Compare S-1 for 9 Months to 1 Year as Adjuvant Chemotherapy in Stage II Gastric Cancer (SMAC）

It has been identified that S-1 is an effective adjuvant treatment for East Asian patients who have undergone a D2 dissection for locally advanced gastric cancer（GC) in the Japanese Adjuvant Chemotherapy Trial of TS-1（S-1) for Gastric Cancer (ACTS-GC) trail, And S-1 has become one of the standard therapies to these patients. But it is still unknown whether it would improve equally or even more to overall survival(OS) and disease-free survival(DFS) than S-1 for 1 year compared with S-1 for 9 months. As a result, An further clinical trial is still needed, This trial is designed to investigate the efficacy and safety of S-1 for 9 months versus S-1 for 1 year as adjuvant chemotherapy after D2 resection in patients with gastric cancer.

In this study, patients histologically confirmed stage II and who received D2 resection were randomly assigned to receive S-1 for 9 months or S-1 for 1 year. Patients aged from 18 to 75 years and adequate organ function are randomized 1:1 to S-1 for 9 months and S-1 for 1 year. Both are the 3-week recycle of S-1 (80-120mg per day) for 2 weeks, followed by 1 week of rest. The primary endpoint is 3-year DFS, and the secondary endpoint is 5-year OS and safety. Final study analysis will be conducted at the end of the 5th year after the last patient's enrollment. In summary, we hold the hypothesis that S-1 for 9 months is equally effective, safer, and easier to carry out. If possible, there will be a new adjuvant chemotherapy strategy for gastric cancer patients after D2 resection.

To ensure the quality of the study, two interim analyses will be planned at the half and the completion of the study respectively. The DATA and Safety Monitoring Committee will independently review the interim analysis and stop the study ahead of schedule if necessary. Furthermore, to improve the study progress and quality, the in-house interim monitoring will be performed.