Hematological Neoplasm with Eosinophilia

Eosinophils in peripheral blood account for 0.3-5% of leukocytes, which is equivalent to 0.05-0.5 x 109/l. A count equal or above 0.5 x 109/l is considered eosinophilia, while a count equal or above 1.5 x 109/l is defined as hypereosinophilia. In bone marrow, eosinophilia is considered when eosinophils make up more than 6% of the total nuclear cells. In daily clinical practice, the most common causes of reactive eosinophilia are non- hematologic, whether non-neoplastic (allergic diseases, drugs, infections or immunological diseases) or neoplastic (solid tumors). Eosinophilia associated with a haematological malignancy may be reactive or secondary to the production of eosinophilopoietic cytokines, and this is mainly seen in lymphoid neoplasms (Hodgkin lymphoma, mature T-cell neoplasms, lymphoid variant of hypereosinophilic syndrome and B-acute lymphoblastic leukemia/lymphoma). Eosinophilia associated with a haematological malignancy may also be neoplastic or primary, derived from the malignant clone, usually in myeloid neoplasms or with origin in stem cell (myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions, acute myeloid leukemia with Core Binding Factor translocations, mastocytosis, myeloproliferative neoplasms, myelodysplastic/myeloproliferative neoplasms and myelodysplastic neoplasms). There are no concrete data in standardized cytological and cytometric procedures that could predict whether eosinophilia is reactive o clonal. The verification is usually indirect, based on the categorization of the accompanying hematologic malignancy. This review focuses on the broad differential diagnosis of haematological malignancies with eosinophilia.