PROPRIETARY INFORMATION, INVENTIONS, AND COMPETITION AGREEMENT

Exhibit 10.15

PROPRIETARY INFORMATION, INVENTIONS, AND COMPETITION AGREEMENT

AGREEMENT, dated this 30th day of November 2006, by and between ImmunoGen, Inc., a Massachusetts corporation having its principal place of business at 128 Sidney Street, Cambridge, Massachusetts 02139 (the “Company”), and Mitchel Sayare, an individual residing at 2 Avery Street, Suite 27c, Boston, MA 02111 (“Employee”).

WITNESSETH:

WHEREAS, the Employee has been hired by the Company to perform certain services; and

WHEREAS, the Employee may be exposed, have access to, create or make contributions to the Proprietary Information as defined below and/or inventions of the Company;

NOW, THEREFORE, in consideration for the Company’s employment of the Employee, and for other good and valuable consideration the receipt and sufficiency of which is hereby acknowledged, the parties covenant and agree as follows:

1.             Acknowledgements. The Employee understands and acknowledges that:

(a)           As part of his/her services as an employee of the Company, he/she may be exposed or have access to, or make new contributions and inventions of value to, the past, present and future business, products, operations and policies of the Company.

(b)           His/Her position as an employee creates a relationship of confidence and trust between the Employee and the Company with respect to (i) information which is related or applicable to the Company’s Field of Interest (as defined in 1(c) below) and the manner in which the Company engages in business in such Field of Interest, and (ii) information which is related or applicable to the business of the Company or any client, customer, joint venture or other person with which the Company has a business relationship, (a ”Business Associate”), any of which information has been or may be made known to the Employee by the Company (including, without limitation, any member of the Company’s Scientific Advisory Board) or by any Business Associate of the Company, or any of which has been otherwise learned by the Employee as a result of or in connection with his/her service as an employee of the Company.

(c)           The Company possesses and will continue to possess information that has been created by, discovered by, developed by or otherwise become known to the Company (including, without limitation, information created, discovered, developed or made known by the Employee related to or arising out of his/her service as an employee of the Company) and/or in which property rights have been assigned or otherwise conveyed to the Company, which information has commercial value to its business interests and/or in the Field of Interest in which the Company is presently engaged or will be engaged.  The term “Field of Interest” shall mean the development of products based on monoclonal antibodies or other biological molecules capable of binding to specific tissue, or the conjugation of monoclonal antibodies or other biological molecules capable of binding to specific tissue with other substances, for use in the treatment, diagnosis or prevention of cancer and/or other diseases.  During an individual’s employment, the term “Field of Interest” may be expanded from time to time to include such other areas of therapy,

diagnosis or prevention as may be designated by the Company. All of the aforementioned information is hereinafter called “Proprietary Information.” By way of illustration, but not limitation, formulas, data, know-how, improvements, inventions, techniques, marketing plans, strategies, forecasts, and customer lists are Proprietary Information.

2.             Proprietary Information.

(a)           All Proprietary Information shall be the sole property of the Company and its successors and assigns, and the Company and its successors and assigns shall be the sole owner of all patents and other rights in connection therewith. The Employee hereby assigns to the Company any rights he/she may have or acquire in such Proprietary Information, and agrees to take such action and sign such documents from time to time as the Company reasonably requires to effect or confirm such assignment.

(b)           At all times, both during the term of this Agreement and thereafter until such information becomes known to the public, the Employee will, subject to the provisions of Section 3 hereof regarding publication, keep in confidence and trust all Proprietary Information and any other confidential information of the Company, and he/she will not use or disclose any Proprietary Information or anything relating to it without the prior written consent of the Company, except as may be necessary in the ordinary course of performing his/her duties as an employee of the Company or as required by law; provided that if disclosure is required by law, the Employee agrees to provide the Company with written notice of such disclosure obligation prior to making such disclosure and no more than two (2) days after the Employee learns of such disclosure requirement.

(c)           All documents, records, apparatus, equipment and other physical property, whether or not pertaining to Proprietary Information, furnished to the Employee by the Company or produced by the Employee or others in connection with the Employee’s services hereunder shall be and remain the sole property of the Company. The Employee will return and deliver such property to the Company as and when requested by the Company. Should the Company not so request at an earlier time, the Employee shall return and deliver all such property upon termination of his/her service as an employee to the Company for any reason, and the Employee will not take with him/her any such property or any reproduction of such property upon such termination.

3.             Inventions.

(a)           The Employee will promptly disclose to the Company, or any persons designated by it, all improvements, inventions, formulas, processes, techniques, know-how and data, whether or not patentable, made or conceived or reduced to practice or learned by him/her, either alone or jointly with others, related to or arising out of his/her position as an employee or which are related to or useful in the business of the Company, or result from tasks which have been or may be assigned to the Employee by the Company or result from use of premises owned, leased or contracted for by the Company (all said improvements, inventions, formulas, processes, techniques, know-how and data being hereinafter collectively called “Inventions”).

(b)           The Employee agrees that all Inventions shall be the sole property of the Company and its assigns, and the Company and its assigns shall be the sole owner of all patents and other rights in connection therewith. The Employee hereby assigns to the Company any rights he/she may have or acquire in such Inventions. The Employee further agrees as to

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all such Inventions to assist the Company in every reasonable manner (but at the Company’s expense) to obtain, and from time to time enforce, patents on said Inventions in any and all countries, and to that end the Employee will execute all documents for use in applying for and obtaining such patents thereon and enforcing the same, as the Company may desire, together with any assignments thereof to the Company or persons designated by it. The Employee’s obligation to assist the Company in obtaining and enforcing patents for such Inventions in any and all countries shall continue beyond the termination of his/her employment by the Company, but the Company shall compensate the Employee at a reasonable rate after such termination for time actually spent by him/her at the Company’s request on such assistance. In the event that the Company is unable for any reason whatsoever to secure the Employee’s signature to any lawful and necessary documents required to apply for or execute any patent application with respect to such an Invention (including renewals, extensions, continuations, divisions or continuations in part thereof), the