The FIP1(14.7K-interacting protein 1)-like-1–platelet-derived growth factor receptor-α (FIP1L1-PDGFRA) fusion gene is a barometer distinguishing chronic eosinophilic leukemia (CEL) and other eosinophilic disorders, such as reactive eosinophilia (RE) and hypereosinophilic syndrome (HES) (10, 11). The gene discussed is PDGFRA; the disease is Chronic Eosinophilic Leukemia, Not Otherwise Specified.