Metastatic SMARCA4-Deficient Undifferentiated Carcinoma of the Oral Cavity: A Case Report and Review of Literature.

Purpose: SMARCA4-deficient high-grade malignancies are increasingly recognized across various anatomic sites, namely the genitourinary tract thorax, gastrointestinal tract, head and neck, and central nervous system. Within the head and neck region, the sinonasal tract is most commonly affected. These tumors are aggressive, often presenting with local or distant metastases at diagnosis, and median survival ranges from 4 to 7 months. We report a rare case of SMARCA4-deficient carcinoma presenting as a metastasis to the oral cavity, highlighting key histopathologic and clinical features.

Case report: A 63-year-old woman presented with a 3.0 × 2.0 × 2.0 cm exophytic mass involving teeth #25-28 and a 4 cm poorly defined radiolucency in the mandible. Histologically, the tumor was composed of diffuse sheets of large polygonal epithelioid cells with indistinct borders, pale eosinophilic cytoplasm, vesicular pleomorphic nuclei, prominent nucleoli, and numerous atypical mitotic figures and apoptotic bodies. Immunohistochemistry showed focal positivity for pankeratin, CAM5.2, and claudin-4. The tumor was negative for S100, SOX10, and SMARCA4 (BRG1), confirming SMARCA4-deficiency. A CT scan revealed a 5.5 cm mandibular lesion and a 16 cm right upper lobe lung mass, with additional nodules in the contralateral lung, thyroid, kidney, and widespread lymphadenopathy. The findings were consistent with a primary thoracic SMARCA4-deficient undifferentiated tumor with diffuse metastases. The patient died within two months of initial diagnosis of the oral metastasis.

Conclusion: To our knowledge, this is the first reported case of this unusual tumor metastasizing to the oral cavity. Given the aggressive nature and metastatic potential of these tumors, it is essential to evaluate for a distant primary malignancy when such a lesion is encountered in the head and neck.