Validation of IASLC 9th Edition TNM Classification for Lung Cancer: Focus on N Descriptor

Abstract

Background: We externally validated the proposed 9^th edition of the TNM staging classification with our institution's prospectively collected data and compared it to the 8^th edition for overall survival (OS) and freedom from recurrence (FFR). Methods: A retrospective analysis was conducted of 3,711 cases of stage I-III non-small cell lung cancer that underwent surgical treatment from January 2004 to December 2020. Survival was compared using Kaplan-Meier curves and multivariable Cox regression analysis. The concordance index (C-index), Alkaike information criterion (AIC), and R² were used to assess the discriminatory ability. Results: In the 9^th edition, the N2 category (n = 347) was subdivided into N2a (n = 252, 72.6%) and N2b (n = 95, 27.4%). The TNM stage changes were as follows: 1) IIB to IIA, 140 cases (24.9%); 2) IIIA to IIB, 51 cases (11.4%); 3) IIIB to IIIA, 57 cases (59.4%); 4) IIIA to IIIB, 55 cases (12.5%). The survival curves of the proposed 9^th edition demonstrated similar patterns to those of the 8^th edition, but with a greater discriminative ability for OS and FFR. Subdividing N2 into N2a and N2b refined prognosis prediction. The C-index, AIC, and R2 demonstrated improved values in the proposed 9th edition compared to the 8^th edition. Conclusions: The proposed 9^th edition of the TNM staging classification for lung cancer showed favorable prognostic validity and better discrimination ability than the 8^th edition.