,106 ) ( 2,423 ) — ( 3,529 ) Balance, June 30, 2022 $ 277 $ 702 $ 131 $ 1,110

Cash (Tables)

Cash (Tables)	6 Months Ended
	Jun. 30, 2022
Cash and Cash Equivalents [Abstract]
Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash	A reconciliation of cash, cash equivalents, and restricted cash reported within the Company's condensed consolidated balance sheets that sum to the total of the same such amounts shown in the Company's condensed consolidated statements of cash flows, is as follows: As of June 30, 2022 2021 (In thousands) Cash and cash equivalents $ 71,066 $ 80,164 Restricted cash, as part of other assets 1,509 1,509 Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows $ 72,575 $ 81,673

Marketable Securities (Tables)

Marketable Securities (Tables)	6 Months Ended
	Jun. 30, 2022
Investments, Debt and Equity Securities [Abstract]
Summary of Available-for-Sale Securities Held	The following table summarizes the available-for-sale securities held at June 30, 2022 (in thousands): Description Amortized Unrealized Unrealized Fair Value Commercial paper $ 15,942 $ — $ ( 16 ) $ 15,926 U.S. government agency securities and U.S. Treasuries 57,653 — ( 233 ) 57,420 Total $ 73,595 $ — $ ( 249 ) $ 73,346 The following table summarizes the available-for-sale securities held at December 31, 2021 (in thousands): Description Amortized Unrealized Unrealized Fair Value Commercial paper $ 68,427 $ 7 $ ( 3 ) $ 68,431 U.S. government agency securities and U.S. Treasuries 10,025 — ( 1 ) 10,024 Total $ 78,452 $ 7 $ ( 4 ) $ 78,455

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	6 Months Ended
	Jun. 30, 2022
Fair Value Disclosures [Abstract]
Summary of Company's Financial Assets Recognized at Fair Value	As of June 30, 2022 and December 31, 2021, the Company’s financial assets recognized at fair value consisted of the following: Fair Value as of June 30, 2022 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 61,518 $ 40,355 $ 21,163 $ — Marketable securities: Commercial paper 15,926 — 15,926 — U.S. government agency securities and treasuries 57,420 — 57,420 — Total $ 134,864 $ 40,355 $ 94,509 $ — Fair Value as of December 31, 2021 Total Level 1 Level 2 Level 3 (In thousands) Cash equivalents $ 88,637 $ 67,209 $ 21,428 $ — Marketable securities: Commercial paper 68,431 — 68,431 — U.S. government agency securities and treasuries 10,024 — 10,024 — Total $ 167,092 $ 67,209 $ 99,883 $ —

Inventory (Tables)

Inventory (Tables)	6 Months Ended
	Jun. 30, 2022
Inventory Disclosure [Abstract]
Summary of Inventory	All of the Company’s inventory relates to the manufacturing of TAZVERIK. The following table sets forth the Company’s inventory as of June 30, 2022 and December 31, 2021: June 30, December 31, (In thousands) Raw materials $ 1,676 $ 3,227 Work in process 17,930 13,748 Finished goods 917 1,710 Total $ 20,523 $ 18,685 Balance sheet classification Inventory $ 5,542 $ 3,216 Restricted cash and other assets 14,981 15,469 Total $ 20,523 $ 18,685

Supplemental Balance Sheet In_2

Supplemental Balance Sheet Information (Tables)	6 Months Ended
	Jun. 30, 2022
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Accrued Expenses	Accrued expenses consisted of the following: June 30, December 31, (In thousands) Employee compensation and benefits $ 7,614 $ 11,737 Research and development expenses 10,488 13,744 Current portion of liability related to the sale of future royalties 592 273 Professional services and other 5,977 5,023 Accrued expenses $ 24,671 $ 30,777

Leases (Tables)

Leases (Tables)	6 Months Ended
	Jun. 30, 2022
Leases [Abstract]
Summary of Lease Costs and Company's Operating Leases	The following table contains a summary of the lease costs recognized under ASC 842 and other information pertaining to the Company’s operating leases for the three and six months ended June 30, 2022 and 2021: Three Months Ended Six Months Ended 2022 2021 2022 2021 (in thousands) Lease cost Operating lease cost $ 1,689 $ 1,515 $ 3,378 $ 3,031 Variable lease cost 491 566 933 1,046 Total lease cost $ 2,180 $ 2,081 $ 4,311 $ 4,077 Other information Operating cash flows used for operating leases $ 1,589 $ 1,621 $ 3,216 $ 3,225 Weighted average remaining lease term 3.7 years 4.6 years 3.7 years 4.6 years Weighted average discount rate 9.75 % 9.86 % 9.75 % 9.86 %
Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases	Future minimum lease payments under the Company’s non-cancelable operating leases as of June 30, 2022, are as follows: (In thousands) 2022 $ 3,361 2023 7,517 2024 7,322 2025 3,057 Thereafter 3,909 Total lease payments $ 25,166 Less: imputed interest ( 4,338 ) Total operating lease liabilities at June 30, 2022 $ 20,828

Sale of Future Royalties (Table

Sale of Future Royalties (Tables)	6 Months Ended
	Jun. 30, 2022
Deferred Revenue Disclosure [Abstract]
Schedule of Activity of Royalty Obligation	The following table shows the activity of the Royalty Obligation since the transaction inception through June 30, 2022: As of June 30, 2022 (In thousands) Proceeds from sale of future royalties $ 12,601 Non-cash royalty revenue ( 93 ) Non-cash interest expense recognized 4,104 Liability related to the sale of future royalties - ending balance $ 16,612 Less current portion ( 592 ) Related party liability related to sale of future royalties, net of current portion $ 16,020

Long Term Debt (Tables)

Long Term Debt (Tables)	6 Months Ended
	Jun. 30, 2022
Debt Disclosure [Abstract]
Schedule of Minimum Aggregate Future Loan Payments	The Company has the following minimum aggregate future loan payments at June 30, 2022 : As of June 30, 2022 (In thousands) 2022 $ — 2023 — 2024 70,000 2025 75,000 2026 75,000 Total minimum payments 220,000 Less amounts representing interest and discount ( 3,115 ) Less current portion — Long-term debt, net of current portion $ 216,885

Stockholders' (Deficit) Equity

Stockholders' (Deficit) Equity (Tables)	6 Months Ended
	Jun. 30, 2022
Equity [Abstract]
Summary of Change in Fair Value of Warrant Liability	The following table rolls forward the fair value of the HutchMed Warrant liability, the fair value of which is determined by Level 3 inputs at inception on August 7, 2021, and as of June 30, 2022: (In thousands) Fair value at January 1, 2022 $ 1,930 Decrease in fair value ( 1,350 ) Fair value at June 30, 2022 $ 580
Summary of Key Assumptions Used to Value Warrant	The key assumptions used to value the HutchMed Warrant were as follows: Inception As of June 30, 2022 Risk-free interest rate 0.6 % 2.99 % Expected term (in years) 4.0 years 3.11 years Expected volatility of underlying stock 70.0 % 88.3 % Expected dividend yield — — Stock price $ 6.47 $ 1.47

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	6 Months Ended
	Jun. 30, 2022
Share-based Payment Arrangement [Abstract]
Schedule of Stock-Based Compensation Expense	Stock-based compensation expense is classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended Six Months Ended June 30, 2022 2021 2022 2021 (In thousands) (In thousands) Research and development $ 1,417 $ 2,023 $ 3,209 $ 4,253 General and administrative 3,034 4,695 6,531 9,480 Total $ 4,451 $ 6,718 $ 9,740 $ 13,733
Assumptions Used in Applying Pricing Model	Key assumptions used to apply this pricing model were as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 Risk-free interest rate 2.7 % 0.8 % 2.2 % 0.5 % Expected life of options 5.87 years 5.71 years 5.94 years 5.94 years Expected volatility of underlying stock 74.2 % 70.7 % 73.1 % 70.5 % Expected dividend yield 0.0 % 0.0 % 0.0 % 0.0 %
Summary of Stock Option Activity	The following is a summary of stock option activity for the six months ended June 30, 2022: Number of Weighted Weighted Aggregate (In thousands) (In years) (In thousands) Outstanding at December 31, 2021 12,946 $ 11.61 Granted 5,681 1.29 Exercised — — Forfeited ( 3,204 ) 11.26 Outstanding at June 30, 2022 15,423 $ 7.87 8.06 $ 1,073 Exercisable at June 30, 2022 5,525 $ 13.85 5.95 $ —
Summary of Service Based Restricted Stock Units	During the six months ended June 30, 2022 , 87,500 RSUs were granted to an executive (the “executive RSUs”) and 80,946 RSUs were granted to non-employee directors (the “non-employee RSUs”). RSUs vest based on continuing service to the Company. Assuming all service conditions are achieved, the executive RSUs will vest in three equal installments with the first installment vesting approximately six and a half months following the grant date and the second and third installments vesting annually thereafter, and the non-employee director RSUs will vest as to 100 % of the RSUs on the earlier of the first anniversary of the grant date and the date of the succeeding annual meeting of stockholders. Number Weighted Outstanding at December 31, 2021 2,222 $ 8.70 Granted 169 1.00 Vested ( 361 ) 12.57 Forfeited ( 537 ) 7.62 Outstanding at June 30, 2022 1,493 $ 7.28

Loss Per Share (Tables)

Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2022
Earnings Per Share [Abstract]
Basic and Diluted Loss Per Share	Basic and diluted loss per share allocable to common stockholders are computed as follows: Three Months Ended Six Months Ended 2022 2021 2022 2021 (In thousands except per share data) (In thousands except per share data) Net loss $ ( 35,744 ) $ ( 64,363 ) $ ( 91,249 ) $ ( 134,637 ) Weighted average shares outstanding 166,990 102,053 155,658 101,922 Basic and diluted loss per share allocable to common stockholders $ ( 0.21 ) $ ( 0.63 ) $ ( 0.59 ) $ ( 1.32 )
Common Stock Equivalents Excluded from Calculation of Diluted Loss Per Share Attributable to Common Stockholders	The following common stock equivalents were excluded from the calculation of diluted loss per share allocable to common stockholders because their inclusion would have been anti-dilutive: As of June 30, 2022 2021 (In thousands) Stock options 15,423 12,058 Restricted stock units 1,493 1,358 Shares issuable under employee stock purchase plan 83 113 Series A Preferred Stock (if converted) — 3,378 Warrants 8,153 2,500 25,152 19,407

The Company - Additional Inform

The Company - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			3 Months Ended				6 Months Ended
	Jun. 27, 2022	Aug. 09, 2021	Jun. 30, 2022	Mar. 31, 2022	Sep. 30, 2021	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Basis Of Presentation [Line Items]
Proceeds from issuance of common stock, net of commissions							$ 82,257	$ 1,534
Issuance of common stock, Value				$ 81,828		$ 1,534
Proceeds from sale of redeemable convertible preferred stock							$ 76,000
Initial public offering completion date							May 2013
Cash, cash equivalents, and marketable securities			$ 144,400				$ 144,400
Accumulated deficit			(1,331,084)				(1,331,084)		$ (1,239,835)
Selling, general and administrative			24,111			33,891	51,315	70,303
Research and development			$ 28,054			$ 34,858	57,834	$ 67,561
Ipsen Pharma SAS [Member]
Basis Of Presentation [Line Items]
Stock price	$ 1.45
Contingent payment per share	$ 1
Percentage of share	50%
Termination fee							9,900
RPI Finance Trust (RPI) and BioPharma Credit Investments V (Master) LP and BioPharma Credit PLC (the Lenders) [Member]
Basis Of Presentation [Line Items]
Fund received from collaborators							368,100
RPI Finance Trust [Member]
Basis Of Presentation [Line Items]
Proceeds from issuance of common stock, net of commissions							150,000
Royalty Pharma and Pharmakon Advisors [Member]
Basis Of Presentation [Line Items]
Aggregate fund, amount							1,650,200
Non-equity funding through collaboration agreement							268,800
BioPharma Credit Investments V Master LP And BioPharma Credit PLC [Member]
Basis Of Presentation [Line Items]
Debt financing received through loan agreement							218,100
Operating Cost Reduction Plan [Member]
Basis Of Presentation [Line Items]
Percentage of cross-functional reduction of current workforce		11%		12%
Severance and termination costs		$ 2,000		$ 2,500
Selling, general and administrative				1,700	$ 1,600
Research and development				$ 800	$ 400
IPO [Member]
Basis Of Presentation [Line Items]
Issuance of common stock, Value							$ 937,300

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2022	Dec. 31, 2020
Accounting Policies [Line Items]
Cost of revenue	$ 5,169	$ 2,492	$ 7,808	$ 5,346
Amortization of Intangible Assets	1,000	2,100	1,000	2,100
Estimated future amortization of intangible assets					$ 2,100
Estimated future amortization of intangible assets thereafter					$ 4,200
Tazemetostat Drug Pruducts [Member]
Accounting Policies [Line Items]
Cost of revenue	$ 2,300	$ 0	$ 2,300	$ 800
Eisai [Member]
Accounting Policies [Line Items]
Milestone payments						$ 50,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Summary of Intangible Assets (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Goodwill and Intangible Assets Disclosure [Abstract]
In-licensed rights	$ 50,000
Less: accumulated amortization	(9,228)
Total intangible asset, net	$ 40,772	$ 42,849
Estimated useful life (years)	12 years 2 months 12 days

Product Revenue Net - Summary o

Product Revenue Net - Summary of Product Revenue Allowance and Reserve Categories (Detail) - TAZVERIK [Member] $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	$ 939
Provision	3,700
Payments or credits	(3,529)
Ending Balance	1,110
Chargebacks, Discounts, and Fees [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	244
Provision	1,139
Payments or credits	(1,106)
Ending Balance	277
Government and Other Rebates [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	586
Provision	2,539
Payments or credits	(2,423)
Ending Balance	702
Returns [Member]
Valuation And Qualifying Accounts Disclosure [Line Items]
Beginning Balance	109
Provision	22
Payments or credits	0
Ending Balance	$ 131

Product Revenue Net - Additiona

Product Revenue Net - Additional Information (Detail) - Customer	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Accounts Receivable [Member] | Credit Concentration Risk [Member]
Product Information [Line Items]
Number of customers	4	4	4	4

Product Revenue Net - Schedule

Product Revenue Net - Schedule Of Each Customer As a Percentage Of Net Product Revenue (Detail) - Net Product Revenue [Member] - Customer Concentration Risk [Member]	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Customer 1 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	37%	31%	40%	36%
Customer 2 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	9%	8%	10%	11%
Customer 3 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	14%	46%	17%	37%
Customer 4 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	24%	14%	21%	16%
Customer 5 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	16%	0%	11%	0%

Product Revenue Net - Schedul_2

Product Revenue Net - Schedule Of Each Customer As a Percentage Of Accounts Receivable (Detail) - Accounts Receivable [Member] - Credit Concentration Risk [Member]	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Customer 1 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	21%	15%
Customer 2 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	12%	10%
Customer 3 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	16%	22%
Customer 4 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	25%	29%
Customer 5 [Member]
Concentration Risk [Line Items]
Concentration risk, percentage	26%	24%

Cash - Summary of Reconciliatio

Cash - Summary of Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Cash and Cash Equivalents [Abstract]
Cash and cash equivalents	$ 71,066	$ 98,336	$ 80,164
Restricted cash, as part of other assets	1,509		1,509
Total cash, cash equivalents, and restricted cash shown in the condensed consolidated statements of cash flows	$ 72,575		$ 81,673

Cash - Additional Information (

Cash - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2022	Jun. 30, 2021
Cash And Cash Equivalents [Line Items]
Restricted Cash	$ 1.5	$ 1.5
Security deposit	0.5
Letter of Credit [Member] | Technology Square [Member]
Cash And Cash Equivalents [Line Items]
Security deposit	0.5	0.5
Letter of Credit [Member] | Hampshire Street [Member]
Cash And Cash Equivalents [Line Items]
Security deposit	$ 1	$ 1

Marketable Securities - Summary

Marketable Securities - Summary of Available-for-Sale Securities Held (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Schedule of Available-for-sale Securities [Line Items]
Available-For-Sale Securities Held, Amortized Cost	$ 73,595	$ 78,452
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		7
Available-For-Sale Securities Held, Gross Unrealized Losses	(249)	(4)
Available-For-Sale Securities Held, Fair Value	73,346	78,455
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-For-Sale Securities Held, Amortized Cost	15,942	68,427
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		7
Available-For-Sale Securities Held, Gross Unrealized Losses	(16)	(3)
Available-For-Sale Securities Held, Fair Value	15,926	68,431
U.S. Government Agency Securities and U.S. Treasuries [Member]
Schedule of Available-for-sale Securities [Line Items]
Available-For-Sale Securities Held, Amortized Cost	57,653	10,025
Available-for-sale Securities, Accumulated Gross Unrealized Gain, before Tax		0
Available-For-Sale Securities Held, Gross Unrealized Losses	(233)	(1)
Available-For-Sale Securities Held, Fair Value	$ 57,420	$ 10,024

Marketable Securities - Additio

Marketable Securities - Additional Information (Detail) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($) Security
Schedule of Available-for-sale Securities [Line Items]
Realized gains (losses) recognized on sale or maturity of marketable equity securities	$ 0
Available-for-sale securities, continuous unrealized loss position, less than twelve months, fair value	73,300
Available-for-sale securities, continuous unrealized loss position, 12 months or longer, aggregate loss	$ 300
Weighted average maturity period	3 months
U S Treasury Securities Member
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position | Security	14
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of securities in unrealized loss position | Security	4

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Company's Financial Assets Recognized at Fair Value (Detail) - Fair Value, Measurements, Recurring [Member] - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	$ 61,518	$ 88,637
Total	134,864	167,092
U.S. Government Agency Securities and U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Marketable securities	57,420	10,024
Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Marketable securities	15,926	68,431
Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	40,355	67,209
Total	40,355	67,209
Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Cash equivalents	21,163	21,428
Total	94,509	99,883
Level 2 [Member] | U.S. Government Agency Securities and U.S. Treasuries [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Marketable securities	57,420	10,024
Level 2 [Member] | Commercial Paper [Member]
Fair Value Assets And Liabilities Measured On Recurring Basis [Line Items]
Marketable securities	$ 15,926	$ 68,431

Inventory - Summary of Inventor

Inventory - Summary of Inventory (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Raw materials	$ 1,676	$ 3,227
Work in process	17,930	13,748
Finished goods	917	1,710
Inventory, Noncurrent, Total	20,523	18,685
Inventory
Inventory, Noncurrent, Total	5,542	3,216
Restricted Cash And Other Assets
Inventory, Noncurrent, Total	$ 14,981	$ 15,469

Supplemental Balance Sheet In_3

Supplemental Balance Sheet Information - Schedule of Accrued Expenses (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Accrued Liabilities, Current [Abstract]
Employee compensation and benefits	$ 7,614	$ 11,737
Research and development expenses	10,488	13,744
Current portion of liability related to the sale of future royalties	592	273
Professional services and other	5,977	5,023
Accrued expenses	$ 24,671	$ 30,777

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Income Tax Disclosure [Abstract]
Federal income tax provision or benefit	$ 100,000	$ 0	$ 100,000	$ 0

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail) $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)
Commitments and Contingencies Disclosure [Abstract]
Payments for Merger Related Costs	$ 9.9

Leases - Additional Information

Leases - Additional Information (Detail) - USD ($)			6 Months Ended
	Aug. 11, 2021	Aug. 16, 2019	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021
Lessee Lease Description [Line Items]
Monthly base rent	$ 377,000,000		$ 200,000
Increase in base rent	388,000		33,000
Annual increase of base rent			9,000
Security deposit			500,000
Tenant Allowance	430,000
Operating Lease, Right-of-Use Asset	$ 7,000,000		18,124,000	$ 20,054,000
Hampshire Street [Member] | Letter of Credit [Member]
Lessee Lease Description [Line Items]
Security deposit			$ 1,000,000		$ 1,000,000
Operating lease extend description	the Company extended the term of the Technology Square Lease through November 30, 2024
BMR-Hampshire LLC [Member] | Cambridge [Member]
Lessee Lease Description [Line Items]
Operating lease description		the Company entered into a lease (the "Hampshire Street Lease") with BMR-Hampshire LLC ("BMR"). The Hampshire Street Lease is for 33,525 rentable square feet of office space in Cambridge, Massachusetts. The Hampshire Street Lease commenced as of December 1, 2019
Operating lease extend description		the Company with an option to extend the lease term for one additional five-year period
Operating lease rent expense		$ 200,000
Operating lease rent expense incremental percentage		2.50%

Leases - Summary of Lease Costs

Leases - Summary of Lease Costs and Company's Operating Leases (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Leases [Abstract]
Operating lease cost	$ 1,689	$ 1,515	$ 3,378	$ 3,031
Variable lease cost	491	566	933	1,046
Total lease cost	2,180	2,081	4,311	4,077
Operating cash flows used for operating leases	$ 1,589	$ 1,621	$ 3,216	$ 3,225
Weighted average remaining lease term	3 years 8 months 12 days	4 years 7 months 6 days	3 years 8 months 12 days	4 years 7 months 6 days
Weighted average discount rate	9.75%	9.86%	9.75%	9.86%

Leases - Schedule of Future Min

Leases - Schedule of Future Minimum Lease Payments Under Non-Cancelable Operating Leases (Detail) $ in Thousands	Mar. 31, 2022 USD ($)
Leases [Abstract]
2022	$ 3,361
2023	7,517
2024	7,322
2025	3,057
Thereafter	3,909
Total lease payments	25,166
Less: imputed interest	(4,338)
Total operating lease liabilities at March 31, 2022	$ 20,828

Collaborations and Licensing _2

Collaborations and Licensing Agreements - Additional Information (Details)			3 Months Ended		6 Months Ended
	Aug. 07, 2021 USD ($) $ / shares shares	Jan. 01, 2011 Optiontarget	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Jul. 31, 2019 USD ($)	Mar. 31, 2018 USD ($)
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Regulatory milestone payments obligation									$ 900,000
Reimbursements receivable of regulatory milestone									$ 1,000,000
Roche [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Regulatory milestone payments obligation										$ 1,000,000
Notice period in days					90 days
Research and Development Obligation [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Estimated variable consideration					$ 4,000,000
Manufacturing Material [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue			$ 3,800,000
License Revenue [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Transaction Price			11,800,000
License Revenue [Member] | License, Research and Development Service [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Transaction Price					4,700,000
Transaction price recognized			800
License and Material Right [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Transaction Price			600,000
Transaction price recognized			100,000
HutchMed License Agreement [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Percentage cost incurred for global studies and total number of patients enrolled In the territory	20%
Percentage cost incurred for global studies not specific to any territory	20%
Development and regulatory milestone payment	$ 110,000,000
Royalties payable for licensed product, description	Royalties are payable for each Licensed Product commencing on the first commercial sale of the applicable Licensed Product and ending, on a Jurisdiction-by-Jurisdiction basis, on the latest of expiration of specified patent coverage, expiration of specified regulatory exclusivity or a specified period following the first commercial sale in such Jurisdiction and may be reduced in various circumstances.
Clinical license agreement expiration terms	HutchMed License Agreement will expire upon the expiration of the last royalty term for the last Licensed Product in the Field in the Territory. HutchMed may terminate the HutchMed License Agreement in its entirety for any or no reason upon 12 months’ prior written notice to the Company.
Upfront milestone					13,000,000
Nonrefundable upfront payment received	$ 25,000,000
HutchMed License Agreement [Member] | License, Research and Development Service [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Transaction Price					17,100,000
HutchMed License Agreement [Member] | License Revenue [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Total revenue					12,000,000
HutchMed License Agreement [Member] | License and Material Right [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Revenue remaining performance obligation			12,000,000		12,000,000
HutchMed License Agreement [Member] | Common Stock [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Date prior to which warrants are exercisable	Aug. 07, 2025
Number of securities into which the class of warrant or right may be converted | shares	5,653,000
Exercise price of warrants | $ / shares	$ 11.50
HutchMed License Agreement [Member] | Maximum [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Sales milestone payment	$ 175,000,000
GSK [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Number of option targets | Optiontarget		3
Eisai [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Obligation related to World Wide Royalty			1,300,000	$ 1,200,000	2,600,000	$ 2,100,000
Other Receivables			100,000		100,000		$ 100,000
Royalties payable					1,300,000	1,200,000
Eisai [Member] | Tazemetostat Drug Pruducts [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Deferred revenue								$ 5,000,000
Total revenue				$ 5,000,000		$ 6,300,000
Royalty Pharma and Pharmakon Advisors [Member] | Roche [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Remaining unpaid milestone payments			1,000,000		1,000,000						$ 10,400,000
Reimbursements receivable of development costs			$ 900,000		$ 900,000
Signed Amendment [Member] | Roche [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Regulatory milestone payments obligation										500,000
Fourth Amendment [Member] | Roche [Member]
Revenue Recognition, Multiple-deliverable Arrangements [Line Items]
Regulatory milestone payments obligation										$ 500,000

Sale of Future Royalties - Addi

Sale of Future Royalties - Additional Information (Details)		1 Months Ended			3 Months Ended		6 Months Ended
	Nov. 04, 2019 USD ($) Tranche $ / shares shares	Nov. 30, 2020 USD ($)	Feb. 29, 2020 USD ($) shares	Nov. 30, 2019 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) shares	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($) shares	Jun. 30, 2021 USD ($)	Dec. 31, 2021 shares	Nov. 03, 2020 USD ($)	Jun. 30, 2020 USD ($)
Line Of Credit Facility [Line Items]
Common stock, shares issued | shares					168,365,000		168,365,000		106,098,000
Proceeds from issuance of common stock, net of commissions							$ 82,257,000	$ 1,534,000
Royalty Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Proceeds from sale of future royalties							12,601,000
Non-cash royalty revenue							(93,000)
Non cash interest expense					$ 400,000	$ 500,000	$ 700,000	900,000
RPI and Affiliates [Member]
Line Of Credit Facility [Line Items]
Percentage of ownership interest related parties					18.90%		18.90%		8.60%
Tazemetostat [Member] | Royalty Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Non-cash royalty revenue					$ 40,000	$ 0	$ 66,000	$ 0
RPI Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Common stock, shares issued | shares	6,666,667
Warrants To Exercise Common Stock | $ / shares	$ 20			$ 20
Proceed from agreement	$ 100,000,000
Obligation to purchase common stock	50,000,000
Shares option to sell exercised by underwriters | shares			2,500,000
Proceeds from issuance of common stock, net of commissions			$ 50,000,000
Proceeds from sale of future royalties							$ 12,600,000
Effective annual interest Rate							9.01%
RPI Purchase Agreement [Member] | RPI and Affiliates [Member]
Line Of Credit Facility [Line Items]
Payments for Royalties							9.20%
RPI Purchase Agreement [Member] | Achievement of Specified Annual Net Sales [Member]
Line Of Credit Facility [Line Items]
Potential milestone payments	$ 1,500,000,000
Maximum [Member] | RPI Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Warrants to purchase shares of common stock | shares	2,500,000			2,500,000
Obligation to purchase share price | $ / shares	$ 20
Loan Agreement [Member] | RPI Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Transaction costs					$ 2,000,000		$ 2,000,000
Loan Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity	$ 70,000,000
Percentage of commitment fee paid		2%		2%
Number of tranches | Tranche	3
Aggregate principal amount	$ 70,000,000
Commitment fee		$ 150,000,000		$ 70,000,000
Loan Agreement [Member] | RPI Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Common stock, shares issued | shares					79,000,000		79,000,000
Warrants to purchase shares of common stock | shares							8,400,000
Proceed from agreement							$ 125,000,000
Proceeds from sale of future royalties							12,600,000
Loan Agreement [Member] | Maximum [Member]
Line Of Credit Facility [Line Items]
Right to request for additional loan amount	$ 300,000,000
First Tranche [Member] | Loan Agreement [Member]
Line Of Credit Facility [Line Items]
Aggregate principal amount											$ 25,000,000
First Tranche [Member] | Loan Agreement [Member] | RPI Purchase Agreement [Member]
Line Of Credit Facility [Line Items]
Aggregate principal amount					$ 25,000,000		$ 25,000,000
Second Tranche [Member] | Loan Agreement [Member]
Line Of Credit Facility [Line Items]
Aggregate principal amount											25,000,000
Third Tranche [Member] | Loan Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity											$ 20,000,000
Fourth Tranche [Member] | Amended And Restated Loan Agreement [Member]
Line Of Credit Facility [Line Items]
Line of credit facility, maximum borrowing capacity										$ 150,000,000
Tranche Term Loan [Member]
Line Of Credit Facility [Line Items]
Interest rate of loan										7.75%
Tranche Term Loan [Member] | Interest Rate Floor [Member]
Line Of Credit Facility [Line Items]
Interest rate of loan										2%

Sale of Future Royalties - Sche

Sale of Future Royalties - Schedule of Activity of Royalty Obligation (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Deferred Revenue Arrangement [Line Items]
Related party liability related to sale of future royalties, net of current portion	$ 16,020	$ 15,654
Royalty Purchase Agreement [Member]
Deferred Revenue Arrangement [Line Items]
Proceeds from sale of future royalties	12,601
Non-cash royalty revenue	(93)
Non-cash interest expense recognized	4,104
Related party liability related to sale of future royalties, net of current portion	16,612
Less current portion	(592)
Related party liability related to sale of future royalties, net of current portion	$ 16,020

Long-Term Debt - Additional Inf

Long-Term Debt - Additional Information (Detail)		1 Months Ended		3 Months Ended		6 Months Ended
	Nov. 03, 2020 USD ($) Installment	Nov. 30, 2020 USD ($)	Nov. 30, 2019 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2020 USD ($)	Nov. 04, 2019 USD ($)
Tranche Term Loan [Member]
Debt Instrument [Line Items]
Interest rate of loan	7.75%
Number of quarterly payments of term loan | Installment	8
Description of prepayment of tranche term loan						Each of the four term loans may be prepaid before maturity in whole or in part, however there is a $50.0 million minimum prepayment for any prepayment of the loans. If the Company prepays any tranche of term loans, in whole or in part, during the first 36 months from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to the greater of (x) a make-whole amount equal to the interest that would have accrued on the principal amount to be prepaid and (y) a premium equal to 0.03 multiplied by the principal amount to be prepaid. If the Company prepays a tranche of term loan, in whole or in part, between the 36th month and 48th month from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to 0.02 multiplied by the principal amount to be prepaid. If the Company prepays a tranche of term loans, in whole or in part, between the 48th month and 60th month from the date on which the Lenders funded such tranche of term loans, then the Company must pay a prepayment premium equal to 0.01 multiplied by the principal amount to be prepaid.
Tranche Term Loan [Member] | Interest Rate Floor [Member]
Debt Instrument [Line Items]
Interest rate of loan	2%
First Tranche [Member] | BioPharma Credit Investments V (Master) LP [Member]
Debt Instrument [Line Items]
Interest Expense Credit Facilities				$ 5,400,000	$ 5,400,000	$ 10,800,000	$ 10,800,000
Minimum [Member] | Tranche Term Loan [Member]
Debt Instrument [Line Items]
Prepayment of loan	$ 50,000,000
Loan Agreement [Member]
Debt Instrument [Line Items]
Aggregate principal amount									$ 70,000,000
Percentage of commitment fee paid		2%	2%
Commitment fee		$ 150,000,000	$ 70,000,000
Loan Agreement [Member] | First Tranche [Member]
Debt Instrument [Line Items]
Aggregate principal amount								$ 25,000,000
Loan Agreement [Member] | Maximum [Member]
Debt Instrument [Line Items]
Right to request for additional loan amount									$ 300,000,000
Amended And Restated Loan Agreement [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 150,000,000
Number of quarterly payments of term loan | Installment	4
Debt instrument outstanding interest only payment	$ 70,000,000
Principal And Interest Due	$ 70,000,000
Amended And Restated Loan Agreement [Member] | Tranche Term Loan [Member]
Debt Instrument [Line Items]
Number of quarterly payments of term loan | Installment	8

Long-Term Debt - Schedule of Mi

Long-Term Debt - Schedule of Minimum Aggregate Future Loan Payments (Detail) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Long-term Debt, Fiscal Year Maturity [Abstract]
2022	$ 0
2023	0
2024	70,000
2025	75,000
2026	75,000
Total minimum payments	220,000
Less amounts representing interest and discount	(3,115)
Less current portion	0
Long-term debt, net of current portion	$ 216,885	$ 216,461

Stockholders' (Deficit) Equit_2

Stockholders' (Deficit) Equity - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended					3 Months Ended			6 Months Ended		14 Months Ended
	May 06, 2021	Nov. 04, 2019	May 31, 2022	Jan. 31, 2022	Aug. 31, 2021	Feb. 29, 2020	Nov. 30, 2019	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Mar. 16, 2022	Dec. 31, 2021
Equity [Line Items]
Common stock, shares authorized								450,000,000			450,000,000		450,000,000		225,000,000
Common stock, par value								$ 0.0001			$ 0.0001		$ 0.0001		$ 0.0001
Number of votes for each share of common stock											Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders.
Proceeds from issuance of common stock, net of commissions											$ 82,257	$ 1,534
Additional paid in capital, common stock								$ 48
Issuance of common stock, Value									$ 81,828	$ 1,534
Preferred stock, shares outstanding								0			0		0		338,000
Non cash gains due to adjustment of warrant liability											$ 1,400
Issuance costs											$ 442	$ 105
Maximum [Member]
Equity [Line Items]
Common stock, shares authorized														450,000,000,000
Minimum [Member]
Equity [Line Items]
Common stock, shares authorized														225,000,000
HutchMed Warrants [Member]
Equity [Line Items]
Warrants to purchase shares of common stock					5,653,000
Warrants to exercise common stock					$ 11.50
Number of shares purchasable reduced upon condition					2,826,500
Warrant liability					$ 13,000
RPI Purchase Agreement [Member]
Equity [Line Items]
Proceeds from issuance of common stock, net of commissions						$ 50,000
Warrants to exercise common stock		$ 20					$ 20
RPI Purchase Agreement [Member] | Maximum [Member]
Equity [Line Items]
Warrants to purchase shares of common stock		2,500,000					2,500,000
Series A Convertible Preferred Stock [Member]
Equity [Line Items]
Preferred stock, shares outstanding								0			0		0		337,800
Preferred stock, voting rights											Shares of Series A Preferred Stock will generally have no voting rights except as required by law and except that the consent of the holders of a majority of the outstanding shares of Series A Preferred Stock will be required to amend the terms of the Series A Preferred Stock or take certain other actions with respect to the Series A Preferred Stock.
Liquidation preference per share								$ 0.001			$ 0.001		$ 0.001
Percentage of conversion restriction upon holder of convertible preferred stock shares											9.99%
Conversion of stock notice period											61 days
Number of common shares convertible for each share of convertible preferred stock								10			10		10
Preferred Stock [Member]
Equity [Line Items]
Issuance of Series A Convertible Preferred Stock, net of commissions and beneficial conversion charge, Shares			337,800			12,200
ATM Sale Agreement [Member]
Equity [Line Items]
Common stock shares issued								0			1,473,158		5,314,135
Sale of common stock, price per share								$ 1.82			$ 1.82		$ 1.82
Sale of stock, consideration received on transaction											$ 2,400
Proceeds from issuance of common stock, net of commissions											18,300
Issuance costs											600
IPO [Member]
Equity [Line Items]
Common stock shares issued				56,666,667
Sale of common stock, price per share				$ 1.50
Sale of stock, consideration received on transaction				$ 79,500
Issuance of common stock, Value											$ 937,300
Jefferies LLC [Member] | ATM Sale Agreement [Member]
Equity [Line Items]
Company common stock aggregate offering price	$ 200,000
Commission proceeds from sale	3%
Common Stock [Member]
Equity [Line Items]
Common stock, shares authorized								225,000,000			225,000,000		225,000,000		150,000,000
Issuance of common stock upon exercise of stock options, Share									58,139,825	182,866
Issuance of common stock, Value									$ 6
Issuance of Series A Convertible Preferred Stock, net of commissions and beneficial conversion charge, Shares			3,378,000			122,000		3,378,000
Additional Paid-In Capital [Member]
Equity [Line Items]
Additional paid in capital, common stock								$ 48
Issuance of common stock, Value									$ 81,822	$ 1,534
Additional Paid-In Capital [Member] | RPI Purchase Agreement [Member]
Equity [Line Items]
Proceeds from sale of equity securities fair value							$ 8,400

Stockholders (Deficit) Equity -

Stockholders (Deficit) Equity - Schedule of Fair Value of Warrant Liability (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($)
Equity [Abstract]
Fair value at January 1, 2022	$ 1,930
Decrease in fair value	(1,350)
Fair value at June 30, 2022	$ 580

Stockholders (Deficit) Equity_2

Stockholders (Deficit) Equity - Summary of Key Assumptions Used to Value Warrant (Details) - HutchMed Warrant [Member] - $ / shares		6 Months Ended
	Aug. 07, 2021	Jun. 30, 2022
Equity [Line Items]
Risk-free interest rate	0.60%	2.99%
Expected term (in years)	4 years	3 years 1 month 9 days
Expected volatility of underlying stock	70%	88.30%
Expected dividend yield	0%	0%
Stock price	$ 6.47	$ 1.47

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Apr. 30, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021	May 17, 2022	Apr. 01, 2022
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of stock granted to purchase	800,000
Aggregate common stock shares authorized		450,000,000		450,000,000		225,000,000
Weighted average exercise price of options granted				$ 1.29
Weighted Average Exercise Price per Share, Exercisable		$ 13.85		$ 13.85
Stock-based compensation		$ 4,451	$ 6,718	$ 9,740	$ 13,733
Aggregate stock options granted to employees				5,681,000
Stock-based compensation expense related to stock options, restricted stock, shares issued and shares granted to non-employee directors		4,451	6,718	$ 9,740	$ 13,733
Weighted-average fair value of options granted				$ 0.84	$ 5.10
Unrecognized compensation cost		23,800		$ 23,800
Expected weighted average period for recognition of compensation cost				2 years 8 months 15 days
Unrecognized compensation cost		$ 8,000		$ 8,000
2013 Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate common stock shares authorized							2,500,000
Weighted average exercise price of options granted						$ 5.12
Weighted Average Exercise Price per Share, Exercisable								$ 1.14
Common Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of stock granted to purchase						248,366
Aggregate common stock shares authorized		225,000,000		225,000,000		150,000,000
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate number of stock granted to purchase						106,955
Weighted average grant date fair value, Granted						$ 5.08
Stock-based compensation		$ 4,500	6,700	$ 9,700	$ 13,700
Stock-based compensation expense related to stock options, restricted stock, shares issued and shares granted to non-employee directors		4,500	6,700	$ 9,700	13,700
Service Based RSU [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Weighted average grant date fair value, Granted				$ 1
Expected weighted average period for recognition of compensation cost				1 year 8 months 19 days
Restricted stock units outstanding				169,000
Compensation expense was recognized		$ 1,100	$ 1,200	$ 2,300	$ 2,200
Service Based RSU [Member] | Executives and employees [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units outstanding				87,500
Service Based RSU [Member] | Non-Executive Officer [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted stock units outstanding				80,946
Vesting percentage				100%

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 4,451	$ 6,718	$ 9,740	$ 13,733
Research and Development [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	1,417	2,023	3,209	4,253
General and Administrative [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost [Line Items]
Stock-based compensation	$ 3,034	$ 4,695	$ 6,531	$ 9,480

Stock-Based Compensation - Assu

Stock-Based Compensation - Assumptions Used in Applying Pricing Model (Detail) - Employee Stock Option [Member]	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Risk-free interest rate	2.70%	0.80%	2.20%	0.50%
Expected life of options	5 years 10 months 13 days	5 years 8 months 15 days	5 years 11 months 8 days	5 years 11 months 8 days
Expected volatility of underlying stock	74.20%	70.70%	73.10%	70.50%
Expected dividend yield	0%	0%	0%	0%

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Detail) $ / shares in Units, shares in Thousands, $ in Thousands	6 Months Ended
	Jun. 30, 2022 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Number of Options, Outstanding, Beginning balance | shares	12,946
Number of Options, Granted | shares	5,681
Number of Options, Exercised | shares	0
Number of Options, Forfeited | shares	(3,204)
Number of Options, Outstanding, Ending balance | shares	15,423
Number of Options, Exercisable | shares	5,525
Weighted Average Exercise Price per Share, Outstanding, Beginning balance | $ / shares	$ 11.61
Weighted Average Exercise Price per Share, Granted | $ / shares	1.29
Weighted Average Exercise Price per Share, Exercised | $ / shares	0
Weighted Average Exercise Price per Share, Forfeited | $ / shares	11.26
Weighted Average Exercise Price per Share, Outstanding, Ending balance | $ / shares	7.87
Weighted Average Exercise Price per Share, Exercisable | $ / shares	$ 13.85
Weighted Average Remaining Contractual Term (In Years), Outstanding	8 years 21 days
Weighted Average Remaining Contractual Term (In Years), Exercisable	5 years 11 months 12 days
Aggregate Intrinsic Value, Outstanding | $	$ 1,073
Aggregate Intrinsic Value, Exercisable | $	$ 0

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Service Based Restricted Stock Units (Detail) - Service Based RSU [Member] shares in Thousands	6 Months Ended
	Jun. 30, 2022 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Outstanding Shares, Beginning Balance | shares	2,222
Number of Shares, Granted | shares	169
Number of Shares, Vested | shares	(361)
Number of Shares, Forfeited | shares	(537)
Number of Outstanding Shares, Ending Balance | shares	1,493
Weighted Average Grant Date Fair Value, Beginning Balance | $ / shares	$ 8.70
Weighted Average Grant Date Fair Value, Granted | $ / shares	1
Weighted Average Grant Date Fair Value, Vested | $ / shares	12.57
Weighted Average Grant Date Fair Value, Forfeited | $ / shares	7.62
Weighted Average Grant Date Fair Value, Ending Balance | $ / shares	$ 7.28

Loss Per Share - Schedule of Ba

Loss Per Share - Schedule of Basic and Diluted Loss Per Share (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	3 Months Ended				6 Months Ended
	Jun. 30, 2022	Mar. 31, 2022	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2022	Jun. 30, 2021
Earnings Per Share [Abstract]
Net loss	$ (35,744)	$ (55,505)	$ (64,363)	$ (70,274)	$ (91,249)	$ (134,637)
Weighted average shares outstanding	166,990		102,053		155,658	101,922
Basic and diluted loss per share allocable to common stockholders	$ (0.21)		$ (0.63)		$ (0.59)	$ (1.32)

Loss Per Share - Common Stock E

Loss Per Share - Common Stock Equivalents from Calculation of Diluted Loss Per Share Attributable to Common Stockholders (Detail) - shares shares in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	25,152	19,407
Employee Stock Option [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	15,423	12,058
Restricted Stock Units [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	1,493	1,358
Shares Issuable Under Employee Stock Purchase Plan [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	83	113
Series A Preferred Stock (if converted) [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	0	3,378
Warrants [Member]
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Common stock equivalents excluded from the calculation of diluted loss per share	8,153	2,500