Immune Checkpoint Inhibitors in Sinonasal Squamous Cell Carcinoma: A Retrospective Study and Literature Review.

: Sinonasal squamous cell carcinoma (SNSCC) is a rare and aggressive malignancy, with limited treatment strategies in the recurrent or metastatic cases. Although immune checkpoint inhibitors (ICIs) have shown efficacy in head and neck cancers (HNCs), clinical data specific to SNSCC are scarce. This study aimed to evaluate the therapeutic efficacy and prognosis of ICIs in patients with SNSCC. : We conducted a retrospective review of 18 patients with pathologically confirmed SNSCC treated with nivolumab or pembrolizumab at Gifu University Hospital between May 2017 and December 2024. Treatment response was assessed using RECIST v1.1 criteria. Overall response rate (ORR) and disease control rate (DCR) were evaluated as treatment effects, and overall survival (OS) and progression-free survival (PFS) were evaluated as prognoses. Subgroup analyses were performed according to treatment regimen. : The ORR and DCR for all patients were 43.8% and 56.3%, respectively. Pembrolizumab-treated patients showed higher response rates (ORR: 66.7%; DCR: 83.3%) compared to those treated with nivolumab (ORR: 30%; DCR: 40%). Median OS and PFS were 21.5 and 7.9 months, respectively. Long-term durable responses exceeding two years were observed in several cases. Although pembrolizumab tended to result in better outcomes, no statistically significant difference was found between groups. Immune-related adverse events were infrequent and manageable. : This study suggests that a subset of patients with SNSCC may benefit from ICI therapy, particularly in combination with chemotherapy. Despite the rarity of SNSCC, accumulating clinical evidence-including prospective studies-is essential to establish standardized treatment strategies for this disease.