Biphenotypic Sinonasal Sarcoma with a Novel PAX7::PPARGC1 Fusion: Expanding the Spectrum of Gene Fusions Beyond the PAX3  Gene

AbstractBiphenotypic sinonasal sarcoma (BSNS) is a rare low-grade malignancy occurring in the sinonasal tract that is characterized by dual neural and myogenic differentiation. Rearrangements involving thePAX3 gene, usually withMAML3, are a hallmark of this tumor type and their identification are useful for diagnosis. Rarely, aMAML3 rearrangement without associatedPAX3 rearrangement has been described. Other gene fusions have not been previously reported. Herein, we report a 22 year-old woman with a BSNS harboring a novel gene fusion involving thePAX7 gene (specificallyPAX7::PPARGC1A), which is a paralogue ofPAX3. The histologic features of the tumor were typical with two exceptions: a lack of entrapment of surface respiratory mucosa and no hemangiopericytoma-like vasculature. Immunophenotypically, the tumor was notably negative for smooth muscle actin, which is usually positive in BSNS. However, the classic S100 protein-positive, SOX10-negative staining pattern was present. In addition, the tumor was positive for desmin and MyoD1 but negative for myogenin, a pattern that is common among BSNS with variant fusions. Awareness of the possibility ofPAX7 gene fusions in BSNS is important as it may aid in the diagnosis ofPAX3 fusion negative tumors.
Source: Head and Neck Pathology - Category: Pathology Source Type: research