Abstract:Background and Aims Tumor deposits (TDs) may influence prognosis beyond the current 8th edition AJCC pTNM nodal classification in gastric cancer (GC). This study investigates the prognostic value of TD number and proposes an improved pN staging (mpN) that classifies patients with TD number >1 as pN3b. We validated the mpN staging against the 8th AJCC pN staging.Methods A dual-center retrospective cohort study was performed, including 1 327 patients who underwent radical gastrectomy at Sun Yat-sen University Cancer Center (2011-2015; test cohort) and 340 patients from Guangdong Provincial People's Hospital (2015-2022; validation cohort). Patients were dichotomized into low-TD (≤1) and high-TD (>1) groups. Outcomes were overall survival (OS) and disease-free survival (DFS). Survival analyses used Kaplan-Meier curves, IPTW, and Cox regression. Predictive performance of staging systems was assessed by time-dependent ROC (tROC)/tAUC, concordance index (C-index) and Akaike information criterion (AIC).Results TDs were present in 435/1 327 (32.7%) in the test cohort. Presence of TD was associated with worse OS (IPTW-adjusted HR=2.69, 95% CI=2.18-3.31, P<0.01) and DFS (HR=2.82, 95% CI=2.32-3.42, P<0.01). In multivariable models, TD remained an independent adverse factor for OS (HR=1.65, 95% CI=1.34-2.05; P<0.01) and DFS (HR=1.74, 95% CI=1.43-2.11, P<0.01). Increasing TD number correlated with progressively poorer survival; X-tile identified >1 as an optimal cutoff, with high-TD patients showing markedly worse outcomes (OS: adjusted HR=3.65, 95% CI=2.74-4.88; DFS: adjusted HR=3.74, 95% CI=2.85-4.91; both P<0.01). Incorporation of TD number into the mpN staging (assigning TD>1 to pN3b) improved prognostic discrimination: in the test cohort 5-year OS tAUC was 0.746 for mpN vs. 0.703 for AJCC pN (C-index 0.738 vs. 0.721, AIC 5 805.27 vs. 5 849.30); similar improvements were observed in the validation cohort.Conclusion TD presence and number exert significant negative prognostic impact in GC. Classifying patients with TD number >1 as pN3b enhances prognostic accuracy. Routine reporting of TD counts and further prospective multicenter validation of mpN staging are warranted.