TNM 9: what changed in lung cancer staging

The International Association for the Study of Lung Cancer revises the lung TNM classification roughly every eight years from a purpose-built international database; for the ninth edition it collected 124,581 patients diagnosed between 2011 and 2019 and analysed 76,518 of them. The T subcommittee tested the eighth-edition descriptors and recommended no change, so T is identical between the two editions. N changed: N2 is subdivided into N2a, involvement of a single ipsilateral mediastinal or subcarinal station, and N2b, involvement of multiple ipsilateral mediastinal stations with or without the subcarinal station. M changed at the far end: M1a and M1b are validated unchanged, while M1c is subdivided into M1c1, several metastases within one extrathoracic organ system, and M1c2, several metastases across organ systems, both remaining in stage group IVB. The stage groups were rebuilt to follow the new N and M categories: T1N1 moves to IIA, T1N2a to IIB, T3N2a to IIIA, and T2aN2b and T2bN2b to IIIB. The edition came into force on 1 January 2025. Two practical consequences: a systematic nodal staging that records which stations are involved, rather than a single positive sample, is now needed to assign N; and survival series that span the change cannot be pooled without restaging, because the same disease carries different labels either side of it. NICE NG122 still states that its recommendations were developed with the 7th edition of the AJCC staging system.