UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

SCHEDULE 14A

Proxy Statement Pursuant to Section 14(a) of

the Securities Exchange Act of 1934

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Merrimack Pharmaceuticals, Inc.

(Name of Registrant as Specified in its Charter)

(Name of Person(s) Filing Proxy Statement, if Other Than the Registrant)

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	*** Exercise Your Right to Vote *** Important Notice Regarding the Availability of Proxy Materials for the Stockholder Meeting to Be Held on May 12, 2015.
	MERRIMACK PHARMACEUTICALS, INC.	Meeting Information
		Meeting Type:          Annual Meeting
		For holders as of:     March 18, 2015
		Date: May 12, 2015	Time: 3:00 PM, EDT
		Location:  Hotel Marlowe
		25 Edwin H. Land Boulevard
		Cambridge, Massachusetts 02141
	MERRIMACK PHARMACEUTICALS, INC. ONE KENDALL SQUARE SUITE B7201 CAMBRIDGE, MA 02139
		You are receiving this communication because you hold shares in the company named above. This is not a ballot. You cannot use this notice to vote these shares. This communication presents only an overview of the more complete proxy materials that are available to you on the Internet. You may view the proxy materials online at www.proxyvote.com or easily request a paper copy (see reverse side). We encourage you to access and review all of the important information contained in the proxy materials before voting.
		See the reverse side of this notice to obtain proxy materials and voting instructions.

—   Before You Vote   —

How to Access the Proxy Materials

	Proxy Materials Available to VIEW or RECEIVE:
	1. NOTICE, PROXY STATEMENT AND PROXY CARD     2. ANNUAL REPORT TO STOCKHOLDERS
	How to View Online:
	Have the information that is printed in the box marked by the arrow (located on the following page) and visit: www.proxyvote.com.
	How to Request and Receive a PAPER or E-MAIL Copy:
	If you want to receive a paper or e-mail copy of these documents, you must request one. There is NO charge for requesting a copy. Please choose one of the following methods to make your request:
	1) BY INTERNET:	www.proxyvote.com
	2) BY TELEPHONE:	1-800-579-1639
	3) BY E-MAIL*:	sendmaterial@proxyvote.com
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	Requests, instructions and other inquiries sent to this e-mail address will NOT be forwarded to your investment advisor. Please make the request as instructed above on or before April 28, 2015 to facilitate timely delivery.
	—   How To Vote   — Please Choose One of the Following Voting Methods
	Vote In Person: Many stockholder meetings have attendance requirements including, but not limited to, the possession of an attendance ticket issued by the entity holding the meeting. Please check the meeting materials for any special requirements for meeting attendance. At the meeting, you will need to request a ballot to vote these shares. Vote By Internet: To vote now by Internet, go to www.proxyvote.com. Have the information that is printed in the box marked by the arrow (located on the following page) available and follow the instructions. Vote By Mail: You can vote by mail by requesting a paper copy of the materials, which will include a proxy card.

Voting Items

	The Board of Directors recommends you vote FOR each director nominee:
	1.      Election of Directors
	Nominees:
	01)  Robert J. Mulroy  02)  Gary L. Crocker  03)  Gordon J. Fehr  04)  Vivian S. Lee, M.D., Ph.D.  05)  John Mendelsohn, M.D.	06)   Ulrik B. Nielsen, Ph.D. 07)   Michael E. Porter, Ph.D. 08)   James H. Quigley 09)   Russell T. Ray
	The Board of Directors recommends you vote FOR the following proposal:
	2.      To approve, on an advisory basis, our executive compensation.
	The Board of Directors recommends you vote 1 YEAR on the following proposal:
	3.      To recommend, on an advisory basis, the frequency of future advisory votes on our executive compensation.
	The Board of Directors recommends you vote FOR the following proposal:
	4.      To ratify the selection of PricewaterhouseCoopers LLP as our independent registered public accounting firm for the fiscal year ending December 31, 2015.
	NOTE:  The proxies are authorized to vote, in their discretion, upon such other business as may properly come before the meeting or any adjournment or postponement thereof.