UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 8-K

CURRENT REPORT

PURSUANT TO SECTION 13 OR 15(d)

OF THE SECURITIES EXCHANGE ACT OF 1934

Date of Report (Date of earliest event reported): August 27, 2013

ImmunoGen, Inc.

(Exact name of registrant as specified in its charter)

830 Winter Street, Waltham, MA 02451

(Address of principal executive offices)  (Zip Code)

Registrant’s telephone number, including area code: (781) 895-0600

Check the appropriate box below if the Form 8-K filing is intended to simultaneously satisfy the filing obligation of the registrant under any of the following provisions (see General Instruction A.2. below):

o            Written communications pursuant to Rule 425 under the Securities Act (17 CFR 230.425)

o            Soliciting material pursuant to Rule 14a-12 under the Exchange Act (17 CFR 240.14a-12)

o            Pre-commencement communications pursuant to Rule 14d-2(b) under the Exchange Act (17 CFR 240.14d-2(b))

o            Pre-commencement communications pursuant to Rule 13e-4(c) under the Exchange Act (17 CFR 240.13e-4(c))

ITEM 5.02 — DEPARTURE OF DIRECTORS OR CERTAIN OFFICERS; ELECTION OF DIRECTORS; APPOINTMENT OF CERTAIN OFFICERS; COMPENSATORY ARRANGEMENTS OF CERTAIN OFFICERS

(a)  Not applicable.

(b)  On August 27, 2013, ImmunoGen, Inc. (the “Company”) announced that Gregory D. Perry, Executive Vice President and Chief Financial Officer, has provided notice of his intention to resign from the Company effective as of September 13, 2013.  In connection with Mr. Perry’s resignation, he and the Company will be entering into a Transition and Separation Agreement which provides, among other things, that the existing employment agreement between the Company and Mr. Perry will be terminated, and the Company will provide Mr. Perry a salary continuation benefit equal to twelve months of his current base salary.

(c)  Effective immediately following Mr. Perry’s departure, Daniel M. Junius, the Company’s President and Chief Executive Officer, will become acting chief financial officer (and principal financial officer and principal accounting officer) while a search is undertaken to hire Mr. Perry’s replacement.  There have been no changes to Mr. Junius’ current arrangements with the Company as a result of these additional responsibilities.

(d)  Not applicable.

(e)  See paragraph (b) above.

(f)  Not applicable.

ITEM 9.01. — FINANCIAL STATEMENTS AND EXHIBITS

(d)  The following exhibit is being furnished herewith:

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this report to be signed on its behalf by the undersigned hereunto duly authorized.

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Exhibit 99.1

Contacts

ImmunoGen, Inc. Announces Executive Change

Waltham, MA, August 27, 2013 — ImmunoGen, Inc. (Nasdaq: IMGN), a biotechnology company that develops novel anticancer therapeutics using its proprietary antibody-drug conjugate (ADC) technology, today announced that Gregory D. Perry, Executive Vice President and Chief Financial Officer, has provided notice of his intention to resign from the Company to pursue other interests. His resignation is effective September 13, 2013.

“I sincerely appreciate Greg’s service to ImmunoGen over the four years we have worked together,” commented Daniel M. Junius, President and Chief Executive Officer. “On behalf of the Company, I thank Greg for his many contributions and wish him well in his future endeavors.”

ImmunoGen is initiating a search to hire Mr. Perry’s replacement. In the interim, Mr. Junius will be the Company’s acting chief financial officer.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops targeted anticancer therapeutics. The Company’s proprietary ADC technology uses a tumor-targeting engineered antibody to deliver one of ImmunoGen’s highly potent cancer-cell killing agents specifically to tumor cells. The most advanced compound using ImmunoGen’s TAP technology, Kadcyla®, is marketed in the US by Genentech, a member of the Roche Group, and undergoing regulatory review in the European Union and Japan. ImmunoGen has four wholly owned clinical-stage compounds, with additional compounds in the clinic through partnerships. More information about ImmunoGen can be found at www.immunogen.com.

Kadcyla® is a trademark of Genentech.

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