SMARCB1(SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily B, member 1)-deficient sinonasal carcinoma (SDSC) is a rare and highly aggressive malignant neoplasm of the head and neck region, accounting for 2.7% to 7.0% of primary sinonasal carcinomas. It exhibits a broad age distribution, non-specific clinical manifestations, and histomorphological features that closely mimic various other head and neck malignancies, posing significant diagnostic challenges for pathologists. This report details two SDSC cases treated in the Department of Patho-logy, Guangzhou First People's Hospital. Case 1 was a 75-year-old female who demonstrated combined loss of expression of SMARCB1 (Integrase Interactor 1, INI-1) and SMARCA2(SWI/SNF-related, matrix-associated, actin-dependent regulator of chromatin, subfamily A, member 2) (Brahma Homolog, BRM) proteins. The tumors were mainly located in the right maxillary sinus and nasal cavity. Case 2 was a 60-year-old male who exhibited loss of SMARCB1 (INI-1) expression only. The tumors were located in the left posterior ethmoid sinus. Histologically, both cases were predominantly composed of basaloid cells, interspersed with a minor population of cells exhibiting plasmacytoid/rhabdoid morphology characterized by eccentric nuclei. Case 1 featured extensive geographic tumor necrosis, with only scant residual viable tumor tissue. The clinical stage of both cases was cT₄N_xM₀ at the time of diagnosis. Follow-up: Case 1 received two cycles of induction chemotherapy combined with immunotherapy and died 3 months post-diagnosis. Case 2 underwent extended tumor resection followed by adjuvant therapy and died 12 months post-diagnosis. Comparative analysis revealed that the case with co-loss of SMARCB1 (INI-1) and SMARCA2 (BRM) expression was accompanied by more significant tumor necrosis morphologically and had a shorter survival time. According to literature and database searches worldwide, a total of 236 SDSC cases were reported, with an age range of 25-86 years and a male-to-female ratio of approximately 5:3 to 8:3. Among them, four cases (4/236) showed co-loss of SMARCB1 (INI-1) and SMARCA2 (BRM). However, there are still insufficient data to suggest that such cases have a worse survival prognosis. In conclusion, the overall prognosis of SDSC patients is poor, and there is currently no standard treatment plan. Morphological examination combined with SMARCB1 (INI-1) immunohistochemical testing is the key to definitive diagnosis, and combined detection of SWI/SNF complex member proteins helps identify co-loss cases. Although co-loss cases are rare and the significance of their survival prognosis analysis is unclear, more clinical experience is needed.