-- First Drug Candidate to Block Primary RET Fusion and Secondary Predicted Mutations and Induce Tumor Regression --

-- Novel discovery demonstrates RET fusions drive tumor growth in breast and colon cancers --

CAMBRIDGE, Mass., June 22, 2015 /PRNewswire/ -- Blueprint Medicines today announced the first preclinical data for its drug candidate BLU6864, a RET-specific kinase inhibitor. In preclinical studies, BLU6864 induced tumor regression in disease models driven by the primary RET fusion and all predicted secondary resistance mutations. RET is a key disease driver in multiple cancers. These data were presented at the EACR-AACR-SIC Special Conference on Anticancer Drug Action and Drug Resistance in Florence, Italy.

"One of the greatest challenges in treating cancer is cancer cell's ability to mutate and become resistant to treatment," said Alexander Drilon, M.D., a medical oncologist at Memorial Sloan Kettering Cancer Center. "RET fusions fuel the development and growth of multiple cancers, including lung and thyroid cancers. By targeting both the main cancer driver and predicted resistance mutations that arise from targeted therapy, we hope to provide patients with transformative medicines that mount a more effective attack on this subset of cancers and prevent recurrences of the disease."

In the preclinical data presented at the EACR-AACR-SIC Special Conference, BLU6864:

• Inhibited tumor growth and induced tumor regression at well-tolerated doses in a model of cancer driven by RET fusions,
• Inhibited tumor growth and induced tumor regression in a model harboring a resistance mutation that renders cancer cells insensitive to treatment with an approved multi-kinase inhibitor with activity against RET, and
• Spared VEGFR2, a kinase often inhibited together with RET and whose inhibition is associated with dose-limiting toxicities.

BLU6864 is one of the first kinase inhibitors designed specifically to inhibit RET. The drug candidate builds on Blueprint Medicines' work to identify novel drivers of disease. In addition to lung and thyroid cancers, the Company's scientists discovered that RET fusions are drivers in a subset of colon and breast tumors. Leveraging its expertise in genomics and structural biology, Blueprint Medicines was able to predict and validate the complete spectrum of future resistance mutations and designed drug candidates to target both the primary RET fusions and secondary treatment-resistant mutants.

In addition to BLU6864, Blueprint Medicines has two drug candidates on track to begin Phase 1 clinical trials in mid-2015, including BLU-554 in hepatocellular carcinoma and BLU-285 in metastatic and treatment-resistant gastrointestinal stromal tumors as well as systemic mastocytosis.

About Blueprint Medicines
Blueprint Medicines makes kinase drugs to treat patients with genomically defined diseases. Led by a team of industry innovators, Blueprint Medicines integrates a novel target discovery engine and a proprietary compound library to understand the blueprint of cancer and craft highly selective therapies. This empowers the Blueprint Medicines team to develop patient-defined medicines aimed at eradicating cancer.

Forward-Looking Statements
Various statements in this release concerning Blueprint Medicines' future expectations, plans and prospects, including without limitation, statements regarding Blueprint Medicines' ability to craft highly selective kinase inhibitors and deliver targeted medicines for patients with genomically defined cancers and statements concerning the timing of planned Phase 1 clinical trials for BLU-554 and BLU-285, constitute forward-looking statements for the purposes of the safe harbor provisions under The Private Securities Litigation Reform Act of 1995. In particular, it should be noted that the data on BLU6864 is early-stage data that may not be replicated in future pre-clinical studies or clinical trials. Any forward-looking statements in this press release are based on management's current expectations of future events and are subject to a number of risks and uncertainties. Actual results may differ materially from those indicated by these forward-looking statements as a result of various important factors, including, without limitation, the risk of delay of any planned clinical trials and/or development of Blueprint Medicines' drug product candidates, Blueprint Medicines' ability to successfully demonstrate the efficacy and safety of its drug product candidates, the pre-clinical and clinical results for its drug product candidates, which may not support further development of such drug product candidates, actions of regulatory agencies, which may affect the initiation, timing and progress of clinical trials, obtaining, maintaining and protecting intellectual property, Blueprint Medicines' ability to enforce its patents against infringers and defend its patent portfolio against challenges from third parties, competition from others developing products for similar uses, Blueprint Medicines' ability to manage operating expenses, Blueprint Medicines' ability to obtain additional funding to support its business activities and establish and maintain strategic business alliances and new business initiatives, Blueprint Medicines' dependence on third parties for various functions, the outcome of litigation, and unexpected expenditures, as well as those risks more fully discussed in the section entitled "Risk Factors" in Blueprint Medicines' Quarterly Report on Form 10-Q for the quarter ended March 31, 2015, as well as discussions of potential risks, uncertainties and other important factors in Blueprint Medicines' subsequent filings with the Securities and Exchange Commission. In addition, any forward-looking statements represent Blueprint Medicines' views only as of today and should not be relied upon as representing its views as of any subsequent date. Blueprint Medicines explicitly disclaims any obligation to update any forward-looking statements.

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SOURCE Blueprint Medicines