SMARCB1 (INI1)-deficient sinonasal carcinoma: a newly described entity

SMARCB1 (INI1)-deficient sinonasal carcinoma is a recently described variant of sinonasal tract carcinoma characterized by complete loss of nuclear SMARCB1 (INI1). It is very rare and currently underdiagnosed because of a lack of awareness. Before the description of SMARCB1 (INI1)-deficient sinonasal carcinomas, these tumors were probably misclassified as various malignant neoplasms. To date, only 16 cases have been reported in the English literature. The authors herein report an additional case of SMARCB1 (INI1)-deficient sinonasal carcinoma of the maxillary sinus. An 86-year-old man presented with a painless, progressively enlarging mass on the left palate and intermittent epistaxis. Computed tomography displayed a large mass occupying the entire left maxillary sinus with destruction of maxillary bone and involvement of the left nasal cavity. The patient underwent radical left maxillectomy. The postoperative pathological diagnosis was sinonasal undifferentiated carcinoma. Immunohistochemistry for SMARCB1 (INI1) confirmed complete loss of nuclear SMARCB1 (INI1) expression in tumor cells, and the diagnosis of SMARCB1 (INI1)-deficient sinonasal carcinoma was finally established. With increased awareness and the use of SMARCB1 (INI1) immunohistochemistry, more SMARCB1 (INI1)-deficient carcinomas will be identified, leading to a more complete understanding of its pathologic and clinical features.