Heterogeneity of Response to Imatinib-Mesylate (Glivec) in Patients with Hypereosinophilic Syndrome: Implications for Dosing and Pathogenesis

Four cases of hypereosinophilic syndrome (HES) treated with the tyrosine-kinase inhibitor imatinib-mesylate are reported. The drug was effective in three patients, but a prolonged clinical and hematological remission was obtained only in one patient, due to appearance of resistance or poor tolerability in the other cases. The dose of imatinib necessary to achieve a response ranged from 100 to 600 mg/d. One patient with evidence of a clonal T-cell population did not respond at all. We confirm the efficacy of imatinib in HES, but we also underline that type and duration of response may be variable. This could be due to different pathogenetic mechanisms of the disease in single patients.