The new TNM classification for lung cancer

The 2024 edition of ELCC featured the presentation of the new TNM classification for lung cancer. To discuss this 9^th edition of the TNM classification, Prof Dr Mariana Brandão, medical oncologist at the Jules Bordet Institute in Brussels was joined by Prof Dr Paul Van Schil, thoracic surgeon at the Antwerp University hospital and the current president of the International Association for the Study of Lung Cancer (IASLC).

With respect to the ‘T’, the 9^th edition of the TNM classification is similar to the 8^th edition, despite some discussion on a poorer prognosis for T3 patients with chest wall involvement compared to other T3s.

In terms of the ‘N’, the new classification has subdivided N2 patients into a N2A and N2B category. In this, N2A disease refers to the involvement of a single station, whereas multiple stations are involved in patients with N2B disease. As such, from a therapeutic point of view, most N2A cases will still be resectable, while N2B patients are initially no longer candidates for surgery and require a combined modality therapy.

Finally, for the ‘M’, the 9^th edition does not show any changes for the M1A and M1B categories. In contrast, M1C has been further divided into M1C1 and M1C2, respectively referring to patients with metastases in one organ system and patients with metastases in multiple organs.

Commenting on this new classification, Prof Van Schil indicated that there are also plans to develop a ‘TNM essentials’ classification that requires less complex evaluations making it easier to use in low-income countries. Likely these essential criteria will start with an evaluation of the M. If this indicates the presence of metastases, it is probably no longer necessary to perform a detailed TNM staging. Subsequently, the N is evaluated after which the T is only of clinical relevance in patients with N0 disease.

On a final note, Prof Van Schil addressed the updated TNM classification of thymic epithelial tumors. For these tumors, the only changes have been made in the ‘T’. In fact, the new classification makes a distinction between T1A and T1B thymic epithelial tumors, with a tumor size of 5cm as the discriminator between the two. Furthermore, mediastinal pleura will no longer be a factor to determine the ‘T’ in the new classification. Another change in the T classification of thymic epithelial tumors is that patients with invasion of the lung or the phrenic nerve have been downstaged from T3 to T2. For the N and M, no changes have been made in the classification of thymic epithelial tumors.