Favorable long-term outcomes of one-year adjuvant S-1 monotherapy for pathological stage II or III gastric cancer treated at a high-volume center

Background One-year adjuvant S-1 monotherapy following D2 gastrectomy has been the Japanese treatment standard for pathological stage II or III gastric cancer since the Adjuvant Chemotherapy Trial of S-1 for Gastric Cancer (ACTS-GC) was concluded in 2007. Trial patients were selected according to the 13th edition of the Japanese classification (JC-13). The JC-13 and the TNM classification underwent major revisions in 2010 (JC-14/TNM-7). However, neither the recent therapeutic results for patients with stage II/III disease defined by the current system nor comparisons with the ACTS-GC-results have been reported. Methods The 390 study patients had pathological stage II/III gastric cancer defined by the JC-14/TNM-7 and treated with S-1 following D2 gastrectomy between 2008 and 2012. The completion rate of 1-year S-1, first relapse site, and stage-specific survival according to the JC-14/TNM-7, JC-13, and TNM-6 were examined and the results compared with those of the ACTS-GC. Results The completion rate for 1-year S-1 (69.5%) was slightly higher than in the ACTS-GC. The recurrence pattern was almost identical. The 5-year overall survival rates of pathological IIA, IIB, IIIA, IIIB, and IIIC in the JC-14/TNM-7 were 96.0, 85.5, 81.8, 72.0, and 51.1%, respectively. Their 5-year overall and relapse-free survival rates by the JC-13 and TNM-6 systems were favorable as compared to those of ACTS-GC patients for all substages. Conclusions Survival outcome shown in this study of patients treated with 1-year adjuvant S-1 after D2 gastrectomy at a high-volume cancer hospital will provide a reference for future adjuvant trials targeting JC-14/TNM-7 stage II/III disease.