Complex hypereosinophilia arising from post-polycythemia vera myelofibrosis: A case of imatinib-responsiveness.

The classical myeloproliferative neoplasms (MPNs) feature an overproduction of mature blood elements. Phenotypic conversion, including transformation to myelofibrosis (MF) in those with antecedent ET and PV is a feared complication. Hypereosinophilic syndromes (HESs), especially those with myeloproliferative variants, can display similar features, including organomegaly, marrow fibrosis, clonality, thrombotic tendencies, and acute myeloid leukemia (AML) transformation. However, this group of illnesses is typically clinically and molecularly distinct from the classical MPNs. We report a case of a 59-yr-old woman with complex hypereosinophilia in the setting of post-polycythemic myelofibrosis (post-PVMF), with multi-system end-organ damage characteristic of HES.