Comparison Between Lymph Node Station- and Zone-Based Classification: An Extended Analysis With the Ninth Edition TNM...

The ninth edition of the TNM classification by the International Association for the Study of Lung Cancer subdivides pN2 disease into N2a and N2b based on the number of involved lymph node (LN) stations. This study compares the prognostic performance of station-based versus zone-based LN classification in surgically resected NSCLC.

We retrospectively analyzed 11,047 patients who underwent curative resection with systematic LN dissection for NSCLC between 2005 and 2022. In the zone-based system, LN stations were grouped into broader anatomical regions: peripheral or hilar zones for N1 node and upper mediastinal, lower mediastinal, aortopulmonary, and subcarinal zones for N2 nodes. Patients were classified as N2a or N2b based on single- versus multi-zone or station involvement. Overall survival (OS) and freedom from recurrence (FFR) were evaluated using Kaplan-Meier analysis and Cox regression. Prognostic performance was compared using Harrell's C-index, Akaike Information Criterion, and R ².

Both classification systems significantly stratified OS and FFR (p < 0.001). Zone-based classification revealed clearer separation between N2a and N2b groups, particularly in OS (5-y OS: 55.6% versus 37.2%). Multivariable analysis confirmed both systems as independent prognostic factors, with zone-based N2b revealing the highest hazard ratios. Model fit was slightly better with zone-based classification. Notably, 28.8% of patients with station-based N2b were reclassified as zone-based N2a, revealing prognostic heterogeneity.

Zone-based LN classification improves prognostic discrimination compared with station-based grouping and may complement future refinements of the TNM nodal staging system.

Institutional Review Board of Asan Medical Center (2024-1351).