Validation Study for the N Descriptor of the Newly Proposed Ninth Edition of the TNM Staging System Proposed by the International Association for the Study of Lung Cancer

Introduction The aim of this study was to validate the discriminatory ability and clinical utility of the N descriptor of the newly proposed 9th edition of the TNM staging system for lung cancer in a large independent cohort. Methods We retrospectively analyzed patients who underwent curative surgery for non-small cell lung cancer (NSCLC) between January 2004 and December 2019. The N descriptor of patients included in this study was retrospectively reclassified based on the 9th edition of the TNM classification. Survival analysis was performed using the log-rank test and Cox proportional hazard model to compare adjacent N categories. Results A total of 6649 patients were included in this study. The median follow-up period was 54 months. According to the newly proposed 9th edition N classification, 5573 (83.8%), 639 (9.6%), 268 (4.0%), and 169 (2.5%) patients were classified into the clinical N0, N1, N2a, and N2b categories and 4957 (74.6%), 744 (11.2%), 567 (8.5%), and 381 (5.7%) were classified into the pathologic N0, N1, N2a, and N2b categories, respectively. The prognostic differences between all adjacent clinical and pathologic N categories were highly significant in terms of both overall survival (OS) and recurrence-free survival (RFS). Conclusions We validated the clinical utility of the newly proposed 9th edition N classification for both clinical and pathologic stages in NSCLC. The new N classification showed clear prognostic separation between all categories (N0, N1, N2a, and N2b) in terms of both OS and RFS.