Concomitant KIT D816V+ bone marrow mastocytosis and FIP1L1::PDGFRA+ eosinophil neoplasm: a rare liaison

In a subset of patients with systemic mastocytosis (SM), an associated hematologic neoplasm (AHN) is identified. In most of these cases, a myeloid AHN such as a myeloproliferative neoplasm or myeloid leukemia, is diagnosed. Some AHN also present with eosinophilia or as an eosinophilic neoplasm. However, eosinophil-rich AHN expressing the FIP1L1::PDGFRA fusion gene are usually not detected in patients with KIT D816V+ SM. We report on a patient with a FIP1L1::PDGFRA + myeloid neoplasm associated with SM. The SM component of the disease was classified as KIT D816V+ bone marrow mastocytosis (BMM) and the FIP1L1::PDGFRA + neoplasm was classified as chronic eosinophilic leukemia. The patient suffered from severe mediator-related symptoms due to wasp venom allergy but did not have clinical signs or symptoms of a hypereosinophilic syndrome. Treatment with imatinib (100 mg/day) was followed by rapid resolution of eosinophilia and molecular remission with undetectable FIP1L1::PDGFRA. By contrast, BMM and mediator-related symptoms persisted.