The IASLC Lung Cancer Staging Project: Proposals for Revision of the TNM Stage Groups in the Forthcoming (Ninth) Edition of the TNM Classification for Lung Cancer

Introduction The tumor, node and metastasis (TNM) classification of lung cancer is periodically revised. The International Association for the Study of Lung Cancer collected and analyzed a new database to inform the forthcoming 9th edition of the TNM classification. The results are herewith presented. Methods After exclusions, 76,518 patients from a total of 124,581 registered patients, were available for analyses: 58,193 with clinical stage, 39,192 with pathologic stage, and 62,611 with best stage non-small cell lung cancers. The proposed new N2 subcategories (N2a, involvement of single ipsilateral mediastinal or subcarinal nodal station; and N2b, involvement of multiple ipsilateral mediastinal / subcarinal nodal stations), and the new M1c subcategories (M1c1, multiple extrathoracic metastases in one organ system; and M1c2, multiple extrathoracic metastases in several organ systems) were considered in the survival analyses. Several potential stage groupings were evaluated, using multiple analyses, including recursive partitioning, assessment of homogeneity within and discrimination between potential groups, clinical and statistical significance of survival differences, multivariable regression and broad assessment of generalizability. Results T1N1, T1N2a and T3N2a subgroups are assigned to IIA, IIB and IIIA stage groups, respectively. T2aN2b and T2bN2b subgroups are assigned to IIIB. M1c1 and M1c2 remain in stage group IVB. Analyses demonstrate consistent ordering, discrimination of prognosis and broad generalizability of the proposed 9th edition stage classification of lung cancer. Conclusion The proposed stages for the 9th edition TNM improve the granularity of nomenclature about anatomic extent that has benefits as treatment approaches become increasingly differentiated and complex.