Insufficient examined lymph node count underestimates staging in pN3a patients after curative gastrectomy: a multicenter study with external validation

Purpose The present study aims to validate possible stage migration of lymph node metastasis related to the insufficient examined lymph node (ELN) count in pN3a gastric cancer (GC) patients. Methods 1976 pN3 patients who underwent the R0 surgery in three high-capacity institutions in China were enrolled to explore the stage migration of nodal involvement, and 3146 pN3 cases from the Surveillance, Epidemiology, and End Results (SEER) Program Registry were used as an external validation cohort. Results After the propensity score matching of the Chinese cohort, the ELN count, as an independent predictor for GC outcome, was confirmed to be associated with the stage migration of lymph node metastasis in pN3a patients based on the univariate and multivariate survival analyses. Logistic regress was adopted to elucidate that the ELN count was an independent factor related to the long-term survival status of GC patients after curative surgery. Likelihood ratio test showed that the ELN count had the smallest Bayesian information criterion value among the clinicopathologic variables, corresponding to an efficient model to predict outcomes. Subsequently, stage migration of lymph node metastasis was predominantly detected in pN3a patient sub-group with insufficient (less than 16) ELN count, who presented with similar prognosis as the pN3b patients ( P = 0.463) as per the stratum analysis with Kaplan–Meier. These methods were further validated using data from the SEER cohort, and the similar promising results were obtained. Conclusion pN3a patients with insufficient ELN count should be considered as pN3b cases to achieve accurate prognostic evaluation after curative gastrectomy.