Blueprint Medicines announced new Phase 1 clinical data for BLU-285, a potent and highly selective KIT and PDGFRα inhibitor in development as a potential treatment for patients with advanced gastrointestinal stromal tumors (GIST). The data confirm and build upon data previously presented for BLU-285 in patients with advanced GIST, demonstrating robust clinical activity and a favorable safety profile. The data showed 67 percent of patients with heavily pretreated KIT-driven GIST treated with 300 to 400 mg of BLU-285 once daily (QD) had radiographic tumor reductions. In this population, the data also showed an objective response rate (ORR) of 17 percent and median progression free survival (PFS) of 11.5 months. In patients with PDGFRα-D842 driven GIST, the data showed an ORR of 71 percent and an estimated 12-month PFS of 78 percent. BLU-285 was well-tolerated, and most adverse events (AEs) reported by investigators were Grade 1 or 2.

As previously announced, Blueprint Medicines plans to pursue expedited development of BLU-285 in patients with PDGFRα D842V-driven GIST, and the Company is on track to initiate a global, randomized Phase 3 clinical trial of BLU-285 in third-line GIST in the first half of 2018, with the goal of supporting registration of BLU-285 in a broader GIST patient population. In addition, based on the strength of the data in patients with KIT-driven GIST, Blueprint Medicines announced today an expansion of the ongoing Phase 1 trial. The Company recently increased the enrollment target for patients previously treated with imatinib and at least one additional tyrosine kinase inhibitor (TKI) from 50 to 100 patients and added a new cohort to evaluate BLU-285 in second-line GIST.

"The updated BLU-285 data show robust clinical activity in a broad population of patients with advanced GIST," said Michael Heinrich, M.D., Professor of Medicine at Oregon Health & Science University and an investigator on the clinical trial. "In patients with PDGFRα-driven advanced GIST, the data for BLU-285 continue to be remarkable, particularly considering these patients have no effective treatment options. Importantly, I'm also very encouraged to see radiographic tumor reductions in two-thirds of patients with heavily pretreated GIST across all common KIT genotypes, as well as prolonged progression free survival in this population. Overall, these clinical results confirm recently published preclinical data showing activity across a spectrum of disease-relevant mutations and support clinical development of BLU-285 in a broad patient population."