FIP1L1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified: Factor interacting with PAPOLA and CPSF1 (FIP1L1), fused with platelet-derived growth factor receptor α (PDGFRα), has been linked to several hematologic malignancies (hypereosinophilic syndrome, chronic eosinophilic leukemia, systemic mastocytosis) (123).