Myeloid or lymphoid neoplasms with eosinophilia and abnormalities of PDGFRA, PDGFRB or FGFR1

**Definition:** A group of rare myeloid or lymphoid neoplasms characterised by rearrangement of the platelet-derived growth factor receptor alpha (PDGFRA), platelet-derived growth factor receptor beta (PDGFRB), and fibroblast growth factor receptor-1 (FGFR1) genes, resulting in the formation of fusion transcripts and aberrant tyrosine kinase activity. Eosinophilia is a characteristic finding but it is not always present.