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. Here, KIT is linked to Chronic Eosinophilic Leukemia, Not Otherwise Specified.