SMARCA4-deficient undifferentiated tumor in the oral cavity: a rare case report and review of the literature.

SMARCA4-deficient undifferentiated tumor (SMARCA4-UT) is a rare and aggressive neoplasm in the oral and maxillofacial region. To our knowledge, only a single case of SMARCA4-UT involving the oral cavity has been reported, representing metastatic disease from a pulmonary primary. We report a case of a 66-year-old man who presented with a rapidly enlarging mass involving the left posterior maxillary mucosa with underlying bone destruction. Histopathologic examination revealed diffuse sheets of undifferentiated tumor cells with ovoid to epithelioid morphology. Immunohistochemistry demonstrated complete loss of nuclear SMARCA4 (BRG1) expression, supporting the diagnosis of SMARCA4-UT. The patient died approximately 10 days after biopsy, precluding further evaluation to definitively exclude metastatic disease. This case highlights the importance of recognizing SMARCA4-UT in the oral cavity to avoid misclassification and initiate prompt and appropriate clinical management, including assessment for metastatic disease.