Imatinib Mesylate Treatment in Two Patients with Idiopathic Hypereosinophilic Syndrome

OBJECTIVE: To report 2 clinical cases of hypereosinophilic syndrome (HES) refractory to standard therapy and the variable responses to imatinib mesylate, and to review previously reported cases of imatinib mesylate use in the treatment of hypereosinophilia. case summaries: Two male patients were diagnosed with idiopathic HES complicated with organ involvement. Both were treated with imatinib mesylate after failing to respond to or being unable to tolerate standard therapy. In one patient, treatment with imatinib mesylate 100 mg/day produced resolution of symptoms and peripheral blood cell counts within 6 days. The patient has successfully maintained normal blood cell counts and has been without symptoms for more than one year after starting imatinib mesylate. The other patient failed to respond to imatinib mesylate even at the maximum dose (up to 400 mg/day). DISCUSSION: Imatinib mesylate was considered an appropriate alternative for standard therapy of HES based on the evidence that other treatments used for chronic myelogenous leukemia have also been successful in treating HES. Three small studies have supported this hypothesis. However, not all patients with HES respond to imatinib mesylate therapy. The cases presented here illustrate the marked difference. CONCLUSIONS: Imatinib mesylate has shown some promise in the treatment of HES. However, until the etiology of idiopathic hypereosinophilia and the role of imatinib mesylate in the resolution of this disease are determined, it will continue to be difficult to predict the responsiveness of a patient to imatinib mesylate therapy.