Implementation of the 9th TNM for lung cancer: practical insights for radiologists

Lung cancer is the most common and deadly cancer worldwide. The 9th edition of the tumor node meta (TNM) classification system, effective from January 1, 2025, introduces significant updates. Notably, the N2 category is newly divided into N2a (single-station involvement) and N2b (multiple-station involvement), which reflects distinct prognostic implications. Additionally, the M1c category is now subcategorized into M1c1 (multiple metastases in a single organ system) and M1c2 (metastases in multiple organ systems), affecting stage classification. This reclassification allows for potential downstaging, which could expand treatment options for affected patients. Accurate imaging remains crucial for the classification of anatomical stages. As the TNM system evolves, enhanced imaging precision will play a key role in implementing these updates and ultimately improve patient outcomes. KEY POINTS: Question The 9th TNM for lung cancer introduces changes in the N2 and M1c descriptors, to better align with new therapeutic options and outcome studies. Findings Proper knowledge of the key changes of the 9th TNM can help radiologists offer clinicians a meaningful report. Clinical relevance Radiologists should incorporate the 9th TNM classification into their reports and discussions in multidisciplinary meetings, thus ensuring a common language across disciplines to enable clearer communication with other specialists, supporting more precise and cohesive decision-making in patient care.