Delay in initiation of postoperative adjuvant chemotherapy with S-1 monotherapy and prognosis for gastric cancer patients: analysis of a multi-institutional dataset.

Abstract

This study aimed to evaluate whether the timing of initiating postoperative chemotherapy with S-1 monotherapy affects gastric cancer patients' prognosis. A multi-institution dataset identified patients with pStage II or III gastric cancer who received S-1 monotherapy for over 6months after curative resection between 2010 and 2014. Patients were divided into three groups based on the timing of S-1 monotherapy initiation. Prognostic factors for relapse-free survival (RFS) were investigated. We classified 401 patients into groups as follows: S-1 administered within 6weeks (n = 247), between 6 and 8weeks (n = 95), and after 8weeks (n = 59). The RFS times were not significantly different in the within 6weeks group and the between 6 and 8weeks group, but the after 8weeks group had a shorter RFS time compared with the other two groups (within 6weeks group vs. after 8weeks group; P = 0.0044). By disease stage, this trend was the same. The multivariable analysis showed that a larger tumor size (≥ 50mm), pStage III, and the after 8weeks group were independent prognostic factors for RFS (after 8weeks group: hazard ratio, 2.05; P = 0.0069). The prevalence of hematogenous metastasis as the initial recurrence site increased by delayed initiation of S-1. A forest plot revealed that delayed administration after 8weeks was associated with a greater risk of recurrence in most subgroups. Postoperative chemotherapy with S-1 monotherapy for gastric cancer is recommended to begin within 8weeks after surgery.