Sinonasal EWSR1::POU2AF3 Sarcoma: a Case Report and Literature Review

We present the clinicopathologic and molecular characteristics of a rare sinonasal sarcoma with undifferentiated round cell and spindle morphology, defined by the EWSR1::POU2AF3 fusion. A 62-year-old male presented with nasal congestion. A polypoid lesion excised from the sinonasal cavity was initially diagnosed as 'glomangiopericytoma' at an external center, but recurred and was referred to our clinic four years later. Histopathological evaluation of primary and recurrent tumors showed pleomorphic spindle and round cell morphology with prominent nucleoli and thin-walled hemangiopericytomatous vessels. CD99 (MIC2) and CD117 (CKIT) were diffuse positivite while ß-catenin showed cytoplasmic/membranous expression. Pancytokeratin and EMA were focally positive. NKX2.2, DUX4, ETV4, BCOR, CCNB3, SS18-SSX, STAT6, CD34, and others were all negative. Next generation sequencing confirmed EWSR1::POU2AF3 fusion. This case exemplifies a rare, aggressive sinonasal sarcoma with EWSR1::POU2AF3 fusion, emphasizing its distinct morphology and challenging behaviour.