Response of idiopathic hypereosinophilic syndrome to treatment with imatinib mesylate.

Idiopathic hypereosinophilic syndrome (HES) is a rare hematologic disorder characterized by persistent eosinophilia with organ involvement. Patients with HES have a poor prognosis, but the disease course can be heterogeneous. Treatment of HES has included corticosteroids, chemotherapeutic agents such as cyclophosphamide, vincristine, hydroxyrea, and most recently interferon-alpha (IFN-alpha) which has shown long-term beneficial effects. We herein report on a patient with HES who had disease resistant to steroids, and chemotherapy with 2-chlorodeoxyadenosine and cytarabine, but who had a significant response after only 8 days of treatment with imatinib mesylate 100mg daily. The possible mechanism of response is discussed. This observation may lead to a better understanding of the pathophysiology of HES, and may provide a new form of effective therapy for the disease.