Efficacy and feasibility of S-1 plus oxaliplatin (C-SOX) for treating patients with stage III colon cancer (KSCC1303): final analysis of 3-year disease-free survival

Background: Adjuvant chemotherapy is an accepted treatment to improve survival rates in patients with stage III colon cancer, and regimens including oxaliplatin have been shown to be superior to those containing 5-FU alone. The purpose of this study was to examine the efficacy and feasibility of S-1 plus oxaliplatin (C-SOX) as adjuvant chemotherapy for patients with stage III colon cancer following curative resection. Methods: Patients with colon cancer who underwent curative resection were enrolled and received oral S-1 40–60 mg twice daily on days 1–14 every 3 weeks plus intravenous oxaliplatin 130 mg/m² on day 1 for eight courses. The primary endpoint was 3-year disease-free survival rate. Secondary endpoints were the rate of treatment completion, adverse events, relative dose intensity, and overall survival. Results: Between February 2014 and December 2014, 89 patients were enrolled. One patient was excluded from the analysis because of ineligibility, and the remaining 88 patients were included. The rate of protocol treatment completion was 72.3%. The relative dose intensity of S-1 and oxaliplatin was 72% and 76.3%, respectively. Hematological severe adverse events (Grade 3/4) were neutropenia (21.3%) and thrombocytopenia (15.7%). The most frequent symptom was diarrhea (Grade 3/4: 5.6%). The incidence of grade 2 neuropathy has decreased from 8.1 to 2.7% after 3 years of the therapy. Three-year disease-free survival rate was 73.9% (95% CI 63.8–81.9), and 3-year overall survival rate was 94.3% (95% CI 86.8–97.6) Conclusions: C-SOX is a safe and feasible adjuvant chemotherapy regimen in patients with stage III colon cancer undergoing curative resection.