High-grade transformation of low-grade biphenotypic sinonasal sarcoma: Radiological, morphophenotypic variation and confirmatory molecular analysis

Biphenotypic sinonasal sarcoma (BSNS) is a recently described spindle cell sarcoma with neural and myogenic differentiation which arises exclusively in the sinonasal region. A man presented with swelling of left eyelid, and history of resection of a low-grade spindle cell mesenchymal tumor of left sinonasal cavity performed 15 years before. The original diagnosis was synovial sarcoma. Current MRI showed left supraorbital mass with intracranial extension. IR biopsy confirmed recurrence, and a left orbital craniotomy was done. NGS identified PAX3-MAML3 fusion in both, current and original tumor. The sarcoma was reclassified as BSNS, recurrent, with higher grade transformation. While the morphology, phenotype and molecular signature were in keeping with BSNS, the tumor showed biological progression towards a high-grade sarcoma. High-grade transformation of low-grade BSNS has not been described so far. High-grade transformation was not appreciated at the time of initial diagnosis, and it occurred in the local recurrence 15 years after.