목적: The histological types of sinonasal malignancy are highly diverse, and many are difficult to differentiate. Sinonasal cancers that were difficult to differentiate have been classified as undifferentiated (UD) or poorly differentiated (PD) carcinoma. Advancements in molecular biology have led to reclassifying cancers previously grouped as UD into categories like NUT carcinoma. Among these, the 2022 5th edition of the WHO Classification of the Head and Neck has defined SWI/SNF complex-deficient carcinomas, characterized by the loss of one of the SWI/SNF complex genes, including two major subtypes: SMARCB1- and SMARCA4-deficient sinonasal carcinoma. We aim to provide a brief report on patients' clinical characteristics and prognosis with these rare tumors based on a retrospective analysis. 방법:We conducted a retrospective analysis of the clinical and pathological data of nine patients diagnosed with sinonasal cancer at Samsung Medical Center from June 2018 to January 2024. These patients specifically had SWI/SNF complex-deficient carcinoma, either SMARCB1 or SMARCA4. All patients were confirmed to have a loss of expression of SMARCB1 or SMARCA4 by immunohistochemistry. 결과:Six were female (66.67%) and three were male (33.33%), with a median age at diagnosis of 60 years (range, 42 - 74). According to the AJCC 8th staging, 7 patients (77.78%) were at T4 stage, 8 (88.89%) at N0, and 1 patient (11.11%) at N2. No distant metastasis was observed at diagnosis in any patient. Of the nine, 2 patients (22.22%) were initially diagnosed with poorly differentiated squamous cell carcinoma and 1 patient (11.11%) with olfactory neuroblastoma. Seven patients (77.78%) underwent curative treatment; 6 patients (66.67%) underwent definitive concurrent chemoradiation therapy (CCRT) due to surgically unresectable tumor extent, and 1 patient (11.11%) underwent adjuvant CCRT after surgery. The remaining 2 patients (22.22%) underwent palliative treatment due to systemic metastasis from a second primary cancer. The median period for the last follow-up was 4 months (range, 0 - 95), with 4 patients (44.44%) died from the disease, 3 patients (33.33%) alive with disease, 1 patient (11.11%) with no evidence of disease, and 1 patient currently receiving adjuvant treatment. Recurrence was observed in 4 patients (44.44%), with two (22.22%) having distant metastasis and the other two (22.22%) local recurrence. One patient (11.11%) was identified with progressive disease. The 1- year overall survival was 61%, and the 3-month overall survival was 76.2%. Two (22.22%) out of the total 9 patients died within one month of diagnosis due to rapid progression. 결론:Some cases of sinonasal UD carcinoma have been reclassified as SWI/SNF complex-deficient sinonasal carcinoma with the advancement of immunological markers. This retrospective analysis of SWI/SNF- deficient sinonasal carcinomas highlights the aggressive nature and poor prognosis of these rare tumors. Despite most patients receiving curative treatment, the high rate of recurrence (44.44%) and significant mortality (44.44%) within a short median follow-up period of 4 months underscore the challenges in managing this malignancy.