Abstract:Objective To investigate the efficacy and safety of sintilimab combined with simultaneous integrated boost-intensity modulated radiation therapy（SIB-IMRT）for locally advanced nasopharyngeal cancer. Methods A retrospective analysis was conducted on data of 106 patients with advanced nasopharyngeal cancer in the 900th Hospital of the Joint Service Support Force of the Chinese People’s Liberation Army from April 2019 to December 2022.According to treatment regimen, the patients were assigned into the SIB-IMRT group（n=54, adopted SIB-IMRT only）and the study group（n=52, adopted sintilimab based on SIB-IMRT）. The recent efficacy, adverse reactions, level of tumor markers［carbohydrate antigen 125（CA125）, squamous cell carcinoma antigen（SCC-Ag）, and cytokeratin 19fragment antigen 21-1（CYFRA21-1）］, and mid-term survival were compared. Results The objective response rate of the short-term efficacy in the study group was higher than that in the SIB-IMRT group（86.54% vs 66.67%, χ²=5.804, P=0.016）. There was no significant difference in the incidence of otitis media（15.38% vs 12.96%）, mucosal injury（78.85% vs 75.93%）, skin injury（19.23% vs 16.67%）, and salivary gland injury（61.54% vs 57.41%）between study group and SIB-IMRT group（P＞0.05）. No grade Ⅳ adverse reaction was observed, all reactions were relieved after appropriate treatment. Both groups showed reduced serum CA125, SCC-Ag, and CYFRA21-1 after treatment（P＜0.05）, and the levels in the study group were lower than those in the SIB-IMRT group（P＜0.05）. The study group had a higher 2-year survival rate（84.62%）than SIB-IMRT group（62.96%）（log-rank χ²=4.348, P＜0.05）.Conclusion Sintilimab combined with SIB-IMRT for locally advanced nasopharyngeal cancer can effectively downregulate serum level of CA125, SCC-Ag, and CYFRA21-1, enhance anti-tumor efficacy and mid-term survival rate greatly. and does not increase the occurrence of adverse reactions.