Update: The New 9th Edition TNM Classification for Lung Cancer Is Now in Use.

Abstract

Lung cancer is the leading cause of cancer-related mortality worldwide. Among the parameters determining prognosis in lung cancer, the stage of the disease holds primary importance. Staging provides a universally accepted terminology for describing the anatomical characteristics of cancer, facilitating reliable communication in clinical research, evaluation of treatment outcomes, and prognosis. The tumor, node, metastasis (TNM) staging system, developed by the American Joint Committee on Cancer (AJCC) and the International Union for Cancer Control (UICC), serves as a simple, practical, and globally recognised staging framework. Over the past two decades, the International Association for the Study of Lung Cancer has been conducting a global three-phase project aimed at revising the TNM classification. The first two phases of this project were focused on revising the 7th and 8th editions of the lung cancer TNM staging under the guidance of AJCC and the UICC. The third and final phase, the 9^th staging project, will be completed and will be implemented as of January 1, 2025. This review aims to examine the 9^th version of the TNM staging system compared to previous versions, and evaluate the structural modifications, statistical foundations, and clinical implications of the new system. In the study, current data regarding the 9^th version of the TNM staging system have been analysed, the revisions made to the T, N, and M components are detailed, and the fundamental changes between the 8^th and 9^th versions are compared using tables. Furthermore, the effects of the staging system on daily clinical practice are discussed.