Survival Outcomes of Two Phase 2 Studies of Adjuvant Chemotherapy with S-1 Plus Oxaliplatin or Capecitabine Plus Oxaliplatin for Patients with Gastric Cancer After D2 Gastrectomy

Background: Two phase 2 trials of oxaliplatin-containing adjuvant therapy for patients with gastric cancer (GC) after D2 gastrectomy were conducted in Japan. The SOXaGC trial evaluated the tolerability and safety of adjuvant therapy with S-1 plus oxaliplatin (SOX), whereas the J-CLASSIC trial evaluated the feasibility of adjuvant therapy with capecitabine plus oxaliplatin (CAPOX). Because both were studies that did not evaluate survival results as study end points, the authors evaluated the survival outcomes for the patients in the two trials. Methods: All 62 and 100 patients in the full analysis set of the SOXaGC and J-CLASSIC trials, respectively, were included in the current study. Their information about survival outcome was collected. The primary end point was relapse-free survival (RFS), and the secondary end point was overall survival (OS). Results: For the pathologic stage (pStage 2) patients treated with CAPOX, the 3-year RFS rate was 87.8% and the 3-year OS rate was 92.7%. For the pStage 3 patients treated with SOX and CAPOX, the 3-year RFS rates were respectively 70.9% and 67.8% (hazard ratio [HR], 0.93; 95% confidence interval [CI], 0.50–1.72), whereas the 3-year OS rates were respectively 75.7% and 79.3% (HR, 1.10; 95% CI, 0.54–2.26). Subgroup analysis showed significant interactions between the treatment (SOX vs. CAPOX) and both sex (male vs. female; P = 0.024) and histologic type (diffuse vs. other, P = 0.069). Conclusions: This exploratory analysis demonstrated that SOX and CAPOX are suggested to have similar efficacy for pStage 3 GC patients after D2 gastrectomy. Differences in the treatment effect according to sex and histologic type warrant further evaluation.