Sinonasal undifferentiated carcinoma: clinicopathological spectrums and diagnosis reappraisal.

Sinonasal undifferentiated carcinoma (SNUC) is defined as undifferentiated carcinoma of the sinonasal tract without glandular or squamous features and not otherwise classifiable. SNUC is a rare tumor, with a long list of differential diagnoses, and often poses a considerable diagnostic challenge. In addition, recent advances in molecular and immunohistochemistry techniques have recognized several new entities that were previously included in the SNUC category. These include SMARCB1 (INI-1)-deficient carcinoma, NUT (nuclear protein in testis) carcinoma, adamantinoma-like Ewing sarcoma, and the most recently described and rarer SMARCA4 (BRG)-deficient carcinoma. In this study, we retrospectively reviewed 11 cases with an original diagnosis of SNUC. We found that a significant portion of those cases can be reclassified into specific entities, with potential impact on therapy and prognosis because of misclassification in 2 of these cases.