Analysis of outcomes according to start timing of adjuvant chemotherapy in patients with gastric cancer: a retrospective nationwide cohort study.

Background: Gastrectomy with D2 lymph node dissection followed by adjuvant chemotherapy (AC) with S-1 or capecitabine/oxaliplatin (CAPOX) is the standard treatment for stage II and III gastric cancer (GC). However, there is no established guideline for the start timing of AC.

Methods: We analyzed data from the Korean Health Insurance Review and Assessment Service on 19 140 GC patients who received AC with S-1 (n = 10 442) or CAPOX (n = 8698) between January 2014 and December 2018. Patients were categorized based on AC initiation timing: within 6 weeks (n = 12 843), 6-8 weeks (n = 5386), and >8-16 weeks (n = 911).

Results: Initiating AC within 6 weeks significantly improved 5-year disease-free survival (DFS) and overall survival (OS) compared to later initiation, with consistent findings across both S-1 and CAPOX groups (all P < .005). These associations remained significant in multivariable analysis and after propensity score matching (all P < .0001). However, this nationwide big-data analysis has limitations, including potential survival status misclassification and the absence of some important variables such as pathologic stage, performance status, and postoperative complications.

Conclusion: To optimize outcomes, AC for GC should be initiated within 6 weeks after gastrectomy, provided patients have fully recovered.