Reappraisal of sinonasal undifferentiated carcinoma: SMARCB1 (INI1)-deficient sinonasal carcinoma: a single-institution experience.

Sinonasal carcinomas are rare and of diverse histology, often involve critical anatomic structures, and are associated with an aggressive clinical course and poor prognosis. Differentiating these tumor types may have clinical impact as advances in entity-specific therapeutic intervention could increase survival and quality of life and occasionally result in a cure. Recently, a unique subset of sinonasal carcinomas characterized by basaloid/rhabdoid tumor morphology and loss of expression of SMARCB1 (INI1) was identified. We tested a total of 256 tumors including head and neck (n = 241) and thoracic (n = 15) tumors with basaloid/rhabdoid morphology for loss of expression of SMARCB1 (INI1) using full tissue sections and tissue microarrays. Among these, four tumors of the sinonasal tract were found to be SMARCB1 (INI1) deficient and were reclassified as SMARCB1 (INI1)-deficient sinonasal carcinomas. These tumors appear to be restricted to the sinonasal tract, and their unique clinical, morphological, and immunohistochemical features seem to warrant inclusion as a separate new entity among the existing high-grade sinonasal neoplasms. Separation from the other types of sinonasal malignancies is important as the identification of SMARCB1 (INI1) deficiency may provide a new target for novel treatment approaches and may ultimately lead to improved patient survival.