Effect of duration of adjuvant chemotherapy with S-1 (6 versus 12 months) for resected pancreatic cancer: the multicenter clinical randomized phase II postoperative adjuvant chemotherapy S-1 (PACS-1) trial

Background: Six months of adjuvant chemotherapy with S-1 is standard care for resected pancreatic cancer in Japan; however, the optimal duration has not been established. We aimed to evaluate the impact of duration of adjuvant chemotherapy with S-1. Methods: We performed a multicenter, randomized, open-label, phase II study. Patients with histologically proven invasive pancreatic ductal carcinoma, pathological stage I–III, and no local residual or microscopic residual tumor were eligible. Patients were randomized 1:1 to receive 6 or 12 months of adjuvant chemotherapy with S-1. The primary endpoint was 2-year overall survival (OS). Secondary endpoints were disease-free survival (DFS) and feasibility. Results: A total of 170 patients were randomized (85 per group); the full analysis set was 82 in both groups. Completion rates were 64.7% (6-month group) and 44.0% (12-month group). Two-year OS was 71.5% (6-month group) and 65.4% (12-month group) (hazard ratio (HR): 1.143; 80% confidence interval (CI): 0.841–1.553; P = 0.5758). Two-year DFS was 46.4% (6-month group) and 44.9% (12-month group) (HR: 1.069; 95% CI: 0.727–1.572; P = 0.6448). In patients who completed the regimen, 2-year DFS was 56.5% (6-month group) and 75.0% (12-month group) (HR: 0.586; 95% CI: 0.310–1.105; P = 0.0944). Frequent (≥ 5%) grade ≥ 3 adverse events comprised anorexia (10.5% in the 6-month group) and diarrhea (5.3% vs. 5.1%; 6- vs. 12-month group, respectively). Conclusions: In patients with resected pancreatic cancer, 12 months of adjuvant chemotherapy with S-1 was not superior to 6 months regarding OS and DFS.