Ruxolitinib in Treating Patients With Hypereosinophilic Syndrome or Primary Eosinophilic Disorders

PRIMARY OBJECTIVES: I. To determine the overall hematologic response rate to ruxolitinib in patients with hypereosinophilic syndrome and primary eosinophilic disorders. SECONDARY OBJECTIVES: I. To determine safety profile of ruxolitinib in patients with hypereosinophilic syndrome and primary eosinophilic disorders. II. To determine the proportion of patients on corticosteroids who are able to become corticosteroid-independent and/or reduce the dose by \>= 50%. III. To evaluate the duration of response (DoR). IV. To evaluate the time-to-response (TTR). V. To evaluate progression-free survival (PFS) and overall survival.