Biphenotypic Sinonasal Sarcoma with a Novel PAX3::FOXO6 Fusion: A Case Report and Review of the Literature

Background Biphenotypic sinonasal sarcoma (BSS) is a low-grade, locally aggressive sarcoma unique to the sinonasal region. BSS is most common in middle aged patients and affects women more frequently than men. It is characterized by a bland spindled cell proliferation with neural and myogenic differentiation. BSS are usually associated with rearrangement t(2;4)(q35;q31.1) resulting in a PAX3::MAML3 fusion. Less commonly, other genes are found in combination with PAX3 and some cases reported in the literature have an unknown fusion partner. Methods A 54-year-old man presented with nasal mass. Endoscopic resection showed a low-grade spindle cell neoplasm with morphologic features of BSS and immunohistochemical and next generation sequencing were performed to confirm the diagnosis. Results The tumor was positive for S100 and smooth muscle actin but negative for SOX10. Next generation sequencing demonstrated a novel PAX3::FOXO6 gene fusion. Conclusions Although a PAX3::FOXO6 gene fusion has never been reported, this finding combined with the morphologic and immunophenotypic features supports the diagnosis of supports the diagnosis of BSS.