Koshyk, OlenaMeyer, AndersKlubíčková, NatálieMosaieby, Elaheh2024-12-262024-12-262023-01-31Meyer A, Klubíčková N, Mosaieby E, Grossmann P, Kalmykova A, Koshyk O, Michal M. Biphenotypic sinonasal sarcoma with PAX3::MAML3 fusion transforming into high-grade rhabdomyosarcoma: report of an emerging rare phenomenon. Virchows Arch. 2023 Apr;482(4):777-782. doi: 10.1007/s00428-023-03501-0. Epub 2023 Jan 31. PMID: 36719455; PMCID: PMC10067655.10.1007/s00428-023-03501-0https://ir.kmu.edu.ua/handle/123456789/694We report a case of a 67-year-old male patient with a sinonasal tumor that showed areas of classic biphenotypic sinonasal sarcoma (BSNS) which in some sections sharply transitioned into high-grade rhabdomyosarcoma. Immunohistochemically, the conventional BSNS parts showed S100 protein, SMA, PAX7, and focal MyoD1 expression, whereas desmin and myogenin were negative. In contrast, the cells in high-grade areas expressed desmin, MyoD1, myogenin, and PAX7, while being negative for S100 protein and SMA. Using the Archer FusionPlex assay, the classical PAX3::MAML3 gene fusion was detected. FISH for PAX3 and MAML3 confirmed a break of these genes in both components. Despite aggressive therapy, the tumor progression resulted in the patient's death. The herein presented case, together with 2 previously published cases of BSNS with high-grade transformation, helps to better understand this novel phenomenon. Although the risk for such transformation appears low, it has important clinical and diagnostic implications which are discussed.en-USBiphenotypic sinonasal sarcomaHigh-grade transformationPAX3::MAML3RhabdomyosarcomaArticle