Blu-285 is a potent and selective inhibitor for hematologic malignancies with KIT Exon 17 Mutations. BLU-285 has demonstrated biochemical in vitro activity on the KIT exon-17 mutant enzyme, KIT D816V. Cellular activity of BLU-285 on KIT D816 mutants was measured by autophosphorylation in the human mast cell leukemia cell line HMC1.2, and the P815 mouse mastocytoma cell line with IC50= 4 and 22 nM, respectively. In vivo BLU-285 was well tolerated and has demonstrated dose-dependent antitumor efficacy. Complete tumor growth inhibition and ≥ 75% KIT kinase inhibition was observed with 10 mg/kg once daily, oral dosing of BLU-285 in the aggressive KIT exon 17 mutant driven P815 mastocytoma model grown as a solid tumor allograft as well as in a disseminated model of the disease. BLU-285 was also well tolerated in this in vivo model and had no adverse effects on body weight at either dose.