The International Association for the Study of Lung Cancer (IASLC) recently introduced the ninth edition of the TNM classification for lung cancer. This milestone is supported by a comprehensive database comprising 124 581 lung cancer patients from 75 centers across 25 nations between 2011 and 2019. Following the exclusion of incomplete data, the analysis focused on 87 043 patients. These insights guided the modifications in the ninth edition of the TNM classification for lung cancer. The updated classification now includes a higher representation of Asian patients, particularly showing significant growth among Chinese patients. This revised classification will offer more pertinent benchmarks for the diagnosis and prognostic assessment of lung cancer. This article delves into the database updates, stage adjustments, and rationale behind the IASLC ninth edition of the TNM classification for lung cancer.