FGFR1 and Chronic Eosinophilic Leukemia, Not Otherwise Specified: In the 2008 revision of the World Health Organization (WHO) classification of myeloid neoplasms and acute leukemia, a specific group of patients with eosinophilia and gene rearrangements involving PDGFRA, PDGFRB, or FGFR1 were excluded from the diagnosis of CEL and classified as a separate entity, namely “myeloid and lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB, or FGFR1 (MLNE)”, which have distinct clinical and molecular features and respond well to tyrosine kinase inhibitors18.