Two cases of SMARCB1-deficient sinonasal undifferentiated carcinoma

Objective: To describe the clinical and pathological findings of two cases of SMARCB1-deficient sinonasal undifferentiated carcinoma and review the available literature. Patient: Case 1: An 82-year-old man was diagnosed with T4bN1M0 stage IVB SMARCB1-deficient sinonasal undifferentiated carcinoma. Local control was achieved by radiotherapy, but he developed pulmonary metastases. Case 2: A 37-year-old woman diagnosed with the same condition. Local control was achieved with chemoradiotherapy, but she developed pulmonary metastases and invasion of carcinoma under the skin of the head. Both patients died of pulmonary metastasis within one year of diagnosis. Conclusions: The disease has an extremely poor prognosis. SMARCB1 (INI1) immunohistochemistry has emerged as an important diagnostic tool to identify SMARCB1-altered neoplasms in routine surgical pathology practice.