 Chronic eosinophilic leukemia, not otherwise specified (i.e.CEL, NOS), is a leukemia-inducing disorder in the eosinophil cell lineage that causes eosinophil blood counts greater than 1,500/μL.The most recent (2017) World health organization criteria specifically excludes from this disorder hypereosinophilia/eosinophilia associated with "BCR-ABL1" fusion gene-positive chronic myeloid leukemia, polycythemia vera, essential thrombocytosis, primary myelofibrosis, chronic neutrophilic leukemia, chronic myelomonocytic leukemia, atypical chronic myelogenous leukemia, clonal eosinophilias involving gene rearrangements of "PDGFRA", "PDGFRB", or "FGFR1", and chromosome translocations that form "PCM1-JAK2", "ETV6-JAK2", or "BCR-JAK2" fusion genes.