Immunogen (IMGN) 10-Q 1 Aug 22 2022 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2022	Jul. 25, 2022
Document and Entity Information
Document Type	10-Q
Document Quarterly Report	true
Document Transition Report	false
Document Period End Date	Jun. 30, 2022
Entity File Number	0-17999
Entity Registrant Name	ImmunoGen, Inc.
Entity Incorporation, State or Country Code	MA
Entity Tax Identification Number	04-2726691
Entity Address, Address Line One	830 Winter Street
Entity Address, City or Town	Waltham
Entity Address, State or Province	MA
Entity Address, Postal Zip Code	02451
City Area Code	781
Local Phone Number	895-0600
Title of 12(b) Security	Common Stock
Trading Symbol	IMGN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Large Accelerated Filer
Entity Small Business	false
Entity Emerging Growth Company	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		220,713,090
Entity Central Index Key	0000855654
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2022
Document Fiscal Period Focus	Q2
Amendment Flag	false

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
ASSETS
Cash and cash equivalents	$ 373,874	$ 478,750
Accounts receivable	909	4,467
Unbilled receivable	1,874	2,345
Contract assets		3,000
Non-cash royalty receivable	3,168	4,115
Prepaid and other current assets	14,099	7,322
Total current assets	393,924	499,999
Property and equipment, net of accumulated depreciation	4,334	4,663
Operating lease right-of-use assets	11,361	12,392
Other assets	12,676	8,711
Total assets	422,295	525,765
LIABILITIES AND SHAREHOLDERS' EQUITY
Accounts payable	17,245	18,434
Accrued compensation	4,960	5,469
Other accrued liabilities	36,588	23,077
Current portion of liability related to the sale of future royalties, net of deferred financing costs of $187 and $198, respectively	8,772	6,077
Current portion of operating lease liability	3,870	3,537
Current portion of deferred revenue	15,636	44,351
Total current liabilities	87,071	100,945
Deferred revenue, net of current portion	43,611	47,717
Operating lease liability, net of current portion	13,254	15,244
Liability related to the sale of future royalties, net of current portion and deferred financing costs of $282 and $381, respectively	28,062	34,967
Other long-term liabilities	466	1,306
Total liabilities	172,464	200,179
Commitments and contingencies (Note H)
Shareholders' equity:
Preferred stock, $.01 par value; authorized 5,000 shares; no shares issued and outstanding as of each of June 30, 2022 and December 31, 2021
Common stock, $.01 par value; authorized 600,000 shares; 220,644 and 220,361 shares issued and outstanding as of June 30, 2022 and December 31, 2021, respectively	2,206	2,204
Additional paid-in capital	1,804,934	1,794,525
Accumulated deficit	(1,557,309)	(1,471,143)
Total shareholders' equity	249,831	325,586
Total liabilities and shareholders' equity	$ 422,295	$ 525,765

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) shares in Thousands, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
CONSOLIDATED BALANCE SHEETS
Sale of future royalties, current portion and deferred financing costs	$ 187	$ 198
Sale of future royalties, noncurrent portion and deferred financing costs	$ 282	$ 381
Preferred stock, par value (in dollars per share)	$ 0.01	$ 0.01
Preferred stock, authorized shares	5,000	5,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, authorized shares	600,000	600,000
Common stock, issued shares	220,644	220,361
Common stock, outstanding shares	220,644	220,361

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) shares in Thousands, $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenues:
Total revenues	$ 14,162	$ 16,948	$ 52,240	$ 32,654
Operating expenses:
Research and development	51,422	34,589	95,704	69,002
Selling, general and administrative	23,793	9,728	40,441	19,937
Total operating expenses	75,215	44,317	136,145	88,939
Loss from operations	(61,053)	(27,369)	(83,905)	(56,285)
Investment income, net	590	11	644	24
Non-cash interest expense on liability related to the sale of future royalties and convertible senior notes	(1,078)	(3,557)	(2,327)	(8,201)
Interest expense on convertible senior notes		(23)		(47)
Other (expense) income, net	(480)	197	(578)	(283)
Net loss	$ (62,021)	$ (30,741)	$ (86,166)	$ (64,792)
Basic net loss per common share	$ (0.24)	$ (0.15)	$ (0.34)	$ (0.32)
Diluted net loss per common share	$ (0.24)	$ (0.15)	$ (0.34)	$ (0.32)
Basic weighted average common shares outstanding (in shares)	253,336	199,890	253,263	199,365
Diluted weighted average common shares outstanding (in shares)	253,336	199,890	253,263	199,365
Total comprehensive loss	$ (62,021)	$ (30,741)	$ (86,166)	$ (64,792)
License and milestone fees
Revenues:
Total revenues	6,973	252	37,865	409
Non-cash royalty revenue related to the sale of future royalties
Revenues:
Total revenues	7,116	16,690	13,544	32,235
Research and development support
Revenues:
Total revenues	$ 73	$ 6	$ 831	$ 10

CONSOLIDATED STATEMENTS OF SHAR

CONSOLIDATED STATEMENTS OF SHAREHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Total
Balance at Dec. 31, 2020	$ 1,950	$ 1,419,460	$ (1,331,840)	$ 89,570
Balance (in shares) at Dec. 31, 2020	194,998
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(34,051)	(34,051)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 4	1,282		1,286
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	397
Issuance of common stock, net of issuance costs	$ 45	33,447		33,492
Issuance of common stock, net of issuance costs (in shares)	4,544
Restricted stock units vested (in shares)	2
Stock option and restricted stock compensation expense		3,674		3,674
Directors' deferred share unit compensation		149		149
Balance at Mar. 31, 2021	$ 1,999	1,458,012	(1,365,891)	94,120
Balance (in shares) at Mar. 31, 2021	199,941
Balance at Dec. 31, 2020	$ 1,950	1,419,460	(1,331,840)	89,570
Balance (in shares) at Dec. 31, 2020	194,998
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss				(64,792)
Balance at Jun. 30, 2021	$ 2,003	1,463,094	(1,396,632)	68,465
Balance (in shares) at Jun. 30, 2021	200,255
Balance at Mar. 31, 2021	$ 1,999	1,458,012	(1,365,891)	94,120
Balance (in shares) at Mar. 31, 2021	199,941
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(30,741)	(30,741)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	377		378
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	75
Conversion of convertible senior notes	$ 3	997		1,000
Conversion of convertible senior notes (in shares)	239
Common stock issuance costs		(34)		(34)
Stock option and restricted stock compensation expense		3,598		3,598
Directors' deferred share unit compensation		144		144
Balance at Jun. 30, 2021	$ 2,003	1,463,094	(1,396,632)	68,465
Balance (in shares) at Jun. 30, 2021	200,255
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(37,339)	(37,339)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	367		368
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	95
Issuance of common stock, net of issuance costs	$ 21	12,336		12,357
Issuance of common stock, net of issuance costs (in shares)	2,150
Issuance of pre-funded warrants, net of issuance costs		29,765		29,765
Restricted stock award forfeitures	$ (1)	1
Restricted stock award forfeitures (in shares)	(57)
Stock option and restricted stock compensation expense		3,298		3,298
Directors' deferred share unit compensation		179		179
Balance at Sep. 30, 2021	$ 2,024	1,509,040	(1,433,971)	77,093
Balance (in shares) at Sep. 30, 2021	202,443
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(37,172)	(37,172)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 4	1,733		1,737
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	431
Issuance of common stock, net of issuance costs	$ 176	108,039		108,215
Issuance of common stock, net of issuance costs (in shares)	17,487
Issuance of pre-funded warrants, net of issuance costs		169,280		169,280
Stock option and restricted stock compensation expense		6,224		6,224
Directors' deferred share unit compensation		209		209
Balance at Dec. 31, 2021	$ 2,204	1,794,525	(1,471,143)	$ 325,586
Balance (in shares) at Dec. 31, 2021	220,361			220,361
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(24,145)	$ (24,145)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	619		620
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	173
Restricted stock units vested (in shares)	2
Stock option and restricted stock compensation expense		4,196		4,196
Directors' deferred share unit compensation		211		211
Balance at Mar. 31, 2022	$ 2,205	1,799,551	(1,495,288)	306,468
Balance (in shares) at Mar. 31, 2022	220,536
Balance at Dec. 31, 2021	$ 2,204	1,794,525	(1,471,143)	$ 325,586
Balance (in shares) at Dec. 31, 2021	220,361			220,361
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss				$ (86,166)
Balance at Jun. 30, 2022	$ 2,206	1,804,934	(1,557,309)	$ 249,831
Balance (in shares) at Jun. 30, 2022	220,644			220,644
Balance at Mar. 31, 2022	$ 2,205	1,799,551	(1,495,288)	$ 306,468
Balance (in shares) at Mar. 31, 2022	220,536
Increase (Decrease) in Shareholders' Equity (Deficit)
Net loss			(62,021)	(62,021)
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan	$ 1	410		411
Issuance of common stock pursuant to the exercise of stock options and employee stock purchase plan (in shares)	108
Stock option and restricted stock compensation expense		4,760		4,760
Directors' deferred share unit compensation		213		213
Balance at Jun. 30, 2022	$ 2,206	$ 1,804,934	$ (1,557,309)	$ 249,831
Balance (in shares) at Jun. 30, 2022	220,644			220,644

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Cash flows from operating activities:
Net loss	$ (86,166)	$ (64,792)
Adjustments to reconcile net loss to net cash used for operating activities:
Non-cash royalty revenue related to sale of future royalties	(5,590)	(31,721)
Non-cash interest expense on liability related to sale of future royalties and convertible senior notes	2,327	8,201
Depreciation and amortization	931	1,093
Stock and deferred share unit compensation	9,380	7,565
Change in operating assets and liabilities:
Accounts receivable	3,558	28
Unbilled receivable	471	(4,216)
Contract asset	3,000
Prepaid and other current assets	(6,777)	(6,603)
Operating lease right-of-use assets	1,031	866
Other assets	(3,965)	2,100
Accounts payable	(1,249)	2,482
Accrued compensation	(509)	(893)
Other accrued liabilities	12,643	(146)
Deferred revenue	(32,821)	(837)
Operating lease liability	(1,657)	(1,627)
Net cash used for operating activities	(105,393)	(88,500)
Cash flows from investing activities:
Purchases of property and equipment	(514)	(940)
Net cash used for investing activities	(514)	(940)
Cash flows from financing activities:
Proceeds from issuance of common stock under stock plans	1,031	1,664
Proceeds from common stock issuance, net of $106 of transaction costs		33,458
Net cash provided by financing activities	1,031	35,122
Net change in cash and cash equivalents	(104,876)	(54,318)
Cash and cash equivalents, beginning of period	478,750	293,856
Cash and cash equivalents, end of period	$ 373,874	$ 239,538

CONSOLIDATED STATEMENTS OF CA_2

CONSOLIDATED STATEMENTS OF CASH FLOWS (Parenthetical) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Common Stock
Transaction costs	$ 106	$ 106

Nature of Business and Plan of

Nature of Business and Plan of Operations	6 Months Ended
	Jun. 30, 2022
Nature of Business and Plan of Operations
Nature of Business and Plan of Operations	A. Nature of Business and Plan of Operations ​ ImmunoGen, Inc. (the Company) was incorporated in Massachusetts in 1981 and is focused on the development and commercialization of antibody-drug conjugates (ADCs) for the treatment of cancer. The Company has generally incurred operating losses and negative cash flows from operations since inception, incurred a net loss of $86.2 million during the six months ended June 30, 2022, and has an accumulated deficit of approximately $1.6 billion as of June 30, 2022. The Company has primarily funded these losses through payments received from its collaborations and equity, convertible debt, and other financings. To date, the Company has had no revenues from commercial sales of its own products and management expects to continue to incur substantial operating losses for at least the near term as the Company incurs significant operating expenses related to research and development and potential commercialization of its portfolio. As of June 30, 2022, the Company had $373.9 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources will enable it to meet its operational expenses and capital expenditures for more than twelve months after the date these financial statements were issued. The Company expects to raise additional funds through equity, debt, or other financings, or generate revenues from product sales as well as revenues from collaborations through a combination of upfront license payments, milestone payments, royalty payments, and research funding to support its planned operating activities. There can be no assurance, however, that the Company will be able to obtain additional equity, debt, or other financing or generate revenues from product sales or from collaborations on terms acceptable to the Company or at all. The failure of the Company to obtain sufficient funds on acceptable terms when needed could have a material adverse effect on the Company’s business, results of operations, and financial condition and require the Company to defer or limit some or all of its research, development, and/or clinical projects. The Company is subject to risks common to companies in the biotechnology industry including, but not limited to, the development by its competitors of new technological innovations, dependence on key personnel, protection of proprietary technology, manufacturing and marketing limitations, complexities associated with managing collaboration arrangements, third-party reimbursements, and compliance with governmental regulations.

Basis of Presentation and Signi

Basis of Presentation and Significant Accounting Policies	6 Months Ended
	Jun. 30, 2022
Basis of Presentation and Significant Accounting Policies
Basis of Presentation and Significant Accounting Policies	B. Basis of Presentation and Significant Accounting Policies Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated. The consolidated financial statements include all of the adjustments, consisting only of normal recurring adjustments, which management considers necessary for a fair presentation of the Company’s financial position in accordance with accounting principles generally accepted in the U.S. for interim financial information. The December 31, 2021 consolidated balance sheet presented for comparative purposes was derived from the Company’s audited financial statements, and certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. The preparation of interim financial statements requires the use of management’s estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the interim financial statements and the reported amounts of revenues and expenditures during the reported periods. The results of the interim periods are not necessarily indicative of the results for the entire year. Accordingly, the interim financial statements should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 filed with the SEC on February 28, 2022. 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 B to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021. ​ Revenue Recognition Transaction Price Allocated to Future Performance Obligations Deferred revenue under Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC), Revenue from Contracts with Customers 13 61 Contract Balances from Contracts with Customers The following tables present changes in the Company’s contract assets and contract liabilities during the six months ended June 30, 2022 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2021 Additions ​ Deductions ​ Impact of Netting ​ June 30, 2022 Contract asset ​ $ 3,000 ​ $ — ​ $ (3,000) ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 92,068 ​ $ 3,803 ​ $ (36,624) ​ $ — ​ $ 59,247 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2020 ​ Additions ​ Deductions ​ Impact of Netting ​ June 30, 2021 Contract asset ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 110,109 ​ $ — ​ $ (837) ​ $ — ​ $ 109,272 ​ The Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ ​ 2022 ​ 2021 ​ 2022 ​ 2021 Revenue recognized in the period from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amounts included in contract liabilities at the beginning of the period ​ $ 10,864 ​ $ 765 ​ $ 36,624 ​ $ 837 ​ Pursuant to the Company’s license agreement with Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. (Huadong), upon delivery of clinical materials in the six months ended June 30, 2022, the Company recognized as license and milestone fee revenue the remaining $28.5 million of the deferred revenue balance as of December 31, 2021 related to the $45.0 million of upfront and development milestone payments previously received. Additionally, pursuant to a license agreement executed with Eli Lilly and Company (Lilly), during the six months ended June 30, 2022, the Company received an upfront payment of $13.0 million, of which $9.2 million was recognized as license and milestone fee revenue and the remainder deferred, further details of which can be found in Note C, “Agreements.” The Company also recognized $8.0 million of previously deferred non-cash royalty revenue related to the sale of rights to KADCYLA ® During the six months ended June 30, 2021, the Company recognized $0.2 million as license and milestone fee revenue for delivery of certain materials to Viridian Therapeutics that had been previously deferred and recognized $0.1 million of license and milestone fee revenue related to numerous collaborators’ rights to technological improvements that had been previously deferred. Additionally, the Company recorded $0.5 million of previously deferred non-cash royalty revenue related to the sale of rights to KADCYLA royalties. The timing of revenue recognition, billings, and cash collections results in billed receivables, unbilled receivables, contract assets, and contract liabilities on the consolidated balance sheets. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded (under the caption deferred revenue). Contract liabilities are recognized as revenue after control of the products or services is transferred to the customer and all revenue recognition criteria have been met. Financial Instruments and Concentration of Credit Risk Cash and cash equivalents are primarily maintained with three financial institutions in the U.S. Deposits with banks may exceed the amount of insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s cash equivalents consist of money market funds with underlying investments primarily being U.S. Government-issued securities and high quality, short-term commercial paper. Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, and marketable securities. The Company held no marketable securities as of June 30, 2022 and December 31, 2021. The Company’s investment policy, approved by the Board of Directors, limits the amount it may invest in any one type of investment, thereby reducing credit risk concentrations. Cash and Cash Equivalents The Company considers all highly liquid financial instruments with maturities of three months or less when purchased to be cash equivalents. As of June 30, 2022 and December 31, 2021, the Company held $373.9 million and $478.8 million, respectively, in cash and money market funds, which were classified as cash and cash equivalents. Non-cash Investing and Financing Activities The Company had $0.3 million and $0.2 million of accrued capital expenditures as of June 30, 2022 and December 31, 2021, respectively, which have been treated as a non-cash investing activity and, accordingly, are not reflected in the consolidated statement of cash flows. Fair Value of Financial Instruments Fair value is defined under ASC 820, Fair Value Measurements and Disclosures ● Level 1 - Quoted prices in active markets for identical assets or liabilities. ● Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. As of June 30, 2022 and December 31, 2021, the Company held certain assets that are required to be measured at fair value on a recurring basis. The fair value of the Company’s cash equivalents is based on quoted prices from active markets (Level 1 inputs). The carrying amounts reflected in the consolidated balance sheets for accounts receivable, unbilled receivables, prepaid and other current assets, accounts payable, accrued compensation, and other accrued liabilities approximate fair value due to their short-term nature. As of June 30, 2021, the Company had outstanding convertible 4.5% senior notes (convertible notes) with a gross carrying amount and estimated fair value of $1.1 million and $2.3 million, respectively. The fair value of the convertible notes was influenced by interest rates, the Company’s stock price and stock price volatility, and by prices observed in trading activity for the convertible notes. Because there were no trades involving the convertible notes since September 2019, however, the fair value as of June 30, 2021 used Level 3 inputs. In June 2021, $1.0 million of outstanding convertible 4.5% senior notes converted into 238,777 shares of the Company’s common stock, par value $0.01 per share (common stock), with the remaining $1.1 million of convertible 4.5% senior notes paid in cash upon maturity on July 1, 2021. Common Stock Warrants The Company accounts for common stock warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance included in ASC 480, Distinguishing Liabilities from Equity Derivatives and Hedging For issued or modified warrants that meet all of the criteria for equity classification, the warrants are required to be recorded as a component of additional paid-in capital at the time of issuance. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance and remeasured each balance sheet date thereafter. Changes in the estimated fair value of the liability-classified warrants are recognized as a non-cash gain or loss in the accompanying consolidated statements of operations and comprehensive loss. Computation of Net Loss per Common Share Basic and diluted net loss per share is calculated based upon the weighted average number of shares of common stock outstanding during the period. Shares of the Company’s common stock underlying pre-funded warrants are included in the calculation of basic and diluted earnings per share. During periods of income, participating securities are allocated a proportional share of income determined by dividing total weighted-average participating securities by the sum of the total weighted average common shares and participating securities (the two-class method). Shares of the Company’s restricted stock participate in any dividends that may be declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, no loss is allocated to participating securities since they have no contractual obligation to share in the losses of the Company. Diluted loss per share is computed after giving consideration to the dilutive effect of stock options, convertible notes, and restricted stock that are outstanding during the period, except where such non-participating securities would be anti-dilutive. The Company’s common stock equivalents, as calculated in accordance with the treasury-stock method for options and unvested restricted stock, and the if-converted method for the convertible notes, are shown in the following table (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2022 2021 2022 2021 Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock/units at end of period ​ 29,528 ​ 21,681 ​ 29,528 ​ 21,681 Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock/units ​ 958 2,772 ​ 1,306 ​ 3,138 ​ The Company’s common stock equivalents have not been included in the net loss per share calculation because their effect is anti-dilutive due to the Company’s net loss position. Stock-Based Compensation As of June 30, 2022, the Company was authorized to grant future awards under three employee share-based compensation plans, which are the ImmunoGen, Inc. Amended and Restated 2018 Employee, Director and Consultant Equity Incentive Plan (the 2018 Plan), the Employee Stock Purchase Plan (the ESPP), and the ImmunoGen Inducement Equity Incentive Plan (the Inducement Plan). At the annual meeting of shareholders on June 15, 2022, the 2018 Plan was amended to provide for the issuance of stock grants, the grant of options, and the grant of stock-based awards for up to an additional 13,000,000 shares of the Company’s common stock, as well as up to 28,742,013 shares of common stock, which represent the number of shares of common stock remaining under the 2018 Plan as of April 1, 2022, and awards previously granted under the 2018 Plan and the Company’s former stock-based plans, including the ImmunoGen, Inc. 2016 and 2006 Employee, Director and Consultant Equity Incentive Plans, that forfeit, expire, or cancel without delivery of shares of common stock or which resulted in the forfeiture of shares of common stock back to the Company subsequent to April 1, 2022. The Inducement Plan was approved by the Board of Directors in December 2019, and pursuant to subsequent amendments, provides for the issuance of non-qualified option grants for up to 10,500,000 shares of the Company’s common stock. Options awarded under the two plans are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Options vest at various periods of up to four years and may be exercised within ten years of the date of grant under each of these plans. The stock-based awards are accounted for under ASC 718, Compensation—Stock Compensation ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, ​ Six Months Ended June 30, ​ 2022 ​ 2021 ​ 2022 ​ 2021 Dividend ​ None ​ None ​ None ​ None Volatility ​ 83.4% ​ 84.7% ​ 83.1% ​ 85.3% Risk-free interest rate ​ 3.00% ​ 1.01% ​ 2.180% ​ 0.67% Expected life (years) ​ 6.0 ​ 6.0 ​ 6.0 ​ 6.0 ​ Using the Black-Scholes option-pricing model, the weighted-average grant date fair values of options granted during the three months ended June 30, 2022 and 2021 were $3.12 and $4.92 per share, respectively, and $3.57 and $5.40 for options granted during the six months ended June 30, 2022 and 2021, respectively. A summary of option activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ Number ​ Average ​ ​ of Stock ​ Exercise ​ ​ Options ​ Price Outstanding at December 31, 2021 ​ 21,219 ​ $ 6.28 Granted ​ 8,670 ​ ​ 5.03 Exercised ​ (173) ​ ​ 3.59 Forfeited/Canceled ​ (263) ​ ​ 6.72 Outstanding at June 30, 2022 ​ 29,453 ​ $ 5.92 ​ In 2020, the Company issued 2.6 million performance-based stock options to certain employees that will vest upon the achievement of specified performance goals. Upon assessment of the performance-based stock option awards as of December 31, 2021, the Company determined the first performance goal to be probable of vesting and, as such, recorded $2.6 million of stock-based compensation expense for the year ended December 31, 2021. In May 2022, the first performance goal was achieved, resulting in the vesting of 25% of the 2.6 million performance-based stock options. The fair value of the remaining unvested performance-based stock options that could be expensed in future periods is $7.8 million. A summary of restricted stock unit activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted- ​ ​ Restricted ​ Average Grant ​ ​ Stock Shares ​ Date Fair Value Unvested at December 31, 2021 ​ 77 ​ $ 5.59 Granted ​ - ​ ​ - Vested (2) ​ ​ 2.53 Unvested at June 30, 2022 ​ 75 ​ $ 5.68 ​ In June 2018, the Company's Board of Directors, with shareholder approval, adopted the Employee Stock Purchase Plan (ESPP). Following the automatic share increase on January 1, 2021, pursuant to the ESPP’s “evergreen” provision, an aggregate of 2,000,000 shares of common stock have been reserved for issuance under the ESPP. ESPP purchase periods are six months and begin on January 1 and July 1 of each year, with purchase dates occurring on the final business day of the given purchase period. The fair value of each ESPP award is estimated on the first day of the offering period using the Black-Scholes option-pricing model. The Company recognizes share-based compensation expense equal to the fair value of the ESPP awards on a straight-line basis over the offering period. Stock compensation expense related to stock options and restricted stock unit awards granted under the stock plans and the ESPP was $4.8 million and $9.0 million during the three and six months ended June 30, 2022, respectively, compared to stock compensation expense of $3.6 million and $7.3 million for the three and six months ended June 30, 2021, respectively. As of June 30, 2022, the estimated fair value of unvested employee awards, exclusive of performance awards, was $50.1 million. The weighted-average remaining vesting period for these awards is approximately three years. Segment Information During all periods presented, the Company continued to operate in one reportable business segment under the management approach of ASC 280, Segment Reporting During the three months ended June 30, 2022, Roche and Huadong each represented 50% of Recently Adopted Accounting Pronouncements There were no recently issued or effective FASB Accounting Standards Updates (ASUs) that had, or are expected to have, a material effect on the Company's results of operations, financial condition, or liquidity.

Agreements

Agreements	6 Months Ended
	Jun. 30, 2022
Agreements
Agreements	C. Agreements Significant Collaborative Agreements Lilly In February 2022, the Company entered into a license agreement with Eli Lilly and Company (Lilly), pursuant to which the Company granted Lilly worldwide exclusive rights to research, develop, and commercialize antibody-drug conjugates based on the Company’s novel camptothecin technology. Under the terms of the license agreement, the Company received a non-refundable upfront payment of $13.0 million, reflecting initial targets selected by Lilly. Lilly may select a pre-specified number of additional targets, with the Company eligible to receive an additional $32.5 million in exercise fees if Lilly licenses the full number of additional targets over the four year period following the effective date of the license agreement, with the potential for up to $1.7 billion in development and sales-based milestone payments if all targets are selected and all milestones are realized. In addition, the Company is entitled to receive tiered royalties, on a product-by-product basis, as a percentage of worldwide annual net sales by Lilly, based on certain net sales thresholds. Lilly is responsible for all costs associated with the research, development, and commercialization of any ensuing products. The Company evaluated the agreement and determined it was within the scope of ASC 606. The Company determined the promised goods and services included an exclusive license to use the Company’s intellectual property and know-how to research, develop, and commercialize products related to each of the initial targets selected by Lilly. Each of these licenses is distinct, as Lilly can derive benefit from each license independent of any other initial target licenses. Accordingly, the license to each of the initial targets selected by Lilly represents a separate performance obligation. Lilly has the right to replace each of the initial licensed targets once during a specified term for no additional consideration. If Lilly fails to advance an initial or replacement target to a specified stage within a specified period from the date the target was selected, Lilly’s rights to the respective target will cease and will revert back to the Company. The Company determined Lilly’s right to a replacement target for each of the initial targets represented a material right. Each material right is therefore a separate performance obligation. Lilly’s right to select additional targets does not represent a material right as the target fee for each additional target is the same and is also consistent with the target fee for each of the initial targets selected by Lilly. Accordingly, each additional target selected by Lilly, if any, will be accounted for as a separate arrangement. The transaction price was determined to consist of the upfront payment of $13.0 million. Future development milestones have been fully constrained. 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 Lilly. The transaction price of $13.0 million was allocated to the performance obligations based on their relative stand-alone selling prices. In consideration of each target being at the same stage of development at the time of the initial license or at the time of replacement and each target having approximately the same earnings potential, Upon completion of the transfer of intellectual property and know-how to Lilly during the six months ended June 30, 2022, the Company recognized $9.2 million of license and milestone fee revenue related to the portion of the transaction price allocated to the initial target licenses. The $3.8 million allocated to the material rights to obtain licenses to replacement targets is included in long-term deferred revenue as of June 30, 2022 and will be recognized when the right is either exercised or expires. Roche In 2000, the Company granted Genentech, now a unit of Roche, an exclusive development and commercialization license to use the Company’s maytansinoid ADC technology. Pursuant to this agreement, Roche developed and received marketing approval for its HER2-targeting ADC, KADCYLA, in the U.S., Japan, the European Union, and numerous other countries. In accordance with the Company’s revenue recognition policy, $13.5 million and $32.2 million of non-cash royalties on net sales of KADCYLA were recognized and included in non-cash royalty revenue for the six months ended June 30, 2022 and 2021, respectively. The Company sold its rights to receive royalty payments on the net sales of KADCYLA through two separate transactions in 2015 and 2019. Following the 2019 transaction, OMERS, the defined benefit pension plan for municipal employees in the Province of Ontario, Canada, is entitled to receive all of these royalties. Huadong In October 2020, the Company entered into a collaboration and license agreement with Huadong. The collaboration and license agreement grants Huadong an exclusive, royalty-bearing, and sublicensable right to develop and commercialize mirvetuximab soravtansine (the Licensed Product) in the People’s Republic of China, Hong Kong, Macau, and Taiwan (collectively, Greater China). The Company retains exclusive rights to the Licensed Product outside of Greater China. Under the terms of the collaboration and license agreement, the Company received a non-refundable upfront payment of $40.0 million with the potential for approximately $265.0 million in development, regulatory, and sales-based milestone payments. In December 2021, the Company received a $5.0 million payment upon achievement of a development milestone. The Company determined that revenue related to the agreement would be recognized as the clinical supply of the Licensed Product is delivered to Huadong, estimated to be completed over approximately two years . Accordingly, based on clinical supply delivered to Huadong during the six months ended June 30, 2022, the Company recorded the remaining $28.5 million of the deferred revenue balance as of December 31, 2021 related to the $45.0 million of upfront and development milestone payments previously received. Viridian In October 2020, the Company entered into a license agreement with Viridian Therapeutics, Inc. pursuant to which the Company granted Viridian the exclusive right to develop and commercialize an insulin-like growth factor-1 receptor (IGF-1R) antibody for all non-oncology indications that do not use radiopharmaceuticals in exchange for an upfront payment, with the potential to receive up to a total of $143.0 million in development, regulatory, and sales-based milestone payments plus royalties on the commercial sales of any resulting product. In the three months ended December 31, 2021, a $3.0 million development milestone became probable of being achieved, which was allocated to the previously delivered license and recognized as revenue as a component of license and milestone fees for the three months ended December 31, 2021. The development milestone was subsequently achieved in April 2022. For additional information related to these agreements, as well as the Company’s other significant collaborative agreements, please read Note C, “Agreements - Significant Collaborative Agreements,” to the audited financial statements included within the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 filed with the SEC on February 28, 2022.

Liability Related to Sale of Fu

Liability Related to Sale of Future Royalties	6 Months Ended
	Jun. 30, 2022
Liability Related to Sale of Future Royalties
Liability Related to Sale of Future Royalties	D. Liability Related to Sale of Future Royalties In 2015, Immunity Royalty Holdings, L.P. (IRH) purchased the right to receive 100% of the royalty payments on commercial sales of KADCYLA arising under the Company’s development and commercialization license with Genentech, until IRH had received aggregate royalties equal to $235.0 million or $260.0 million, depending on when the aggregate royalties received by IRH reach a specified milestone. Once the applicable threshold was met, the Company would thereafter have received 85% and IRH would have received 15% of the KADCYLA royalties for the remaining royalty term. At the consummation of the transaction, the Company received cash proceeds of $200 million. As part of this sale, the Company incurred $5.9 million of transaction costs, which are presented net of the liability in the accompanying consolidated balance sheet and are being amortized to interest expense over the estimated life of the royalty purchase agreement. Although the Company sold its rights to receive royalties from the sales of KADCYLA, as a result of its then ongoing involvement in the cash flows related to these royalties, the Company continues to account for these royalties as revenue and recorded the $200.0 million in proceeds from this transaction as a liability related to sale of future royalties (Royalty Obligation) that is being amortized using the interest method over the estimated life of the royalty purchase agreement. In January 2019, the Company sold its residual rights to receive royalty payments on commercial sales of KADCYLA to OMERS for a payment of $65.2 million (amount is net of $1.5 million in broker fees). Simultaneously, OMERS purchased IRH’s right to the royalties the Company previously sold to IRH as described above, therefore obtaining the rights to 100% of the royalties received from that date on. Because the Company will not be involved with the cash flows related to the residual royalties, the $65.2 million of net proceeds received from the sale of its residual rights to receive royalty payments was recorded as deferred revenue and will be amortized as the royalty revenue related to the residual rights is earned using the units of revenue approach. During the second quarter of 2021, the aggregate royalty threshold was met and, in accordance with the Company’s revenue recognition policy, $8.0 million and $0.5 million of revenue related to the residual rights was recognized and is included in non-cash royalty revenue for the six months ended June 30, 2022 and 2021, respectively. Additionally, the purchase of IRH’s interest by OMERS did not result in an extinguishment or modification of the original instrument and, accordingly, the Company continues to account for the remaining obligation as a liability as outlined above. The following table shows the activity within the liability account during the six-month period ended June 30, 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended ​ June 30, 2022 Liability related to sale of future royalties, net — beginning balance ​ $ 41,044 Proceeds from sale of future royalties, net ​ — KADCYLA royalty payments received and paid ​ (6,537) Non-cash interest expense recognized ​ ​ 2,327 Liability related to sale of future royalties, net — ending balance ​ $ 36,834 ​ The Company receives royalty reports and royalty payments related to sales of KADCYLA from Roche one

Income Taxes

Income Taxes	6 Months Ended
	Jun. 30, 2022
Income Taxes
Income Taxes	E. Income Taxes ​

Capital Stock

Capital Stock	6 Months Ended
	Jun. 30, 2022
Capital Stock
Capital Stock	F. Capital Stock Pre-Funded Warrants On August 11, 2021, the Company entered into a Securities Purchase Agreement (SPA) with RA Capital Healthcare Fund, L.P. (RA Capital), pursuant to which the Company agreed to sell to RA Capital a pre-funded warrant to purchase up to an aggregate of 5,434,782 shares of the Company’s common stock for $5.51 per share of common stock underlying the pre-funded warrant. The per share exercise price of the pre-funded warrant is $0.01. The private placement resulted in aggregate net proceeds of $29.7 million. In connection with a public offering in December 2021, the Company issued pre-funded warrants to purchase up to an aggregate of 16,000,000 and 11,363,636 shares of the Company’s common stock to RA Capital and Redmile Group, LLC, respectively, for $6.59 per share of common stock underlying the pre-funded warrants, which, together with the per share exercise price of $0.01, is equal to $6.60, the public offering price of the shares of common stock in the public offering, which resulted in aggregate net proceeds of $169.3 million. RA Capital and Redmile Group, LLC are each considered related parties pursuant to ASC 850, Related Party Disclosures The pre-funded warrants’ fundamental transaction provision does not provide the warrant holders with the option to settle any unexercised warrants for cash in the event of any fundamental transactions; rather, in all fundamental transaction scenarios, the warrant holder will only be entitled to receive from the Company or any successor entity the same type or form of consideration (and in the same proportion) that is being offered and paid to the shareholders of the Company in connection with the fundamental transaction, whether that consideration be in the form of cash, stock or any combination thereof. The pre-funded warrants also include a separate provision whereby the exercisability of the warrants may be limited if, upon exercise, the warrant holder or any of its affiliates would beneficially own more than 9.99% of the Company’s common stock. This threshold is subject to the holder’s rights under the pre-funded warrants to increase or decrease such percentage to any other percentage not in excess of 19.99% upon at least 61 days’ prior notice from the holder to the Company. The Company assessed the pre-funded warrants for appropriate equity or liability classification pursuant to the Company’s accounting policy described in Note B, “Summary of Significant Accounting Policies.” During this assessment, the Company determined the pre-funded warrants are freestanding instruments that do not meet the definition of a liability pursuant to ASC 480 and do not meet the definition of a derivative pursuant to ASC 815. The pre-funded warrants are indexed to the Company’s common stock and meet all other conditions for equity classification under ASC 480 and ASC 815. Based on the results of this assessment, the Company concluded that the pre-funded warrants are freestanding equity-linked financial instruments that meet the criteria for equity classification under ASC 480 and ASC 815. Accordingly, the pre-funded warrants were classified as equity and accounted for as a component of additional paid-in capital at the time of issuance and at each subsequent balance sheet date. The Company also determined that the pre-funded warrants should be included in the determination of basic and diluted earnings per share in accordance with ASC 260, Earnings per Share Compensation Policy for Non-Employee Directors Pursuant to the Compensation Policy for Non-Employee Directors, as amended, non-employee directors are granted deferred share units upon initial election to the Board of Directors and annually thereafter. Initial awards and annual retainers vest quarterly over approximately three years and one year from the date of grant, respectively, contingent upon the individual remaining a director of ImmunoGen as of each vesting date. The number of deferred share units awarded is fixed per the policy on the date of the award. All unvested deferred share units will automatically vest immediately prior to the occurrence of a change of control. The redemption amount of deferred share units issued will be paid in shares of common stock of the Company on the date a director ceases to be a member of the Board of Directors. Pursuant to the Compensation Policy for Non-Employee Directors, as amended, non-employee directors also receive stock option awards upon initial election to the Board of Directors and annually thereafter. The directors received a total of approximately 322,000 and 352,000 options in 2022 and 2021, respectively, and the related compensation expense for the three and six months ended June 30, 2022 and 2021 is included in the amounts discussed in the “Stock-Based Compensation” section of Note B above.

Leases

Leases	6 Months Ended
	Jun. 30, 2022
Leases
Leases	G. Leases The Company currently has one In June 2022, in order to reclaim laboratory and office space, the Company modified one of its sublease agreements to terminate the sublease early, targeting an end date of March 31, 2023. Pursuant to the amended sublease agreement, the Company is required to pay the sublessee $3.5 million as a lease incentive, of which $1.8 million was paid in June 2022 and the remainder will be paid at the end of the sublease term. No other terms from the original sublease agreement were modified. In accordance with ASC 842, Leases

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2022
Commitments and Contingencies
Commitments and Contingencies	H. Commitments and Contingencies Research Collaboration Agreement In June 2022, the Company entered into a research collaboration agreement with Oxford BioTherapeutics Ltd (OBT) to develop novel ADCs utilizing the Company’s linker-payload technology directed to targets identified via OBT's proprietary OGAP® discovery platform. Under the terms of the agreement, OBT received a non-refundable $7.5 million upfront payment reflecting OBT's preclinical programs to be included in the collaboration. Additionally, over the initial three-year term of the agreement, the Company is committed to reimbursing OBT up to $2.8 million annually to support research activities dependent on the number of active programs. Otherwise, each party is responsible for its own costs associated with the joint research plan. After antibodies generated by OBT have been conjugated with the Company's proprietary linker-payload technology, each party will have the opportunity to select one or more development programs to further develop on its own. Each party will be eligible to receive milestone payments based on the achievement of pre-specified development and regulatory milestones, as well as tiered royalties as a percentage of worldwide commercial sales, with respect to each program selected by the other party. Once a party has selected a given program, it will be solely responsible for all research and development costs associated with that specific program. If at the end of the initial three-year term, either party elects not to extend the research term, predetermined opt-out fees may apply based on the number of programs selected for further development by each party. At any time starting twelve months after the effective date of the agreement, the Company may terminate the agreement in its sole discretion upon 90 days written notice to OBT. Otherwise, the agreement may be terminated by either party for a material breach by the other party, subject to notice and cure provisions. In accordance with ASC 730, Research and Development Manufacturing Commitments As of June 30, 2022, the Company had noncancelable obligations under several agreements related to in-process and future manufacturing of antibody, drug substance, and cytotoxic agents required for supply of the Company’s product candidates totaling $13.0 million. Additionally, pursuant to commercial agreements for future production of antibody, our noncancelable commitments total $45.1 million at June 30, 2022. Litigation ​ The Company is not a party to any material litigation.

Related Party Transactions

Related Party Transactions	6 Months Ended
	Jun. 30, 2022
Related Party Transactions [Abstract]
Related Party Transactions	I. Related Party Transactions Related Party Disclosures

Subsequent Events

Subsequent Events	6 Months Ended
	Jun. 30, 2022
Subsequent Events
Subsequent Events	J. Subsequent Events The Company has evaluated all events or transactions that occurred after June 30, 2022, up through the date the Company issued these financial statements. The Company did not have any material subsequent events.

Basis of Presentation and Sig_2

Basis of Presentation and Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2022
Basis of Presentation and Significant Accounting Policies
Basis of Presentation	Basis of Presentation The consolidated financial statements include the accounts of the Company and its wholly owned subsidiaries. All intercompany transactions and balances have been eliminated. The consolidated financial statements include all of the adjustments, consisting only of normal recurring adjustments, which management considers necessary for a fair presentation of the Company’s financial position in accordance with accounting principles generally accepted in the U.S. for interim financial information. The December 31, 2021 consolidated balance sheet presented for comparative purposes was derived from the Company’s audited financial statements, and certain information and footnote disclosures normally included in the Company’s annual financial statements have been condensed or omitted. The preparation of interim financial statements requires the use of management’s estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities at the date of the interim financial statements and the reported amounts of revenues and expenditures during the reported periods. The results of the interim periods are not necessarily indicative of the results for the entire year. Accordingly, the interim financial statements should be read in conjunction with the audited financial statements and notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021 filed with the SEC on February 28, 2022.
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 B to the consolidated financial statements included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2021.
Revenue Recognition	Revenue Recognition Transaction Price Allocated to Future Performance Obligations Deferred revenue under Financial Accounting Standards Board (FASB) Accounting Standards Codification (ASC), Revenue from Contracts with Customers 13 61 Contract Balances from Contracts with Customers The following tables present changes in the Company’s contract assets and contract liabilities during the six months ended June 30, 2022 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2021 Additions ​ Deductions ​ Impact of Netting ​ June 30, 2022 Contract asset ​ $ 3,000 ​ $ — ​ $ (3,000) ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 92,068 ​ $ 3,803 ​ $ (36,624) ​ $ — ​ $ 59,247 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2020 ​ Additions ​ Deductions ​ Impact of Netting ​ June 30, 2021 Contract asset ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 110,109 ​ $ — ​ $ (837) ​ $ — ​ $ 109,272 ​ The Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ ​ 2022 ​ 2021 ​ 2022 ​ 2021 Revenue recognized in the period from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amounts included in contract liabilities at the beginning of the period ​ $ 10,864 ​ $ 765 ​ $ 36,624 ​ $ 837 ​ Pursuant to the Company’s license agreement with Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd. (Huadong), upon delivery of clinical materials in the six months ended June 30, 2022, the Company recognized as license and milestone fee revenue the remaining $28.5 million of the deferred revenue balance as of December 31, 2021 related to the $45.0 million of upfront and development milestone payments previously received. Additionally, pursuant to a license agreement executed with Eli Lilly and Company (Lilly), during the six months ended June 30, 2022, the Company received an upfront payment of $13.0 million, of which $9.2 million was recognized as license and milestone fee revenue and the remainder deferred, further details of which can be found in Note C, “Agreements.” The Company also recognized $8.0 million of previously deferred non-cash royalty revenue related to the sale of rights to KADCYLA ® During the six months ended June 30, 2021, the Company recognized $0.2 million as license and milestone fee revenue for delivery of certain materials to Viridian Therapeutics that had been previously deferred and recognized $0.1 million of license and milestone fee revenue related to numerous collaborators’ rights to technological improvements that had been previously deferred. Additionally, the Company recorded $0.5 million of previously deferred non-cash royalty revenue related to the sale of rights to KADCYLA royalties. The timing of revenue recognition, billings, and cash collections results in billed receivables, unbilled receivables, contract assets, and contract liabilities on the consolidated balance sheets. When consideration is received, or such consideration is unconditionally due, from a customer prior to transferring goods or services to the customer under the terms of a contract, a contract liability is recorded (under the caption deferred revenue). Contract liabilities are recognized as revenue after control of the products or services is transferred to the customer and all revenue recognition criteria have been met.
Financial Instruments and Concentration of Credit Risk	Financial Instruments and Concentration of Credit Risk Cash and cash equivalents are primarily maintained with three financial institutions in the U.S. Deposits with banks may exceed the amount of insurance provided on such deposits. Generally, these deposits may be redeemed upon demand and, therefore, bear minimal risk. The Company’s cash equivalents consist of money market funds with underlying investments primarily being U.S. Government-issued securities and high quality, short-term commercial paper. Financial instruments that potentially subject the Company to concentrations of credit risk consist principally of cash, cash equivalents, and marketable securities. The Company held no marketable securities as of June 30, 2022 and December 31, 2021. The Company’s investment policy, approved by the Board of Directors, limits the amount it may invest in any one type of investment, thereby reducing credit risk concentrations.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid financial instruments with maturities of three months or less when purchased to be cash equivalents. As of June 30, 2022 and December 31, 2021, the Company held $373.9 million and $478.8 million, respectively, in cash and money market funds, which were classified as cash and cash equivalents.
Non-cash Investing and Financing Activities	Non-cash Investing and Financing Activities The Company had $0.3 million and $0.2 million of accrued capital expenditures as of June 30, 2022 and December 31, 2021, respectively, which have been treated as a non-cash investing activity and, accordingly, are not reflected in the consolidated statement of cash flows.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Fair value is defined under ASC 820, Fair Value Measurements and Disclosures ● Level 1 - Quoted prices in active markets for identical assets or liabilities. ● Level 2 - Inputs other than Level 1 that are observable, either directly or indirectly, such as quoted prices for similar assets or liabilities; quoted prices in markets that are not active; or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. ● Level 3 – Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. As of June 30, 2022 and December 31, 2021, the Company held certain assets that are required to be measured at fair value on a recurring basis. The fair value of the Company’s cash equivalents is based on quoted prices from active markets (Level 1 inputs). The carrying amounts reflected in the consolidated balance sheets for accounts receivable, unbilled receivables, prepaid and other current assets, accounts payable, accrued compensation, and other accrued liabilities approximate fair value due to their short-term nature. As of June 30, 2021, the Company had outstanding convertible 4.5% senior notes (convertible notes) with a gross carrying amount and estimated fair value of $1.1 million and $2.3 million, respectively. The fair value of the convertible notes was influenced by interest rates, the Company’s stock price and stock price volatility, and by prices observed in trading activity for the convertible notes. Because there were no trades involving the convertible notes since September 2019, however, the fair value as of June 30, 2021 used Level 3 inputs. In June 2021, $1.0 million of outstanding convertible 4.5% senior notes converted into 238,777 shares of the Company’s common stock, par value $0.01 per share (common stock), with the remaining $1.1 million of convertible 4.5% senior notes paid in cash upon maturity on July 1, 2021.
Common Stock Warrants	The Company accounts for common stock warrants as either equity-classified or liability-classified instruments based on an assessment of the warrant’s specific terms and applicable authoritative guidance included in ASC 480, Distinguishing Liabilities from Equity Derivatives and Hedging For issued or modified warrants that meet all of the criteria for equity classification, the warrants are required to be recorded as a component of additional paid-in capital at the time of issuance. For issued or modified warrants that do not meet all the criteria for equity classification, the warrants are required to be recorded at their initial fair value on the date of issuance and remeasured each balance sheet date thereafter. Changes in the estimated fair value of the liability-classified warrants are recognized as a non-cash gain or loss in the accompanying consolidated statements of operations and comprehensive loss.
Computation of Net Loss per Common Share	Computation of Net Loss per Common Share Basic and diluted net loss per share is calculated based upon the weighted average number of shares of common stock outstanding during the period. Shares of the Company’s common stock underlying pre-funded warrants are included in the calculation of basic and diluted earnings per share. During periods of income, participating securities are allocated a proportional share of income determined by dividing total weighted-average participating securities by the sum of the total weighted average common shares and participating securities (the two-class method). Shares of the Company’s restricted stock participate in any dividends that may be declared by the Company and are therefore considered to be participating securities. Participating securities have the effect of diluting both basic and diluted earnings per share during periods of income. During periods of loss, no loss is allocated to participating securities since they have no contractual obligation to share in the losses of the Company. Diluted loss per share is computed after giving consideration to the dilutive effect of stock options, convertible notes, and restricted stock that are outstanding during the period, except where such non-participating securities would be anti-dilutive. The Company’s common stock equivalents, as calculated in accordance with the treasury-stock method for options and unvested restricted stock, and the if-converted method for the convertible notes, are shown in the following table (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2022 2021 2022 2021 Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock/units at end of period ​ 29,528 ​ 21,681 ​ 29,528 ​ 21,681 Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock/units ​ 958 2,772 ​ 1,306 ​ 3,138 ​ The Company’s common stock equivalents have not been included in the net loss per share calculation because their effect is anti-dilutive due to the Company’s net loss position.
Stock-Based Compensation	Stock-Based Compensation As of June 30, 2022, the Company was authorized to grant future awards under three employee share-based compensation plans, which are the ImmunoGen, Inc. Amended and Restated 2018 Employee, Director and Consultant Equity Incentive Plan (the 2018 Plan), the Employee Stock Purchase Plan (the ESPP), and the ImmunoGen Inducement Equity Incentive Plan (the Inducement Plan). At the annual meeting of shareholders on June 15, 2022, the 2018 Plan was amended to provide for the issuance of stock grants, the grant of options, and the grant of stock-based awards for up to an additional 13,000,000 shares of the Company’s common stock, as well as up to 28,742,013 shares of common stock, which represent the number of shares of common stock remaining under the 2018 Plan as of April 1, 2022, and awards previously granted under the 2018 Plan and the Company’s former stock-based plans, including the ImmunoGen, Inc. 2016 and 2006 Employee, Director and Consultant Equity Incentive Plans, that forfeit, expire, or cancel without delivery of shares of common stock or which resulted in the forfeiture of shares of common stock back to the Company subsequent to April 1, 2022. The Inducement Plan was approved by the Board of Directors in December 2019, and pursuant to subsequent amendments, provides for the issuance of non-qualified option grants for up to 10,500,000 shares of the Company’s common stock. Options awarded under the two plans are granted with an exercise price equal to the market price of the Company’s stock at the date of grant. Options vest at various periods of up to four years and may be exercised within ten years of the date of grant under each of these plans. The stock-based awards are accounted for under ASC 718, Compensation—Stock Compensation ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, ​ Six Months Ended June 30, ​ 2022 ​ 2021 ​ 2022 ​ 2021 Dividend ​ None ​ None ​ None ​ None Volatility ​ 83.4% ​ 84.7% ​ 83.1% ​ 85.3% Risk-free interest rate ​ 3.00% ​ 1.01% ​ 2.180% ​ 0.67% Expected life (years) ​ 6.0 ​ 6.0 ​ 6.0 ​ 6.0 ​ Using the Black-Scholes option-pricing model, the weighted-average grant date fair values of options granted during the three months ended June 30, 2022 and 2021 were $3.12 and $4.92 per share, respectively, and $3.57 and $5.40 for options granted during the six months ended June 30, 2022 and 2021, respectively. A summary of option activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ Number ​ Average ​ ​ of Stock ​ Exercise ​ ​ Options ​ Price Outstanding at December 31, 2021 ​ 21,219 ​ $ 6.28 Granted ​ 8,670 ​ ​ 5.03 Exercised ​ (173) ​ ​ 3.59 Forfeited/Canceled ​ (263) ​ ​ 6.72 Outstanding at June 30, 2022 ​ 29,453 ​ $ 5.92 ​ In 2020, the Company issued 2.6 million performance-based stock options to certain employees that will vest upon the achievement of specified performance goals. Upon assessment of the performance-based stock option awards as of December 31, 2021, the Company determined the first performance goal to be probable of vesting and, as such, recorded $2.6 million of stock-based compensation expense for the year ended December 31, 2021. In May 2022, the first performance goal was achieved, resulting in the vesting of 25% of the 2.6 million performance-based stock options. The fair value of the remaining unvested performance-based stock options that could be expensed in future periods is $7.8 million. A summary of restricted stock unit activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted- ​ ​ Restricted ​ Average Grant ​ ​ Stock Shares ​ Date Fair Value Unvested at December 31, 2021 ​ 77 ​ $ 5.59 Granted ​ - ​ ​ - Vested (2) ​ ​ 2.53 Unvested at June 30, 2022 ​ 75 ​ $ 5.68 ​ In June 2018, the Company's Board of Directors, with shareholder approval, adopted the Employee Stock Purchase Plan (ESPP). Following the automatic share increase on January 1, 2021, pursuant to the ESPP’s “evergreen” provision, an aggregate of 2,000,000 shares of common stock have been reserved for issuance under the ESPP. ESPP purchase periods are six months and begin on January 1 and July 1 of each year, with purchase dates occurring on the final business day of the given purchase period. The fair value of each ESPP award is estimated on the first day of the offering period using the Black-Scholes option-pricing model. The Company recognizes share-based compensation expense equal to the fair value of the ESPP awards on a straight-line basis over the offering period. Stock compensation expense related to stock options and restricted stock unit awards granted under the stock plans and the ESPP was $4.8 million and $9.0 million during the three and six months ended June 30, 2022, respectively, compared to stock compensation expense of $3.6 million and $7.3 million for the three and six months ended June 30, 2021, respectively. As of June 30, 2022, the estimated fair value of unvested employee awards, exclusive of performance awards, was $50.1 million. The weighted-average remaining vesting period for these awards is approximately three years.
Segment Information	Segment Information During all periods presented, the Company continued to operate in one reportable business segment under the management approach of ASC 280, Segment Reporting During the three months ended June 30, 2022, Roche and Huadong each represented 50% of
Recently Adopted Accounting Pronouncements	Recently Adopted Accounting Pronouncements There were no recently issued or effective FASB Accounting Standards Updates (ASUs) that had, or are expected to have, a material effect on the Company's results of operations, financial condition, or liquidity.

Basis of Presentation and Sig_3

Basis of Presentation and Significant Accounting Policies (Tables)	6 Months Ended
	Jun. 30, 2022
Basis of Presentation and Significant Accounting Policies
Contract assets and contract liabilities	The following tables present changes in the Company’s contract assets and contract liabilities during the six months ended June 30, 2022 and 2021 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2021 Additions ​ Deductions ​ Impact of Netting ​ June 30, 2022 Contract asset ​ $ 3,000 ​ $ — ​ $ (3,000) ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 92,068 ​ $ 3,803 ​ $ (36,624) ​ $ — ​ $ 59,247 ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Balance at ​ ​ December 31, 2020 ​ Additions ​ Deductions ​ Impact of Netting ​ June 30, 2021 Contract asset ​ $ — ​ $ — ​ $ — ​ $ — ​ $ — Contract liabilities (deferred revenue) ​ $ 110,109 ​ $ — ​ $ (837) ​ $ — ​ $ 109,272 ​ The Company recognized the following revenues as a result of changes in contract asset and contract liability balances in the respective periods (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ ​ 2022 ​ 2021 ​ 2022 ​ 2021 Revenue recognized in the period from: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Amounts included in contract liabilities at the beginning of the period ​ $ 10,864 ​ $ 765 ​ $ 36,624 ​ $ 837
Schedule of common stock equivalents, as calculated in accordance with the treasury-stock method	The Company’s common stock equivalents, as calculated in accordance with the treasury-stock method for options and unvested restricted stock, and the if-converted method for the convertible notes, are shown in the following table (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended ​ Six Months Ended ​ ​ June 30, ​ June 30, ​ 2022 2021 2022 2021 Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock/units at end of period ​ 29,528 ​ 21,681 ​ 29,528 ​ 21,681 Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock/units ​ 958 2,772 ​ 1,306 ​ 3,138
Schedule of risk-free rate of the stock options based on US Treasury rate	​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Three Months Ended June 30, ​ Six Months Ended June 30, ​ 2022 ​ 2021 ​ 2022 ​ 2021 Dividend ​ None ​ None ​ None ​ None Volatility ​ 83.4% ​ 84.7% ​ 83.1% ​ 85.3% Risk-free interest rate ​ 3.00% ​ 1.01% ​ 2.180% ​ 0.67% Expected life (years) ​ 6.0 ​ 6.0 ​ 6.0 ​ 6.0
Summary of stock option activity	A summary of option activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Weighted- ​ ​ Number ​ Average ​ ​ of Stock ​ Exercise ​ ​ Options ​ Price Outstanding at December 31, 2021 ​ 21,219 ​ $ 6.28 Granted ​ 8,670 ​ ​ 5.03 Exercised ​ (173) ​ ​ 3.59 Forfeited/Canceled ​ (263) ​ ​ 6.72 Outstanding at June 30, 2022 ​ 29,453 ​ $ 5.92
Summary of restricted stock activity	A summary of restricted stock unit activity under the Company’s equity plans for the six months ended June 30, 2022 is presented below (in thousands, except weighted-average data): ​ ​ ​ ​ ​ ​ ​ ​ Number of ​ Weighted- ​ ​ Restricted ​ Average Grant ​ ​ Stock Shares ​ Date Fair Value Unvested at December 31, 2021 ​ 77 ​ $ 5.59 Granted ​ - ​ ​ - Vested (2) ​ ​ 2.53 Unvested at June 30, 2022 ​ 75 ​ $ 5.68

Liability Related to Sale of _2

Liability Related to Sale of Future Royalties (Tables)	6 Months Ended
	Jun. 30, 2022
Liability Related to Sale of Future Royalties
Schedule of Liability account during the period from the inception of the royalty transaction	The following table shows the activity within the liability account during the six-month period ended June 30, 2022 (in thousands): ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Six Months Ended ​ June 30, 2022 Liability related to sale of future royalties, net — beginning balance ​ $ 41,044 Proceeds from sale of future royalties, net ​ — KADCYLA royalty payments received and paid ​ (6,537) Non-cash interest expense recognized ​ ​ 2,327 Liability related to sale of future royalties, net — ending balance ​ $ 36,834

Nature of Business and Plan o_2

Nature of Business and Plan of Operations (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Net loss			$ (86,166)	$ (64,792)
Accumulated deficit	$ (1,557,309)		(1,557,309)		$ (1,471,143)
Total revenues	14,162	$ 16,948	52,240	$ 32,654
Cash and cash equivalents	$ 373,874		$ 373,874		$ 478,750
Number of months Capital resources meets capital expenditures			12 months
Product
Total revenues			$ 0

Basis of Presentation and Sig_4

Basis of Presentation and Significant Accounting Policies - Performance Obligations (Details) $ in Millions	Jun. 30, 2022 USD ($)
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Revenue, Remaining Performance Obligation	$ 59.2
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, percent	0.26%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, percent	0.62%
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2032-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligations, percent	0.12%
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2023-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	12 months
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	13 months
Minimum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2032-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	61 months
Maximum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2027-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	60 months
Maximum | Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2032-07-01
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction [Line Items]
Remaining performance obligation, expected timing of satisfaction	120 months

Basis of Presentation and Sig_5

Basis of Presentation and Significant Accounting Policies - Contract Balances (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Changes in the Company's contract assets and contract liabilities
Contract asset, Beginning balance	$ 3,000
Contract asset, Additions		$ 0
Contract asset, Deductions	3,000
Contract liabilities:
Contract liabilities (deferred revenue), Beginning balance	92,068	110,109
Contract liabilities (deferred revenue), Additions	3,803
Contract liabilities (deferred revenue), Deductions	(36,624)	(837)
Contract liabilities (deferred revenue), Ending balance	$ 59,247	$ 109,272

Basis of Presentation and Sig_6

Basis of Presentation and Significant Accounting Policies - Revenues Recognized as a Result of Changes in Contract Asset and Liability Balances (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Revenue recognized in the period from:
Amounts included in contract liabilities at the beginning of the period	$ 10,864	$ 765	$ 36,624	$ 837

Basis of Presentation and Sig_7

Basis of Presentation and Significant Accounting Policies - Contract Balances from Contracts with Customers - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Feb. 28, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue	$ 59,247	$ 109,272	$ 59,247	$ 109,272		$ 92,068	$ 110,109
Revenue from contract with customer	14,162	16,948	52,240	32,654
Revenue recognized, previously deferred	10,864	765	36,624	837
License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer	6,973	$ 252	37,865	409
Hangzhou Zhongmei Huadong Pharmaceutical Co., Ltd | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue						28,500
License agreement upfront payment receivable						$ 45,000
Lilly
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
License agreement upfront payment receivable					$ 13,000
Lilly | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer			9,200
Lilly | Upfront payment
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Deferred revenue	$ 13,000		13,000
KADCYLA
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net proceeds from sale of residual rights to receive royalty payments				500
KADCYLA | Royalty revenue
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Net proceeds from sale of residual rights to receive royalty payments			8,000
Viridian | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue from contract with customer			$ 200
Revenue recognized, previously deferred				200
CytomX and Novartis | License and milestone fees
Revenue, Initial Application Period Cumulative Effect Transition [Line Items]
Revenue recognized, previously deferred				$ 100

Basis of Presentation and Sig_8

Basis of Presentation and Significant Accounting Policies - Financial Instruments and Concentration of Credit Risk (Details)	6 Months Ended
	Jun. 30, 2022 USD ($) item	Dec. 31, 2021 USD ($)
Financial Instruments and Concentration of Credit Risk
Number of financial institutions in the U.S. in which cash and cash equivalents are primarily maintained | item	3
Marketable securities held by entity | $	$ 0	$ 0

Basis of Presentation and Sig_9

Basis of Presentation and Significant Accounting Policies - Cash and Cash Equivalents (Details) - USD ($) $ in Thousands	Jun. 30, 2022	Dec. 31, 2021
Basis of Presentation and Significant Accounting Policies
Cash and cash equivalents	$ 373,874	$ 478,750

Basis of Presentation and Si_10

Basis of Presentation and Significant Accounting Policies - Non-cash Investing and Financing Activities (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2022	Dec. 31, 2021
Basis of Presentation and Significant Accounting Policies
Accrued capital expenditures	$ 0.3	$ 0.2

Basis of Presentation and Si_11

Basis of Presentation and Significant Accounting Policies - Fair Value of Financial Instruments (Details) $ / shares in Units, $ in Thousands		3 Months Ended	6 Months Ended
	Jul. 01, 2021 USD ($)	Jun. 30, 2021 USD ($) $ / shares	Jun. 30, 2021 USD ($) item $ / shares shares	Jun. 30, 2022 $ / shares	Dec. 31, 2021 $ / shares
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt amount		$ 1,000
Number of trades | item			0
Common stock, par value (in dollars per share) | $ / shares		$ 0.01	$ 0.01	$ 0.01	$ 0.01
Convertible 4.5% Senior Notes
Fair value hierarchy for the Company's financial assets measured at fair value
Interest rate (as a percent)	4.50%	4.50%	4.50%
Gross carrying amount		$ 1,100	$ 1,100
Convertible debt amount			$ 1,000
Convertible debt, number of common shares issued | shares			238,777
Convertible debt paid in cash	$ 1,100
Significant Other Observable Inputs (Level 2) | Convertible 4.5% Senior Notes | Estimated fair value
Fair value hierarchy for the Company's financial assets measured at fair value
Convertible debt fair value		$ 2,300	$ 2,300

Basis of Presentation and Si_12

Basis of Presentation and Significant Accounting Policies - Computation of Net Loss per Common Share (Details) - shares shares in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Computation of Net Loss per Common Share
Options outstanding to purchase common stock, shares issuable under the employee stock purchase plan, and unvested restricted stock/units at end of period	29,528	21,681	29,528	21,681
Common stock equivalents under treasury stock method for options, shares issuable under the employee stock purchase plan, and unvested restricted stock/units	958	2,772	1,306	3,138

Basis of Presentation and Si_13

Basis of Presentation and Significant Accounting Policies - Stock-Based Compensation (Details) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	May 31, 2022 shares	Jun. 30, 2022 USD ($) $ / shares shares	Jun. 30, 2021 USD ($) $ / shares	Jun. 30, 2022 USD ($) plan $ / shares shares	Jun. 30, 2021 USD ($) $ / shares	Dec. 31, 2021 USD ($) $ / shares shares	Dec. 31, 2020 shares	Jun. 15, 2022 shares	Apr. 01, 2022 shares	Jun. 30, 2018 shares
Stock-Based Compensation
Number of employee share-based compensation plans | plan				3
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)		0%	0%	0%	0%
ESPP
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Aggregate number of common shares reserved for future issuance										2,000,000
Stock options and restricted stock awards
Stock-Based Compensation
Vesting period				3 years
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Stock compensation expense | $		$ 4.8	$ 3.6	$ 9	$ 7.3
Estimated fair value that could be expensed | $		$ 50.1		$ 50.1
Stock options
Weighted-average assumptions used to estimate the fair value of each stock option
Dividend (as a percent)		0%	0%	0%	0%
Volatility (as a percent)		83.40%	84.70%	83.10%	85.30%
Risk-free interest rate (as a percent)		3%	1.01%	2.18%	0.67%
Expected life		6 years	6 years	6 years	6 years
Weighted-average grant date fair value (in dollars per share) | $ / shares		$ 3.12	$ 4.92	$ 3.57	$ 5.40
Number of Stock Options
Outstanding at the beginning of the period (in shares)				21,219,000
Granted (in shares)				8,670,000
Exercised (in shares)				(173,000)
Forfeited/Canceled (in shares)				(263,000)
Outstanding at the end of the period (in shares)		29,453,000		29,453,000		21,219,000
Weighted-Average Exercise Price
Outstanding at the beginning of the period (in dollars per share) | $ / shares				$ 6.28
Granted (in dollars per share) | $ / shares				5.03
Exercised (in dollars per share) | $ / shares				3.59
Forfeited/Canceled (in dollars per share) | $ / shares				6.72
Outstanding at the end of the period (in dollars per share) | $ / shares		$ 5.92		$ 5.92		$ 6.28
Performance shares
Stock-Based Compensation
Vesting percentage	25%
Number of Stock Options
Granted (in shares)	2,600,000						2,600,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Additional Disclosures [Abstract]
Stock compensation expense | $						$ 2.6
Estimated fair value that could be expensed | $		$ 7.8		$ 7.8
Restricted stock
Number of Restricted Stock Shares
Unvested at the beginning of the period (in shares)				77,000
Vested (in shares)				(2,000)
Unvested at the end of the period (in shares)		75,000		75,000		77,000
Weighted-Average Grant Date Fair Value
Unvested at the beginning of the period (in dollars per share) | $ / shares				$ 5.59
Vested (in dollars per share) | $ / shares				2.53
Unvested at the end of the period (in dollars per share) | $ / shares		$ 5.68		$ 5.68		$ 5.59
Immunogen Inc Restated Stock Option Plan
Stock-Based Compensation
Common stock authorized for issuance (in shares)									28,742,013
2018 Plan
Stock-Based Compensation
Common stock authorized for issuance (in shares)								13,000,000
Inducement Plan
Stock-Based Compensation
Number of employee share-based compensation plans | plan				2
Common stock authorized for issuance (in shares)		10,500,000		10,500,000
2018 Plan and Inducement Plan
Stock-Based Compensation
Exercise period				10 years
2018 Plan and Inducement Plan | Maximum
Stock-Based Compensation
Vesting period				4 years

Basis of Presentation and Si_14

Basis of Presentation and Significant Accounting Policies - Segment Information (Details) - segment	3 Months Ended		6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021
Segment Information
Number of operating segments			1
Other customers | Revenue | Customer concentration
Segment Information
Percentages of revenue recognized	0%	0%	0%	0%
Roche | Revenue | Customer concentration
Segment Information
Percentages of revenue recognized	50%	99%	26%
Roche | Revenue | Customer concentration
Segment Information
Percentages of revenue recognized				99%
Huadong | Revenue | Customer concentration
Segment Information
Percentages of revenue recognized	50%		56%
Lilly | Revenue | Customer concentration
Segment Information
Percentages of revenue recognized			17%

Agreements - Lilly (Details)

Agreements - Lilly (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Feb. 28, 2022	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Collaborative Agreements disclosures
Aggregate amount of transaction price allocated to remaining performance obligations		$ 59,200		$ 59,200
Revenue from contract with customer		14,162	$ 16,948	52,240	$ 32,654
Amount of obligation included in long-term deferred revenue		43,611		43,611		$ 47,717
Lilly
Collaborative Agreements disclosures
License agreement upfront payment receivable	$ 13,000
License agreement additional payment receivable	$ 32,500
License agreement additional target term	4 years
License agreement, target selection fees and development, regulatory and commercial milestone payments receivable	$ 1,700,000
Aggregate amount of transaction price allocated to remaining performance obligations	13,000
Lilly | Upfront payment
Collaborative Agreements disclosures
Estimated payments to received	13,000
Lilly | Initial targets
Collaborative Agreements disclosures
Revenue from contract with customer	9,200			9,200
Lilly | Material rights to obtain licenses to replacement targets
Collaborative Agreements disclosures
Revenue from contract with customer	$ 3,800
Amount of obligation included in long-term deferred revenue		$ 3,800		$ 3,800

Agreements - Roche (Details)

Agreements - Roche (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2022	Jun. 30, 2021
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties	$ 5,590	$ 31,721
Roche | KADCYLA
Collaborative Agreements disclosures
Non-cash royalty revenue related to sale of future royalties	$ 13,500	$ 32,200

Agreements - Huadong (Details)

Agreements - Huadong (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		6 Months Ended		12 Months Ended
	Oct. 31, 2020	Jun. 30, 2022	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2021
Collaborative Agreements disclosures
Revenue from contract with customer		$ 14,162	$ 16,948	$ 52,240	$ 32,654
Revenue recognized, previously deferred		10,864	765	36,624	837
Upfront payment | Huadong
Collaborative Agreements disclosures
Revenue from contract with customer	$ 40,000
Upfront payment | Huadong | Development milestones
Collaborative Agreements disclosures
Revenue recognized, previously deferred				28,500		$ 45,000
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer		$ 6,973	$ 252	$ 37,865	$ 409
License and milestone fees | Huadong | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer						$ 5,000
License and milestone fees | Huadong | Sales milestones
Collaborative Agreements disclosures
Potential milestone payment	$ 265,000
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2024-07-01 | License and milestone fees | Huadong | Development milestones
Collaborative Agreements disclosures
Remaining performance obligation, expected timing of satisfaction		2 years		2 years

Agreements - Viridian (Details)

Agreements - Viridian (Details) - USD ($) $ in Thousands	3 Months Ended			6 Months Ended
	Jun. 30, 2022	Dec. 31, 2021	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Oct. 31, 2020
Collaborative Agreements disclosures
Revenue from contract with customer	$ 14,162		$ 16,948	$ 52,240	$ 32,654
License and milestone fees
Collaborative Agreements disclosures
Revenue from contract with customer	$ 6,973		$ 252	37,865	$ 409
Viridian | License and milestone fees
Collaborative Agreements disclosures
Potential milestone payment						$ 143,000
Revenue from contract with customer				$ 200
Viridian | License and milestone fees | Development milestones
Collaborative Agreements disclosures
Revenue from contract with customer		$ 3,000

Liability Related to Sale of _3

Liability Related to Sale of Future Royalties (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended	6 Months Ended		12 Months Ended
	Jan. 31, 2019	Jun. 30, 2021	Jun. 30, 2022	Jun. 30, 2021	Dec. 31, 2015
Liability Related to Sale of Future Royalties
Non-cash royalty revenue related to the sale of future royalties			$ 5,590	$ 31,721
KADCYLA
Liability Related to Sale of Future Royalties
Percentage of royalty payments if applicable threshold is met					85%
IRH | KADCYLA
Liability Related to Sale of Future Royalties
Percentage of royalty payments					100%
Percentage of royalty payments if applicable threshold is met					15%
Transaction costs for royalty agreements					$ 5,900
Change in liability related to sale of future royalties
Liability related to sale of future royalties, net - beginning balance			41,044
Proceeds from sale of future royalties, net			200,000		200,000
Royalty payments received and paid			(6,537)
Non-cash interest expense recognized			2,327
Liability related to sale of future royalties, net - ending balance			$ 36,834
Effective annual interest rate			10.50%
Current effective interest rate			10.6
IRH | KADCYLA | Maximum
Liability Related to Sale of Future Royalties
Royalties threshold					260,000
IRH | KADCYLA | Minimum
Liability Related to Sale of Future Royalties
Royalties threshold					$ 235,000
OMERS | KADCYLA
Liability Related to Sale of Future Royalties
Percentage of royalty payments	100%
Non-cash royalty revenue related to the sale of future royalties	$ 65,200	$ 500
Contingent broker fees	1,500
Net proceeds from sale of residual rights to receive royalty payments	$ 65,200	$ 8,000
Roche
Liability Related to Sale of Future Royalties
Period in arrears to receive royalty reports and payments related to sales of Kadcyla			3 months
Roche | KADCYLA
Liability Related to Sale of Future Royalties
Non-cash royalty revenue related to the sale of future royalties			$ 13,500	$ 32,200

Income Taxes (Details)

Income Taxes (Details)	6 Months Ended
	Jun. 30, 2022
Tax Cuts and Jobs Act (TCJA)
Capitalize research and development expenses, amortization period	5 years
Capitalize research and experimentation expenses, amortization period	15 years

Capital Stock (Details)

Capital Stock (Details) $ / shares in Units, $ in Thousands			1 Months Ended	6 Months Ended
	Aug. 11, 2021 USD ($) $ / shares shares	Dec. 09, 2016	Dec. 31, 2021 USD ($) $ / shares shares	Jun. 30, 2022 USD ($) shares	Jun. 30, 2021 USD ($) shares
Stock-based compensation disclosure
Proceeds from issuance of common stock under stock plans | $				$ 1,031	$ 1,664
Exercise price | $ / shares			$ 6.60
Warrant exercise price | $ / shares			0.01
Pre-Funded Warrants
Stock-based compensation disclosure
Exercise price | $ / shares			$ 6.59
Threshold percentage of common stock owned that limits the number of warrants exercised	9.99
Maximum percentage upon at least 61 days prior notice from the investor to the Company	19.99
RA Capital Healthcare Fund, L.P. | Pre-Funded Warrants
Stock-based compensation disclosure
Pre-Funded warrants issued to purchase shares | shares			16,000,000
Redmile Group LLC | Pre-Funded Warrants
Stock-based compensation disclosure
Pre-Funded warrants issued to purchase shares | shares			11,363,636
Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares) | shares				8,670,000
Securities Purchase Agreement | Pre-Funded Warrants
Stock-based compensation disclosure
Proceeds from issuance of common stock under stock plans | $			$ 169,300
Securities Purchase Agreement | RA Capital Healthcare Fund, L.P. | Pre-Funded Warrants
Stock-based compensation disclosure
Pre-Funded warrants issued to purchase shares | shares	5,434,782
Exercise price | $ / shares	$ 5.51
Warrant exercise price | $ / shares	$ 0.01
Aggregate gross proceeds | $	$ 29,700
Compensation Policy for Non-Employee Directors | Stock options
Stock-based compensation disclosure
Stock options granted to directors (in shares) | shares				322,000	352,000
Non-employee directors-initial grant | Deferred share units
Stock-based compensation disclosure
Vesting period		3 years
Non-employee directors-first anniversary | Deferred share units
Stock-based compensation disclosure
Vesting period		1 year

Leases (Details)

Leases (Details) $ in Thousands	6 Months Ended		12 Months Ended
	Jun. 30, 2022 USD ($) ft² lease	Jun. 30, 2021 USD ($)	Dec. 31, 2020 ft² lease
Lessee, Lease, Description [Line Items]
Number of real estate leases | lease	1
Leasehold impairment charge	$ 0
Sublease income	2,200	$ 2,400
Sub Lessee Lease Incentive Payable	3,500
Payment of Sub Lessee Lease Incentive	1,800
Sublease Minimum Future Rental Payment, Receivable Forgiven	$ 2,100
830 Winter Street, Waltham, MA
Lessee, Lease, Description [Line Items]
Area of space leased | ft²	120,000
Number of executed sub-lease spaces | lease			4
Area of executed sublease space | ft²			65,000

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	3 Months Ended	6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2022 USD ($)
Research Collaboration Agreement
Collaborations and Manufacturing Commitments
Manufacturing commitment	$ 2.8	$ 2.8
Term of agreement		3 years
Non refundable upfront amount	7.5	$ 7.5
Agreement termination notice period		90 days
In-process and future manufacturing of antibody, drug substance, and cytotoxic agents
Collaborations and Manufacturing Commitments
Noncancelable obligations under several agreements	13	$ 13
Minimum
Collaborations and Manufacturing Commitments
Manufacturing commitment	$ 45.1	$ 45.1

Related Party Transactions (Det

Related Party Transactions (Details) $ in Millions	6 Months Ended
	Jun. 30, 2022 USD ($)
Related Party Transactions [Abstract]
Payments to related party	$ 3