1. Idiopathic Hypereosinophilic Syndrome (secondary HES), defined as a peripheral blood eosinophilia greater than 1,500 cells/µL for longer than 6 months, absence of other apparent aetiologies for eosinophilia and with or without signs and symptoms of organ involvement, irrespective to expression of any of imatinib targets (c-Kit receptor, PDGFR, bcr-abl receptor) on bone marrow cells.