Standard versus delayed initiation of S-1 adjuvant chemotherapy after surgery for pancreatic cancer: a secondary analysis of a nationwide cohort by the Japan Pancreas Society

Background Based on the Japan Adjuvant Study Group of Pancreatic Cancer-01 results, S-1 adjuvant chemotherapy has been the standard in resected pancreatic ductal adenocarcinoma (PDAC) patients in Japan and elsewhere, initiated within 10 weeks after surgery. To assess the clinical impact of this timing, we conducted a secondary analysis of a nationwide survey by the Japan Pancreas Society. Methods A total of 3361 patients were divided into two groups: 2681 (79.8%) initiating the therapy within 10 weeks after surgery (standard) and 680 (20.2%) after 10 weeks (delayed). We compared recurrence-free survival (RFS) and overall survival (OS) using the log-rank test and Cox proportional hazards model with conditional landmark analysis between the groups. Results were verified by adjustment with inverse-probability-of-treatment weighting (IPTW) analysis. Results The median timing of S-1 adjuvant chemotherapy initiation was 50 days (interquartile range: 38–66). In the standard group, 5-year RFS and OS rates were 32.3–48.7%, respectively, compared with 25.0–38.7% in the delayed group. Hazard ratios (HRs) and 95% confidence intervals were 0.84 (0.76–0.93) for RFS ( p < 0.001) and 0.77 (0.69–0.87) for OS ( p < 0.001). The IPTW analysis yielded 5-year RFS rates of 32.1% and 25.3% in the standard versus delayed group, respectively [ HR = 0.86 (0.77–0.96), p < 0.001] and 5-year OS rates of 48.3% and 39.8%, respectively [ HR = 0.81 (0.71–0.92), p < 0.001]. Conclusions Initiation of S-1 adjuvant chemotherapy in resected PDAC patients within 10 weeks after surgery may offer survival benefit over later initiation.