# Validation of the 9th Edition of the TNM Classification in Patients with NSCLC and Lymph Node Involvement: A Retrospective, Multicentric, Observational Study

## TL;DR

This study validates the 9th edition of the TNM classification for NSCLC, showing improved staging accuracy, especially for stage IIIB patients with lymph node involvement.

## Contribution

The study provides empirical validation of the 9th edition TNM classification for NSCLC, highlighting its improved prognostic value and suggesting refinements for stage IIIB.

## Key findings

- Stages IIB and IIIA showed largely homogeneous prognostic behavior with limited subgroup differences.
- Stage IIIB demonstrated significant survival heterogeneity, with T4N2b having the poorest outcomes.
- The 9th edition TNM classification shows improved prognostic granularity compared to previous editions.

## Abstract

The ninth edition of the TNM classification introduced refinements in nodal staging for non-small-cell lung cancer (NSCLC), particularly the subdivision of mediastinal N2 disease into single-station (N2a) and multi-station (N2b) involvement, with corresponding changes in stage grouping. This multicenter retrospective study aimed to validate the prognostic performance of the new TNM system in surgically treated patients with nodal involvement. A total of 291 non-small-cell lung cancer (NSCLC) patients with pathologically proven N1 or N2 disease who underwent anatomical pulmonary resection between 2020 and 2023 were analyzed. Patients were reclassified according to the ninth TNM edition, and overall survival (OS) and disease-free survival (DFS) were evaluated. Stages IIB and IIIA showed largely homogeneous prognostic behavior, with limited differences among subgroups. In contrast, stage IIIB demonstrated significant survival heterogeneity, with the poorest outcomes observed in T4N2b disease. These findings support the improved prognostic value of the ninth TNM edition and suggest further refinement for stage IIIB.

Background: The ninth edition of the TNM classification introduced refinements in nodal staging, subdividing mediastinal N2 disease into N2a (single-station) and N2b (multi-station) involvement, alongside several stage group adjustments. The aim of this study is to validate the new TNM in patients with nodal involvement who underwent surgery. Methods: This is a multicentric, retrospective study including NSCLC patients with pathological N1 or N2 involvement who underwent anatomical pulmonary resection between January 2020 and December 2023. Clinical, surgical, and pathological data were collected, including tumor characteristics, lymphadenectomy details, and adjuvant therapy. Patients were reclassified according to the ninth TNM groups: stage IIB, including T1N1, T2N1, and T3N0; IIIA, including T1N2b, T2-3N2a, T3N1, T4N0, and T4N1; and IIIB, including T2-3N2b, T4N2a, and T4N2b. Overall survival (OS) and disease-free survival (DFS) were analyzed using Kaplan–Meier curves. Results: The final analysis involved 291 patients. The three- and five-year OS rates were 82% and 71% for stage IIB, and 75% and 58% for stage IIIA, respectively. At stage IIB, a significant difference was found only for DFS comparing T2N1 and T1N2a, whereas stage IIIA showed no significant differences in either OS or DFS, confirming its prognostic homogeneity. Conversely, stage IIIB exhibited significant heterogeneity in survival (OS p = 0.031; DFS p < 0.0001), with T4N2b subgroups showing the worst outcomes compared to T2-3N2b and T4N2a. Conclusions: Our validation of the ninth edition of lung cancer staging shows improved prognostic granularity: IIB shows non-homogeneous DFS, IIIA is homogeneous, and IIIB shows major OS/DFS substage differences, warranting analyses with larger samples for refined stratification.