Background: In this study, we aimed to evaluate the effects of the transition from the 6^th edition of the Tumor, Node, Metastasis (TNM) staging system to the 7^th edition, and from the 7^th edition to the 8^th edition by comparing the stage migrations. We also aimed to externally validate the 8^th edition of the TNM staging system.

Methods: Between September 2005 and June 2015, a total of 1,077 patients (986 males, 91 females; mean age: 59.6±8.3 years; range, 35 to 84 years) with non-small cell lung cancer who underwent lung resection were retrospectively analyzed. We re-staged patients according to 6^th, 7^th, and 8^th TNM staging and compared the stage migrations of cases among the three staging systems.

Results: Stage migration in the transition to the 7^th edition of the TNM staging system was observed in 368 (34.1%) patients whereas it was observed in 541 (50.2%) patients in the transition to the 8^th edition (p<0.001). The rate of upstaging in transition to the 7^th edition staging system was 50.2% (n=185), whereas it was 98.1% (n=531) for the transition to the 8^th edition (p<0.001). The survival rates of Stages 1B, 2B and 3A increased with transition to the 7^th edition and the survival rates of Stages 1B, 2A, 2B, 3A, and 3B increased with the transition to the 8^th edition. The best stratification in the survival curves in the 6th edition was between 1B-1A and 3B-3A. In the 7^th edition, it occurred between 1B-1A, 3A-2B and 3B-3A and, in the 8^th edition, between 1B-1A and 3B-3A.

Conclusion: Stratification according to the 7^th edition showed better prognostic validity compared to the 6^th edition; and that of the 8^th edition was better compared to the 7^th edition.

Keywords : 8^th edition of TNM, external validation, non-small cell lung cancer, TNM classification