Nature of Business and Plan of Operations	3 Months Ended
Mar. 31, 2017
Nature of Business and Plan of Operations
Nature of Business and Plan of Operations	IMMUNOGEN, INC. NOTES TO CONSOLIDATED FINANCIAL STATEMENTS March 31, 2017 A.Nature of Business and Plan of Operations ImmunoGen, Inc. (the Company) was incorporated in Massachusetts in 1981 and is focused on the development of antibody-drug conjugates, or ADCs, for the treatment of cancer. In August 2014, the FASB issued ASU 2014‑15, Presentation of Financial Statements-Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. (ASU 2015-14). Under the new standard, management must evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the financial statements are issued. This standard was adopted by the Company at December 31, 2016. The Company has incurred operating losses and negative cash flows from operations since inception, incurred a net loss of approximately $17.3 million during the three months ended March 31, 2017, and has an accumulated deficit of approximately $949.9 million as of March 31, 2017. The Company has primarily funded these losses through payments received from its collaborations and equity and convertible debt financings. To date, the Company has no product revenue and management expects operating losses to continue for the foreseeable future. At March 31, 2017, the Company had $126.6 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources and expected future collaborator payments will enable it to meet its operational expenses and capital expenditures (operating plan) into the second quarter of calendar year 2018. Without such collaborator payments, the Company’s existing capital resources at March 31, 2017 would not be sufficient to support the current operating plan through May 5, 2018, which is twelve months after the date that the March 2017 financial statements were issued. Management expects to seek additional funds from collaboration partners through a combination of upfront license payments, milestone payments, royalty payments, research funding, and clinical material reimbursement or from equity or debt financings. Because those plans have not been finalized, receipt of additional funding is not considered probable under the new standard. If the Company does not obtain sufficient funds when needed, the Company expects it would scale back its operating plan by deferring or limiting some or all of its research, development or clinical projects, or initiate further reductions to its workforce. Because such contingency plans have not been finalized (because the specifics would depend on the situation at the time), such actions also are not considered probable for purposes of the new standard. Because, under the new standard, neither receipt of future collaboration payments, nor management’s contingency plans to mitigate the risk and extend cash resources through May 5, 2018, are considered probable, substantial doubt is deemed to exist about the Company’s ability to continue as a going concern. 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, collaboration arrangements, third‑party reimbursements and compliance with governmental regulations.

IMMUNOGEN, INC.

NOTES TO CONSOLIDATED FINANCIAL STATEMENTS

March 31, 2017

A.Nature of Business and Plan of Operations

ImmunoGen, Inc. (the Company) was incorporated in Massachusetts in 1981 and is focused on the development of antibody-drug conjugates, or ADCs, for the treatment of cancer.

In August 2014, the FASB issued ASU 2014‑15, Presentation of Financial Statements-Going Concern (Subtopic 205-40): Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. (ASU 2015-14). Under the new standard, management must evaluate whether there are conditions or events, considered in the aggregate, that raise substantial doubt about the Company’s ability to continue as a going concern within one year after the date that the financial statements are issued. This evaluation initially does not take into consideration the potential mitigating effect of management’s plans that have not been fully implemented as of the date the financial statements are issued. When substantial doubt exists under this methodology, management evaluates whether the mitigating effect of its plans sufficiently alleviates substantial doubt about the Company’s ability to continue as a going concern. The mitigating effect of management’s plans, however, is only considered if both (1) it is probable that the plans will be effectively implemented within one year after the date that the financial statements are issued, and (2) it is probable that the plans, when implemented, will mitigate the relevant conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued. Generally, to be considered probable of being effectively implemented, the plans must have been approved before the date that the financial statements are issued. This standard was adopted by the Company at December 31, 2016.

The Company has incurred operating losses and negative cash flows from operations since inception, incurred a net loss of approximately $17.3 million during the three months ended March 31, 2017, and has an accumulated deficit of approximately $949.9 million as of March 31, 2017. The Company has primarily funded these losses through payments received from its collaborations and equity and convertible debt financings. To date, the Company has no product revenue and management expects operating losses to continue for the foreseeable future. At March 31, 2017, the Company had $126.6 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources and expected future collaborator payments will enable it to meet its operational expenses and capital expenditures (operating plan) into the second quarter of calendar year 2018. Without such collaborator payments, the Company’s existing capital resources at March 31, 2017 would not be sufficient to support the current operating plan through May 5, 2018, which is twelve months after the date that the March 2017 financial statements were issued. Management expects to seek additional funds from collaboration partners through a combination of upfront license payments, milestone payments, royalty payments, research funding, and clinical material reimbursement or from equity or debt financings. Because those plans have not been finalized, receipt of additional funding is not considered probable under the new standard. If the Company does not obtain sufficient funds when needed, the Company expects it would scale back its operating plan by deferring or limiting some or all of its research, development or clinical projects, or initiate further reductions to its workforce. Because such contingency plans have not been finalized (because the specifics would depend on the situation at the time), such actions also are not considered probable for purposes of the new standard. Because, under the new standard, neither receipt of future collaboration payments, nor management’s contingency plans to mitigate the risk and extend cash resources through May 5, 2018, are considered probable, substantial doubt is deemed to exist about the Company’s ability to continue as a going concern.

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, collaboration arrangements, third‑party reimbursements and compliance with governmental regulations.