Background: After curative resection of gastric cancer with D2 lymph node dissection, postoperative adjuvant chemotherapy with S-1 or capecitabine plus oxaliplatin (XELOX) is considered to be standard therapy in Eastern countries. This study aimed to compare the efficacies of adjuvant S-1 and XELOX chemotherapy for gastric cancer patients after D2 dissection based on disease-free survival (DFS). Methods: This retrospective observational study was conducted at 29 tertiary hospitals in Korea. Of 1898 patients who underwent curative resection and received adjuvant chemotherapy for gastric cancer between February 2012 and December 2013, 1088 patients who met the eligibility criteria were enrolled in the study. After propensity score-matching, the 3-year disease-free survival rate (DFS) was used to compare efficacies directly between adjuvant XELOX and S-1 chemotherapies for patients with stage 2 or 3 gastric cancer after D2 gastrectomy. Results: The 3-year DFS rates for the S-1 and XELOX groups did not differ significantly among disease stages 2A, 2B, and 3A (all p > 0.05). However, the survival rates for the S-1 group were significantly lower than for the XELOX group for stage 3B (65.8% vs. 68.6%; p = 0.019) and stage 3C (48.4% vs. 66.7%; p = 0.002) gastric cancer. The hazard ratios (HRs) of S-1 chemotherapy for recurrence compared with XELOX for stages 3B and 3C were respectively 2.030 [95% confidence interval (CI), 1.110–3.715; p = 0.022] and 2.732 (95% CI 1.427–5.234; p = 0.002). Conclusions: Adjuvant XELOX chemotherapy was more effective than S-1 for patients with stage 3B or 3C gastric cancer after D2 lymph node dissection.
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