As lung cancer treatments and screening protocols rapidly evolve, there is an ongoing need to ensure the system for staging tumors reflects the most up-to-date evidence possible for accurate diagnoses.
To that end, in 2024, the International Association for the Study of Lung Cancer (IASLC) recommended several significant updates to the tumor, node, metastasis (TNM) classification system for lung cancer, thymic tumors, and mesothelioma. The ninth edition of the TNM classification system—expected to be formally adopted by the American Joint Committee on Cancer and the Union for International Cancer Control in the coming months—includes updates to both the node (N) and metastasis (M) categories.
Executive Editor of the IASLC Staging Manual in Thoracic Oncology, Hisao Asamura, MD, said one of the more significant changes is the subdivision of the N2 category.
In the updated classification system, the N2 category is subdivided into N2a, which indicates metastasis confined to a single ipsilateral mediastinal or subcarinal station, and N2b, which refers to metastases in multiple mediastinal or subcarinal stations.
“N2a is single N2 station involvement, while N2b is multiple N2 station involvement. This is only one change, but it is a significant one,” said Dr. Asamura, who is Professor of Surgery and Chief of the Division of Thoracic Surgery at Keio University School of Medicine, Tokyo.
Lucia Viola, MD, an interventional pulmonologist at the Luis Carlos Sarmiento Angulo Cancer Treatment and Research Center and Colombian Pulmonology Foundation, Bogotá, Colombia, agreed the change is significant. However, she also expressed concerns about the education and training in endobronchial ultrasound (EBUS) which may be required in some parts of the world to properly implement this change.
“It may be difficult for some institutions to do a high-quality or optimal EBUS if they are not trained in the area,” Dr. Viola said. “Some of institutions have interventional pulmonologists—and very good ones—but they may know little about the changes in TNM.”
Additionally, compared with the eighth edition’s pathologic N category (pN1), the ninth edition’s pN2a and pN2b demonstrate a significant survival advantage when validated, he said. This change helps clinicians differentiate between single-station and multistation or subcarinal lymph node involvement, thereby helping improve the accuracy of prognosis predictions.
Further subdivision is also seen in the M category for the ninth edition. The M1c category has been divided into M1c1 (multiple extrathoracic metastases within a single organ system) and M1c2 (multiple extrathoracic metastases across several organ systems).
There are not any changes to the tumor (T) category; however, staging group changes are recommended in the ninth edition. T1N2a tumors have been reassigned to stage IIB, T2N2b to stage IIIB, and T2N2a to stage IIIA. Additionally, T1N1 has been downstaged from stage IIB to stage IIA.
“All of these changes are critically related to the choice of treatment,” Dr. Asamura said. “New treatment challenges will be based on the new classifications, which define the tumor burden more precisely than before.”
As is the case with most advances in health care, the adoption of the ninth edition is not the end of the evolution of the TNM classification system. Dr. Asamura said the IASLC is already actively working on the 10th edition, which will present additional challenges.
“The publication of the ninth edition staging criteria in 2024 is not the end of our task. We must consider the possibility of incorporating novel molecular factors into the TNM anatomic classifications,” he said. “If we incorporate additional factors, the TNM combinations will become considerably more complex, which is something we must consider.”