Chronic eosinophilic leukaemia, not elsewhere classified

**Definition:** A chronic myeloproliferative neoplasm characterised by persistent eosinophilia in the blood, bone marrow and peripheral tissues. Organ damage occurs as a result of leukaemic infiltration or the release of cytokines, enzymes or other proteins by the eosinophils. Chronic eosinophilic leukaemia, not otherwise specified excludes patients with a Ph chromosome, BCR-ABL1 fusion gene or rearrangement of PDGFRA, PDGFRB or FGFR1.