Out with the old - advancements and shortcomings of the updated 9th edition of the Tumor, Node, Metastasis (TNM) classification system for lung cancer.

Objectives: The 9th edition of the Tumor, Node, Metastasis (TNM-9) lung cancer classification is set to replace the 8th edition (TNM-8) starting in 2025. Key updates include the splitting of the mediastinal nodal category N2 into single- and multiple-station involvement, as well as the classification of multiple extrathoracic metastatic lesions as involving a single organ system (M1c1) or multiple organ systems (M1c2). This study aimed to assess how the TNM-9 revisions affect the final staging of lung cancer patients and how these changes correlate with overall survival (OS).

Methods: This retrospective cohort study included patients diagnosed with lung cancer between 2018 and 2021, who were staged according to both TNM-8 and TNM-9 criteria. The staging classifications were analyzed and compared in relation to OS.

Results: Among a total of 914 patients, 42 were re-staged using TNM-9. Of the 382 patients classified as stage IVB, 55.9% were reclassified as M1c2. Despite an absolute increase in mean OS for patients re-staged from IIB to IIA and from IIIA to IIB, the observed differences were not statistically significant. Median OS differed significantly both within stage IVB and between patients with M1c2 disease and other stage IV subgroups. Multi-organ metastatic disease was an independent predictor of poorer OS, regardless of age, sex, performance status, and oncologic treatment.

Conclusions: TNM-9 improves prognostic accuracy in lung cancer. Although patients with multiple extrathoracic metastases involving different organ systems are not yet independently staged from IVB, they demonstrated significantly poorer OS compared to other advanced-stage patients.