Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusion: report of two cases with different clinical presentation.

Myeloid/lymphoid neoplasms with eosinophilia and tyrosine kinase gene fusions (M/LN-eo-TK) such as PDGFRA, PDGFRB, FGFR1, JAK2, FLT3 rearrangement and ETV6::ABL1 fusion include rare and heterogeneous clinical-pathological entities with some similarities, not always associated with peripheral eosinophilia. Accurate diagnosis and demonstration of the specific genetic substrate have important implications since target therapy is possibly available. Herein we report two cases showing different bone marrow features and clinical presentation. Recognition of eosinophilic granuloblasts prompted genetic analysis that showed PDGFRB (case 1) and PDGFRA (case 2) gene rearrangement. Diagnosis of M/LN-eo-TK may be challenging. Pathologists may be the first professionals to suspect the disorder and should be aware of the therapeutic implication. Accurate BOM marrow evaluation with a panel of immunohistochemical reactions, and specific molecular analyses are required for proper diagnosis.