Imatinib mesylate for the treatment of hypereosinophilic syndromes.

Hypereosinophilic syndromes (HES) define several distinct entities, all of which show blood and tissue hypereosinophilia and end-organ secondary manifestations. From a clinical and pathogenic perspective, the best characterized are the myeloproliferative and lymphoproliferative variants. While there are several therapies available for the treatment of HES, such as corticosteroids, IFNalpha and cytotoxic agents, there remains a high incidence of side effects and inconsistent efficacy. Abnormal tyrosine kinase resulting from the FIP1L1PDGFRA fusion gene is found in many patients with myeloproliferative variant, and is currently best targeted therapeutically with imatinib mesylate, a tyrosine kinase inhibitor. However, complete hematological remissions obtained with this compound in patients without this defect suggest that it could be effective in other subtypes of HES.