KIT and systemic mastocytosis: Imatinib is FDA-approved for a broad range of malignancies driven by dysregulated kinase activity, including Philadelphia chromosome–positive CML and acute lymphoblastic leukemia (ALL), KIT-mutant GIST, myelodysplastic/myeloproliferative disorders with PDGFR rearrangements, dermatofibrosarcoma protuberans, hypereosinophilic syndrome (HES), chronic eosinophilic leukemia, and aggressive systemic mastocytosis lacking the KIT D816V mutation.