Background: S-1 adjuvant chemotherapy is commonly administered postoperatively for stage II and III advanced gastric cancer.
Methods: This study included 113 patients treated with S-1 adjuvant chemotherapy after surgery for stage II and III advanced gastric cancer. These patients were divided into 4 groups: group A (n = 63), who had a longer duration (≥6 months) and earlier S-1 administration (≤6 weeks) after surgery; group B (n = 16), who had a longer and later S-1 administration (>6 weeks) after surgery; group C (n = 27), who had a shorter duration (<6 months) and earlier S-1 administration after surgery; and group D (n = 7), who had a shorter and later S-1 administration after surgery.
Results: The recurrence rates in groups A, B, C, and D were 15.7, 43.8, 44.4, and 57.1 %, respectively (A vs. B, p < 0.05, A vs. C and D, p < 0.01). The survival time of group A was significantly longer than that of other groups (p < 0.005). In addition, the survival time of patients with severe complications was significantly shorter than that of patients with non-severe complications (p < 0.05). An earlier S-1 administration after surgery was the only independent prognostic factor in the multivariate analysis.
Conclusions: The prognosis of advanced gastric cancer was significantly related to the start of S-1 adjuvant treatment within 6 weeks after surgery.