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Preliminary Proxy Statement

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Definitive Proxy Statement

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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 June 21, 2016 Meeting Information Meeting Type: Annual Meeting For holders as of: April 25, 2016 Date: June 21, 2016 Time: 3:00 PM EDT Location: Goodwin Procter LLP 53 State Street Boston, Massachusetts 02109 BLUEPRINT MEDICINES CORPORATION BLUEPRINT MEDICINES CORPORATION ATTN:NOMINATING AND CORPORATE GOVERNANCE COMMITTEE 38 SIDNEY STREET, SUITE 200 CAMBRIDGE, MA 02139 You are receiving this communication because you hold shares in the above named company. 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). See the reverse side of this notice to obtain proxy materials and voting instructions. We encourage you to access and review all of the important information contained in the proxy materials before voting. 0000287950_1 R1.0.1.25 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. The Notice, Proxy Statement and Proxy Card 2. Annual Report How to View Online: Have the information that is printed in the box marked by the arrow following page) and visit: www.proxyvote.com. How to Request and Receive a PAPER or E-MAIL Copy: (located on the 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 * If requesting materials by e-mail, please send a blank e-mail with the information that is printed in the box marked by the arrow g (located on the following page) in the subject line. 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 June 07, 2016 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 g 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. 0000287950_2 R1.0.1.25

Voting items The Board of Directors recommends you vote FOR each director nominee: 1. Election of Directors Nominees 01 Jeffery W. Albers 02 Mark Goldberg, M.D. 03 Nicholas Lydon, Ph.D. The Board of Directors recommends you vote FOR the following proposal: 2 Ratification of the appointment of Ernst & Young LLP as independent registered public accounting firm for the fiscal year ending December 31, 2016. 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.

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