Nature of Business and Plan of Operations	12 Months Ended
Dec. 31, 2017
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 of antibody‑drug, or ADC, therapeutics. The Company has generally incurred operating losses and negative cash flows from operations since inception, incurred a net loss of approximately $96.0 million during the year ended December 31, 2017, and has an accumulated deficit of approximately $1.03 billion as of December 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 December 31, 2017, the Company had $267.1 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources and expected future collaborator payments under existing collaborations will enable it to meet its operational expenses and capital expenditures for more than twelve months after these financial statements are issued. The Company may raise additional funds through equity or debt financings or generate revenues from collaborators through a combination of upfront license payments, milestone payments, royalty payments, research funding, and clinical material reimbursements. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate revenues from collaborators 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. In June 2016, the Company’s Board of Directors approved a change in the Company’s fiscal year from a fiscal year ending on the last day of June of each year to a calendar fiscal year ending on the last day of December of each year, effective January 1, 2017. Accordingly, in addition to financial statements as of and for the year ended December 31, 2017, these financial statements contain six month transitional financial statements as of and for the period ending December 31, 2016.

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, or ADC, therapeutics. The Company has generally incurred operating losses and negative cash flows from operations since inception, incurred a net loss of approximately $96.0 million during the year ended December 31, 2017, and has an accumulated deficit of approximately $1.03 billion as of December 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 December 31, 2017, the Company had $267.1 million of cash and cash equivalents on hand. The Company anticipates that its current capital resources and expected future collaborator payments under existing collaborations will enable it to meet its operational expenses and capital expenditures for more than twelve months after these financial statements are issued. The Company may raise additional funds through equity or debt financings or generate revenues from collaborators through a combination of upfront license payments, milestone payments, royalty payments, research funding, and clinical material reimbursements. There can be no assurance that the Company will be able to obtain additional debt or equity financing or generate revenues from collaborators 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.

In June 2016, the Company’s Board of Directors approved a change in the Company’s fiscal year from a fiscal year ending on the last day of June of each year to a calendar fiscal year ending on the last day of December of each year, effective January 1, 2017. Accordingly, in addition to financial statements as of and for the year ended December 31, 2017, these financial statements contain six month transitional financial statements as of and for the period ending December 31, 2016.