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.