ObjectiveTo explore the factors of affecting the prognosis of pancreatic ductal adenocarcinoma (PDAC) after radical resection based on the preoperative systemic immune-inflammation index (SII) and the controlling nutritional status (CONUT) score and to establish a prognostic prediction model.MethodsThe clinicopathologic data of patients diagnosed with PDAC from January 2014 to December 2019 in the Second Hospital of Lanzhou University were retrospectively analyzed. The X-tile software was used to determine the optimal cut-off value of SII. The Kaplan-Meier method was used to analyze survival. The Cox proportional hazards regression model was used to conduct multivariate analysis of prognostic factors of PDAC after radical surgery. R4.0.5 software was used to draw a nomogram prediction model of 1-, 2-, and 3-year survival rates, then evaluate the effectiveness of the prediction model and establish a web page calculator.ResultsA total of 131 patients were included in the study. The median survival time was 18.6 months, and the cumulative survival rates at 1-, 2-, and 3-year were 73.86%, 36.44%, and 11.95%, respectively. The optimal cut-off value of preoperative SII was 313.1, and the prognosis of patients with SII>313.1 was worse than SII≤313.1 (χ2=8.917, P=0.003). The results of multivariate analysis suggested that the age>65 years old, clinical stage Ⅲ and Ⅳ, preoperative SII>313.1, and CONUT score >4 were the independent factors influencing the prognosis (overall survival) for PDAC after radical resection (P<0.05). The internal verification consistency index (C-index) of the nomogram prediction model including age, clinical stage, preoperative SII, CONUT score and postoperative chemotherapy was 0.669. The survival predicted by the nomogram correction curve fitted well with the observed survival. The decision curve analysis showed that the nomogram prediction model had a wider clinical net benefit (Threshold probability was 0.05–0.95), and the web calculator worked well.ConclusionsAge, clinical stage, preoperative SII, CONUT score are independent influencing factors for prognosis after radical PDAC surgery. Nomogram prediction model included these independent influencing factors is more accurate and web calculator will be more convenient for doctors and patients.