Effects of Continuing Adjuvant S-1 for 1 Year on the Prognosis of Gastric Cancer Patients: Results from a Prospective Single Center Study

Purpose: Although several clinical trials have proven the efficacy of adjuvant S-1 treatment in gastric cancers, it is still unclear which patients receive the most benefit. In this study, we prospectively recruited patients with locally advanced gastric cancer who had undergone curative resection followed by adjuvant S-1 administration to investigate which factors affect the outcomes. Materials and Methods: Between July 2010 and October 2011, we enrolled 49 patients who underwent curative resection for stage II or III gastric cancer and who subsequently received adjuvant S-1 treatment for 1 year. Results: Twenty-nine patients (59.2%) continued S-1 treatment for 1 year, and 12 patients (24.5%) experienced recurrent disease during the follow-up period. Patients with continuation of S-1 for 1 year had significantly increased rates of disease-free survival (P<0.001) and overall survival (P=0.001) relative to the patients who discontinued S-1 during year 1. Multivariate analysis indicated poor outcomes for patients with stage III disease and those who discontinued S-1 treatment. Excluding patients who discontinued S-1 due to cancer progression (n=7), adjuvant treatment with S-1 still demonstrated a significant difference in the disease-free survival rate between the patients who continued treatment and those who discontinued it (P=0.020). Conclusions: S-1 is tolerated as adjuvant treatment in gastric cancer patients. However, discontinuing S-1 treatment may be an unfavorable factor in the prevention of recurrence. S-1 adjuvant treatment should be continued for 1 year if possible through the proper management of toxicities.