This Employment Agreement (the “Agreement”), dated as of November 30, 2006 (the “ Effective Date
” ), is made by and between ImmunoGen, Inc., a Massachusetts corporation (the “ Company ”), and Walter A.
Blattler, Ph.D. (“ Executive ”). This Agreement is intended to confirm the understanding and set forth the
agreement between the Company and Executive with respect to Executive’s employment by the Company. In
consideration of the mutual promises and covenants contained in this Agreement, and for other good and valuable
consideration, the receipt and sufficiency of which are hereby mutually acknowledged, the Company and the
Executive hereby agree as follows:
1. Employment .
(a) Title and Duties . Subject to the terms and conditions of this Agreement, the Company
will employ Executive, and Executive will be employed by the Company, as Executive Vice President,
Science and Technology, reporting to the Chief Executive Officer. Executive will have the
responsibilities, duties and authority commensurate with said position. Executive will also perform such
other services of an executive nature for the Company as may be reasonably assigned to Executive from
time to time by the Chief Executive Officer or the Board of Directors of the Company (the “ Board ”).
(b) Devotion to Duties . For so long as Executive is employed hereunder, Executive will
devote substantially all of Executive’s business time and energies to the business and affairs of the
Company; provided that nothing contained in this Section 1(b) will be deemed to prevent or limit
Executive’s right to manage Executive’s personal investments on Executive’s own personal time,
including, without limitation, the right to make passive investments in the securities of (i) any entity which
Executive does not control, directly or indirectly, and which does not compete with the Company, or (ii)
any publicly held entity (other than the Company or its related entities) so l