Minimum 7‐Year Follow‐Up of a Prospective Phase II Trial of Preoperative S‐1 Plus Oxaliplatin Chemotherapy for Clinical Stage III Gastric Cancer

AIM: We report long-term outcomes from a prospective Phase II trial of two cycles of preoperative S-1 plus oxaliplatin (SOX) chemotherapy in patients with clinical Stage III gastric cancer (GC), with at least 7 years of follow-up for all surviving patients. METHODS: Patients received two cycles of preoperative SOX followed by laparoscopic D2 gastrectomy and postoperative adjuvant therapy. Overall survival (OS), relapse-free survival (RFS), treatment compliance, and clinically documented late adverse events were evaluated. Associations between clinicopathological factors and survival were explored using Kaplan-Meier analysis and the log-rank test. RESULTS: Thirty-four patients were analyzed. Preoperative SOX completion was 100%, with clinical and pathological response rates of 73.5% and 58.8%, respectively. R0 resection was achieved in 97.1%, and adjuvant therapy was initiated in 94.1% and completed in 61.8%. At analysis, 18 patients had died and 16 remained alive; all survivors had at least 7 years of follow-up and none were lost to follow-up. Five-year OS and RFS were 61.8% and 58.8%, respectively. In exploratory analyses, ypN0-1 status and a preoperative neutrophil-to-lymphocyte ratio < 4.3 were associated with better OS and RFS. No severe treatment-related late adverse events were documented during routine follow-up, although late toxicities were not systematically assessed. CONCLUSION: Two-cycle preoperative SOX was highly feasible, with high treatment compliance and favorable long-term outcomes in this prospective single-arm cohort. Associations of ypN status and preoperative neutrophil-to-lymphocyte ratio with long-term outcomes were exploratory and require validation in larger comparative studies. TRIAL REGISTRATION: UMIN000036139.