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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 18, 2019 BLUEPRINT MEDICINES CORPORATION Meeting Information Meeting Type: Annual Meeting For holders as of: April 22, 2019 Date: June 18, 2019 Time: 3:30 PM EDT Location: Blueprint Medicines Corporation 45 Sidney Street Cambridge, Massachusetts 02139 BLUEPRINT MEDICINES CORPORATION ATTN: TRACEY L. MCCAIN 45 SIDNEY STREET 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). 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. 0000421053_1 R1.0.1.18

Before You Vote How to Access the Proxy Materials Proxy Materials Available to VIEW or RECEIVE: Notice & Proxy Statement 2. Annual Report to Stockholders How to View Online: Have the information that is printed in the box marked by the arrow XXXX XXXX XXXX XXXX (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: BY INTERNET: www.proxyvote.com BY TELEPHONE: 1-800-579-1639 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 XXXX XXXX XXXX XXXX (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 04, 2019 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 XXXX XXXX XXXX XXXX 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. 0000421053_2 R1.0.1.18

Voting items 0000421053_3 R1.0.1.18 The Board of Directors recommends you vote FOR the director nominees in Proposal 1 and FOR Proposals 2 and 3. Election of Directors Nominees 01 Jeffrey W. Albers 02 Mark Goldberg, M.D. 03 Nicholas Lydon, Ph.D. To approve an advisory vote on named executive officer compensation. Ratification of the appointment of Ernst & Young LLP as independent registered public accounting firm for the fiscal year ended December 31, 2019. 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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