Of note, failure of the standard chemotherapeutic agents (steroids, hydroxyurea, and interferon alpha) will not be a prerequisite for participation in this protocol for the following reasons. 1) There is no approved therapy for HES. 2) steroid therapy in the myeloid subset of HES patients is generally ineffective. 3) Although hydroxyurea and interferon alpha are initially effective in most cases, a majority of patients become refractory to or intolerant of these agents within a relatively short period of time (less than 1 year). 4) Data from other myeloid neoplasms and disorders, including CML, suggest that interferon, imatinib mesylate, and ruxolitinib, but not hydroxyurea, are associated with cytogenetic remission. 5) The reported incidence and severity of side effects from imatinib mesylate in patients with CML and ruxolitinib in myelofibrosis and polycythemia vera appear comparable to (or less than) those associated with interferon alpha.