Abstract Lessons Learned The triple combination chemotherapy of SOXIRI (S-1/oxaliplatin/irinotecan) in patients with unresectable pancreatic ductal adenocarcinoma was an effective treatment that appeared to be better tolerated than the widely used FOLFIRINOX regimen. SOXIRI regimen may provide an alternative approach for advanced pancreatic cancer. Background In our previous phase I study, we determined the recommended dose of a biweekly S-1, oxaliplatin, and irinotecan (SOXIRI) regimen in patients with unresectable pancreatic ductal adenocarcinoma (PDAC). This phase II study was conducted to assess the safety and clinical efficacy in patients with unresectable PDAC. Methods Patients with previously untreated metastatic and locally advanced PDAC were enrolled. The primary endpoint was response rate (RR). Secondary endpoints were adverse events (AEs), progression-free survival (PFS), and overall survival (OS). Patients received 80 mg/m2 of S-1 twice a day for 2 weeks in alternate-day administration, 150 mg/m2 of irinotecan on day 1, and 85 mg/m2 of oxaliplatin on day 1 of a 2-week cycle. Results Thirty-five enrolled patients received a median of six (range: 2–15) treatment cycles. The RR was 22.8% (95% confidence interval [CI]: 10.4–40.1); median OS, 17.7 months (95% CI: 9.8–22.0); and median PFS, 7.4 months (95% CI: 4.2–8.4). Furthermore, the median OS in patients with distant metastasis was 10.1 months, whereas that in patients with locally advanced PDAC was 22.6 months. Major grade 3 or 4 toxicity included neutropenia (54%), anemia (17%), febrile neutropenia (11%), anorexia (9%), diarrhea (9%), and nausea (9%). There were no treatment-related deaths. Conclusion SOXIRI is considered a promising and well-tolerated regimen in patients with unresectable PDAC.