SMARCB1-deficient sinonasal carcinoma with oral involvement: A potential mimicker of salivary-type carcinomas

SMARCB1-deficient sinonasal carcinoma is a rare sinonasal malignancy characterized by loss if INI1 expression on immunohistochemistry due to biallelic loss of SMARCB1 gene. Oral involvement is a an exceedingly unusual event. We present a 59-year-old woman with a destructive swelling covered by an ulcerated mucosa in the left posterior hard palate and alveolar ridge. Computed tomography scan demonstrated a tumor filling the left maxillary sinus with extension to the inferior nasal turbinate, alveolar process, and adjacent soft tissues. A biopsy performed from the oral aspect of the lesion revealed a basaloid tumor with rhabdoid/plasmacytoid cells, features that overlap with salivary-type carcinomas. Immunohistochemical analysis showed neoplastic cells positive to AE1/AE3 and p63, but negative to 34βE12, p16, chromogranin, synaptophysin, NUT, CD99, myogenin, smooth muscle actin, HMB45, S100 protein, androgen receptor, and TTF1. INI1 was also negative in neoplastic cells, but its expression was retained in stromal cells. The final diagnosis of SMARCB1-deficient sinonasal carcinoma was established. In conclusion, SMARCB1-deficient sinonasal carcinoma may infiltrate the oral cavity mimicking salivary-type carcinomas. A correlation of clinical, radiological, microscopical, and immunohistochemical aspects, the latter mainly represented by INI1 negativity, is mandatory to reach the appropriate diagnosis.