FIP1L1 and systemic mastocytosis: Imatinib is thus approved for multiple indications such as Kit-mutant gastrointestinal stromal tumors (GIST), systemic mastocytosis, Ph+ acute lymphoblastic leukemia, myeloproliferative neoplasms with PDGFR gene-rearrangement, and hypereosinophilic syndrome with FIP1L1-PDGFRa.