Time to initiation or duration of S-1 adjuvant chemotherapy; which really impacts on survival in stage II and III gastric cancer?

Background: Surgical resection with S-1 adjuvant chemotherapy (AC) is the standard of care for stage II–III gastric cancer (GC). However, it is unclear if time to initiation and duration of S-1 AC impact on survival. Methods: A multi-institutional GC database identified 498 patients who were treated with S-1 AC after D2 or more extended radical surgery for stage II–III gastric cancer. Patients were divided into four groups according to the interval between surgery and initiation of AC and the duration of AC as follows: group A (n = 226), who received AC earlier (≤6 weeks) and for longer (≥6 months) after surgery; group B (n = 160), who received AC later (>6 weeks) and for longer after surgery; group C (n = 46), who received AC earlier but for a shorter period (<6 months) after surgery; and group D (n = 66), who received AC later and for a shorter period after surgery. Prognostic factors for overall survival (OS) were investigated using multivariate analysis. Results: The 5-year OS was 69.5%. Pathological stage II disease (hazard ratio (HR), 0.334; 95% confidence interval (CI), 0.215–0.499), with an OS of 85.8% versus 60.5% for stage III disease, as well as a longer duration (≥6 months) of S-1 (HR, 0.498; 95% CI, 0.355–0.706), with an OS of 74.3% versus 53.0% for a shorter duration (<6 months) of S-1, were identified as significant prognostic factors for long-term survival. Time to initiation was not associated with OS. Conclusions: A duration of S-1 AC of ≥6 months, but not time to initiation within 6 weeks, impacts on OS in stage II–III gastric cancer.