e17505 Background: Stage IIIC1 with larger/more short lymph node diameters and IIIC2-IVA cervical cancer patients had a particularly poor prognosis. Clinical practices have found that stage IIIC1-IVA patients diagnosed with pelvic lymph node short diameter ≥ 1.5cm/number of positive lymph nodes ≥ 3, or paraaortic lymph node metastasis, had a higher recurrence rate and lower overall survival rate. The overall survival rate is approximately 29% -52%. Sequential systemic chemotherapy after concurrent chemoradiotherapy (CCRT) can not improve survival in such patients. However, the current research results on the combination of CCRT with immune checkpoint inhibitors for cervical cancer are not ideal, which may be due to the lack of stratified analysis. This study compared the efficacy and safety of CCRT and combined use of immune checkpoint inhibitors (non sequential) for stage IIIC1-IVA cervical cancer through the cohort analysis, and analyzed the prognostic factors. Methods: Patients diagnosed with stage IIIC1-IVA cervical cancer who underwent concurrent chemoradiotherapy from October 2019 to October 2022 were enrolled. Patients were divided into the study group (35 cases) receiving Sintilimab concurrently with chemoradiotherapy and the control group (35 cases) receiving standard treatment. The primary endpoints were the assessment of one-year progression-free survival (PFS), objective response rate (ORR), and associated influencing factors. Secondary endpoints included treatment-related adverse events (TRAEs). Results: The one-year PFS rates were 88.6% in the study group and 62.9% in the control group, showing a significant difference (χ2=6.293, P=0.012). The median PFS was not reached. The ORR for tumor response was 74.30% in the study group, significantly higher than the 51.43% in the control group (P=0.048). Univariate analysis identified tumor maximum diameter (p = 0.01) and concurrent use of ICIs (p = 0.039) as prognostic factors for PFS. Multivariate Cox analysis also revealed tumor maximum diameter (p = 0.0121) and concurrent use of ICIs (p=0.049) as independent predictors of PFS. The most common TRAEs in both groups included leukopenia, decreased appetite, nausea/vomiting, and fatigue, with no significant differences in incidence (P>0.050). Grade ≥3 TRAEs were most frequently leukopenia (47.5%) and thrombocytopenia (17.1%) in the study group and leukopenia (51.4%) in the control group. All adverse reactions were alleviated after symptomatic treatment, dose reduction, or discontinuation, and no TRAE-related deaths occurred. Conclusions: In patients with stage IIIC1-IVA cervical cancer undergoing definitive concurrent chemoradiotherapy, the addition of ICIs may improve patient survival with manageable safety.