Cumulative total S-1 dose in adjuvant chemotherapy affects the long-term outcome following curative gastrectomy for gastric cancer

A recent JCOG1104, OPAS-1 trial revealed the significance of S-1 duration. However, the significance of cumulative total S-1 dose (CTSD) remains unclear. In this study, we designed to evaluate the prognostic effect of CTSD on adjuvant chemotherapy after curative gastrectomy. We retrospectively analyzed 77 consecutive pStage II and III gastric cancer (GC) patients, who underwent curative gastrectomy followed by adjuvant S-1 chemotherapy from 2008 through 2014. CTSD of 20000 mg was the upper-limit of cut-off value to stratify the prognosis (5-year relapse free survival (RFS); CTSD < 20000 mg vs. CTSD ≥ 20000 mg: 51.9% vs. 85.1%, P = 0.004). Compared patients with CTSD more than 20000 mg, those with CTSD less than 20000 mg had a significantly higher rate of preoperative anemia (P = 0.041), low nutrition (P = 0.008) and open gastrectomy (P = 0.012). Multivariate Cox’s proportional hazards model for RFS proved that CTSD less than 20000 mg was an independent prognostic factor [P = 0.031, HR 3.32 (95% CI: 1.11-11.1)] although S-1 intensity and duration were not independent prognostic factors. The cumulative total S-1 dose more than 20000 mg might contribute to better prognosis.