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.