Treatment using oxaliplatin and S-1 adjuvant chemotherapy for pathological stage III gastric cancer: a multicenter phase II study (TOSA trial) protocol

Background: Recent studies demonstrated the efficacy of S-1-based adjuvant chemotherapy administered for six months after curative surgery for stage III gastric cancer; however, it is unproven whether this type of combination chemotherapy is more effective than the standard adjuvant chemotherapy of S-1 for one year. Methods: This multicenter phase II study evaluate the efficacy and safety of adjuvant chemotherapy using S-1 plus oxaliplatin followed by S-1 for up to one year for curatively resected stage III gastric cancer in patients aged over 20 years. Treatment initially comprises oral fluoropyrimidine S-1 (80 mg/m(2)) administered twice daily for the first 2 weeks of a 3-week cycle. On day 1 of a second 3-week cycle, patients will receive 100 mg/m(2) of intravenous oxaliplatin followed by 80 mg/m(2) of S-1 (maximum 8 cycles). Then, the patients will receive 80 mg/m(2) of S-1 daily for 4 weeks, followed by 2 weeks of no chemotherapy. This 6-week cycle will be repeated during the first year after surgery. The primary endpoint is relapse-free survival for 3 years and secondary endpoints are safety, including the incidence of adverse events, and grading of neuropathy with each treatment cycle. The planned sample size of 75 patients is appropriate for this trial. The data will be analyzed on an intention-to-treat basis, assuming a two-sided test with a 5% level of significance. Discussion: In contrast to previous trials, the current study involves administration of S-1 until one year after surgery in addition to prior S-1 plus oxaliplatin, and is the first study to evaluate the safety and efficacy of S-1 plus oxaliplatin followed by S-1 for up to one year in patients with curatively resected stage III gastric cancer.