Comparison of adjuvant capecitabine plus oxaliplatin (CAPOX) versus S-1 after gastrectomy: a population-based cohort study using a nationwide claims database

Although both capecitabine plus oxaliplatin (CAPOX) and S-1 are accepted as adjuvant chemotherapy following gastrectomy for gastric cancer, the better option between the two is still controversial. We conducted a retrospective nationwide cohort study using data from the National Health Insurance Service of Korea. We included patients who underwent gastrectomy for a primary diagnosis of gastric cancer between January 1, 2013, and December 31, 2018. The study compared the survival outcomes of patients who received postoperative chemotherapy based on S-1 (Arm S) vs. CAPOX (Arm C), as well as other relevant clinical variables such as comorbidity and completion of planned treatment. A total of 6602 patients were included in the analysis, with 4199 in Arm S and 2403 in Arm C. After propensity score matching, the final study population consisted of 2067 patients in each arm. Arm C showed statistically inferior 5-year overall survival (OS) and disease-free survival (DFS) rates compared to Arm S (84.0% vs. 90.0%; p < 0.0001; and 78.4% vs. 86.1%; p < 0.0001). Age (65 ≥ vs. < 65) and the incomplete planned treatment also had a significant negative effect on both OS and DFS. In the multivariable analysis, Arm C still showed worse OS (hazard ratio [HR], 1.609; 95% confidence intervals [CI], 1.339–1.934; p < 0.0001) and DFS (HR, 1.552; 95% CI 1.333–1.807; p < 0.0001) than Arm S. Both S-1 and CAPOX showed excellent efficacy, but this nationwide cohort study suggests that S-1 may be a better option in certain clinical situations.