Association between adjuvant component of perioperative chemotherapy and survival outcomes in resected gastric cancer (GC).

378 Background: Perioperative chemotherapy is the standard of care for resectable GC but many patients do not proceed to or complete adjuvant chemotherapy (AC). It remains unclear whether AC following neoadjuvant chemotherapy (NAC) improves survival. Methods: Patients with GC who received NAC and underwent curative-intent gastrectomy from 2006-2022 were identified from an institutional database. Patients with mismatch repair-deficient/microsatellite instability-high tumors, GEJ tumors, M1 disease, neoadjuvant radiotherapy, total neoadjuvant intent treatment, incomplete NAC (<66% of planned cycles), and incomplete data were excluded. A lymph node ratio (LNR) risk cutoff was determined using maximally selected rank statistics. Kaplan-Meier analysis with log-rank tests were used to compare overall survival (OS) and disease-free survival (DFS). Cox proportional hazards regression models were used to identify independent predictors of OS and DFS. All analyses were performed in R statistical software. Results: Of 340 patients included, 264 (78%) received AC. Most common reasons for incomplete AC were postoperative complications (20%), poor performance status (16%), minimal pathologic response to NAC (14%), patient choice (14%), and NAC toxicity (9%). Median follow-up was 6.4 years. In the overall cohort, there was no significant difference in OS (median 10 vs. 8.3 years; p=0.14) or DFS (7.0 vs. 7.5 years; p=0.12) between AC and non-AC groups. In node-negative (ypN-) patients (n=170), there was no association between receipt of AC and OS (12 vs. 10 years; p=0.6) or DFS (12 vs. 10 years; p=0.8). On univariable analysis, lack of AC receipt was not associated with shorter OS (p=0.3) or DFS (p=0.4). In the node-positive (ypN+) cohort (n=170), AC receipt was associated with significantly longer DFS (4.8 vs. 2.7 years; p=0.031) but not OS (5.5 vs. 2.8 years; p=0.071). However, on multivariate analysis, AC only showed a non-significant trend towards longer DFS (HR 0.77 [95% CI 0.49-1.19]; p=0.20). High-risk patients based on LNR (LNR>0.0684; n=112) who received AC (n=87; 78%) had longer OS (p=0.033) and DFS (p=0.014). No such differences were observed in the low risk LNR subgroup (LNR<0.0684; n=227). Conclusions: Following NAC, AC was not associated with improved survival in patients with ypN- GC. The association between AC and survival in ypN+ GC remains unclear but LNR may be used to identify patients with ypN+ disease who may benefit from AC. These observations require prospective validation but may have implications for clinical care and future trial design.