Therapeutic and Biological Effects of Imatinib Mesylate in Primary Hypereosinophilic Syndromes

Hypereosinophilic syndrome (HES), chronic eosinophilic leukaemia (CEL) and chronic idiopathic hypereosinophilia (CIH) are rare disorders characterized by chronic hypereosinophilia with possible damage to various organs due to eosinophilic infiltration and release of cytokines. The therapies of these diseases are largely unsatisfactory and based on the use of a variety of antiproliferative drugs such as corticosteroids, interferon-alfa, cyclosporine, vincristine or hydroxyurea. More often the responses are transient and patients need numerous treatment lines.

In 2001 Schaller et al reported the first case of a patient with HES resistant to conventional treatment that responded to imatinib mesylate. (Schaller, MGM 2001). After that, many authors described cases with hypereosinophilia that achieve a rapid response to Imatinib and in 2003 Cools et al identified a novel tyrosine kinase generated from the fusion of the Fip1-like 1 (FIP1L1) gene to the PDGFRalfa gene associated to hypereosinophilia.

The optimal dose of Imatinib in this setting of patients is still unknown; however, the demonstration of effective and safe clinical doses in a variety of currently studied malignant diseases, suggests that a dose of 100 mg/day increasing weekly of 100 mg/day (maximum dose 400 mg/day), may be employed.

We designed a phase II trial to investigate the clinical anti-proliferative activity, safety and tolerability of escalating doses of Imatinib (entry dose 100 mg/d)administered for 12 total weeks in HES, CEL and CIH patients.