RRBP1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified: • FIP1L1-PDGFRA(F/P)-associated HES, or F/P+ HES, for patients with clonal hypereosinophilia due to a sporadic hematopoiëtic stem cell chromosomal rearrangement resulting in fusion of two genes (FIP1L1 and PDGFRA) on 4q12; these patients are more appropriately classified as F/P+ chronic eosinophilic leukemia.