Prognostic effect of postoperative duration until adjuvant chemotherapy and cumulative S-1 dose in gastric cancer

<jats:title>Abstract</jats:title> <jats:p><jats:bold>Background</jats:bold>Adjuvant chemotherapy (AC) following curative gastrectomy for stage II/III gastric cancer (GC) is recommended in Japan. However, for various reasons, patients cannot always start AC at the appropriate time. This study was designed to investigate the effect of the postoperative duration until adjuvant chemotherapy (PDAC) and cumulative S-1 dose on prognosis.<jats:bold>Methods</jats:bold>Between 2008 and 2014, 76 consecutive GC patients who underwent postoperative S-1 monotherapy were enrolled in this study.<jats:bold>Results</jats:bold>Postoperative complications of Clavien–Dindo grade II or higher and postoperative peak C-reactive protein of 8 mg/dl or higher were significantly associated with delayed AC. The cut-off value of PDAC selected to most effectively stratify prognosis was 7 weeks. For relapse-free survival (RFS), patients with PDAC ≥ 7 weeks had an insignificantly poorer prognosis than those with PDAC < 7 weeks (<jats:italic>p</jats:italic> = 0.017, 5-year RFS: PDAC ≥ 7 weeks vs. PDAC < 7 weeks, 48.5% vs. 77.0%). A multivariate analysis showed that PDAC ≥ 7 weeks [<jats:italic>p</jats:italic> = 0.007; hazard ratio (HR) 3.99 (95% CI: 1.46–11.5)] and cumulative S-1 dose > 12,000 mg [<jats:italic>p</jats:italic> = 0.033; HR 0.38 (95% CI: 0.14–0.93)] were independent prognostic factors. In patients with a cumulative S-1 dose ≥ 12,000 mg, there were no prognostic differences between patients with and without PDAC ≥ 7 weeks.<jats:bold>Conclusions</jats:bold>7 weeks after surgery could be an indicator starting AC. A cumulative S-1 dose of more than 12,000 mg might be a key dose for diminishing the poor prognostic effects of delaying AC.</jats:p>