Abstract
SWItch/Sucrose Non-Fermentable (SWI/SNF) -related matrix-associated actin-dependent regulator of chromatin (SMARC) subfamily B member 1 (SMARCB1) deficient sinonasal carcinoma (SdSNC) is a rare variant of sinonasal undifferentiated carcinoma (SNUC). A 72-year-old man was referred to our hospital with complaints of left facial pain and nasal obstruction. Computed tomography (CI) revealed a tumor 5.5 cm in size in the left nasal cavity. Atypical cells with eosinophilic cytoplasm proliferating as solid nests and exhibiting necrosis were observed and diagnosed as poorly differentiated carcinoma. Carbon ion radiotherapy was performed. Follow-up CI revealed multiple masses in both lungs. Partial resection of the right lung was performed. Proliferating atypical cells with clear-to-eosinophilic cytoplasm were observed and resembled those in the paranasal sinus tumor. Immunohistochemical analysis indicated a metastatic lung tumor derived from the SNUC revealed completely negative SMARCB1 expression in the nuclei of the tumor cells. SdSNC is difficult to diagnose. However, molecular targeted therapy may be useful. Thus, it is necessary and important to recognize this rare cancer accurately.