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 4, 2016

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 4, 2016, Dr. Charles Q. Morris, Executive Vice President and Chief Development Officer of ImmunoGen, Inc. (the “Company”), provided notice to the Company of his intention to resign from the Company, effective as of the close of business on September 2, 2016, in order to pursue another professional opportunity closer to his primary residence in Pennsylvania.

(c) — (f)  Not applicable.

ITEM 9.01. FINANCIAL STATEMENTS AND EXHIBITS

(d): The following exhibits are being filed 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 Announces Departure of Chief Development Officer

WALTHAM, MA, August 9, 2016 — ImmunoGen, Inc. (Nasdaq: IMGN), a leader in the expanding field of antibody-drug conjugates (ADCs) for the treatment of cancer, today announced that Charles Morris, MBChB, MRCP, Executive Vice President and Chief Development Officer, is leaving the Company effective September 2 to pursue an opportunity closer to his primary residence in Pennsylvania.

“Charlie has made a significant contribution to ImmunoGen over these past four years,” said Mark Enyedy, President and CEO. “He played a key role in building a strong development organization, including an experienced team led by our Chief Medical Officer and Vice President, Anna Berkenblit, MD, and our Vice President, Regulatory Affairs, Theresa Wingrove, PhD. Anna and Theresa will now report directly to me, as we advance our pipeline and initiate the Phase 3 study of mirvetuximab soravtansine before the end of the year. We wish Charlie the very best in his new role.”

“ImmunoGen is successfully implementing a speed-to-market strategy for our lead product candidate, mirvetuximab soravtansine, is accelerating a strong pipeline behind it, and continues to drive significant ADC innovations,” commented Dr. Morris. “I am proud of what we have accomplished with our portfolio and look forward to ImmunoGen’s continued success, as this talented development team advances these exciting ADC programs to benefit patients with cancer.”

About ImmunoGen, Inc.

ImmunoGen is a clinical-stage biotechnology company that develops targeted cancer therapeutics using its proprietary ADC technology. ImmunoGen’s lead product candidate, mirvetuximab soravtansine, is advancing to Phase 3 testing for FRα-positive platinum-resistant ovarian cancer, with a strong pipeline progressing behind it. ImmunoGen’s ADC technology is used in Roche’s marketed product, Kadcyla®, and in programs in development by partners Amgen, Bayer, Biotest, CytomX, Lilly, Novartis, Sanofi and Takeda.

Kadcyla® is a registered trademark of Genentech, a member of the Roche Group.