Validation of changes in stage by the new N category in the 9th edition of lung cancer staging for resected non-small cell lung cancer

Introduction: The reclassification following N2 subcategorization (N2a vs. N2b) in the 9th edition of lung cancer staging has not yet been externally validated. This study aimed to evaluate and compare the survival outcomes of reclassified stages in patients with resected non-small cell lung cancer. Materials and methods: Patients who underwent lobectomy or pneumonectomy for non-small cell lung cancer between January 2015 and December 2021 were retrospectively analyzed. Overall survival (OS) comparison and risk stratification within the pathologic N category (pN0, 1, 2a, 2b), node-positive T1 tumors (T1N1, T1N2a, T1N2b), stage IIB tumors (T1N2a, T2N1, T3N0), and T2-3N2 tumors (stage IIIA, IIIB) were performed using the Kaplan-Meier method and multivariable Cox proportional hazards analysis. Results: A total of 3,864 patients were analyzed, including 962 patients with pathologically node-positive tumors. pN2a and pN2b tumors exhibited distinct survival (p<0.001). Survival separation between neighboring pT1N1-2b tumors was statistically marginal (p=0.06 and 0.09); however, clear separation was observed in clinical T1 tumors (p<0.05). pT1N2a tumors that were downstaged from stage IIIA to stage IIB showed comparable survival to other stage IIB tumors (vs. pT2N1 and pT3N0; p=0.79 and 0.35, respectively). In pT2-3 tumors (stage IIIA and IIIB), OS risk stratification between pN2a and pN2b tumors, except for between pT3N2a and pT2N2b, was valid (p<0.05). Conclusion: The reclassification of stages in the 9th edition of lung cancer staging based on N2 subcategorization is considered reasonable.