Case report: PATZ1::FLT3 fusion in a FLT3-rearranged myeloid/lymphoid neoplasm with eosinophilia showing a (1;22;13;5) (q25;q12;q12;q34)- translocation

FLT3 -rearranged myeloid/lymphoid neoplasm with eosinophilia is a rare, aggressive blood cancer driven by a faulty gene fusion involving a tyrosine kinase; it affects both myeloid and lymphoid blood cells and is accompanied by high levels of eosinophils. Here, we report a POZ/BTB and AT hook containing zinc finger 1 ( PATZ1 ) ::FLT3 fusion arising from a four-way translocation, t(1;22;13;5)(q25;q12;q12;q34), found as the sole aberration in tumor cells from a 71-year-old patient presenting with marked eosinophilia, Löffler-like endocarditis, and concurrent classical Hodgkin lymphoma. The PATZ1::FLT3 fusion was confirmed by molecular analysis as an in-frame fusion retaining the tyrosine kinase domains of FLT3 . Although PATZ1::FLT3 has been previously reported, its occurrence in a patient with marked eosinophilia, Löffler-like endocarditis, and concurrent classical Hodgkin lymphoma highlights the clinical and biological complexity of FLT3 -rearranged MLN-TK. This case further expands the molecular spectrum of FLT3 -rearranged myeloid/lymphoid neoplasms with eosinophilia, and the identification of a potentially targetable FLT3 rearrangement may also have therapeutic implications for similar eosinophilic neoplasms.