The IASLC Lung Cancer Staging Project: Proposals for Revision of the M Descriptors in the Forthcoming (Seventh) Edition of the TNM Classification of Lung Cancer

Abstract

To analyze all nonlymphatic metastatic components (T4 and M1) of the current TNM system of lung cancer, with the objective of providing suggestions for the next edition of the TNM classification for lung cancer. Data on 100,809 patients were submitted to the International Association for the Study of Lung Cancer International Database. Of these, 5592 selected T4M0 and M1 patients fulfilled the inclusion criteria for the analysis. Specific categories of clinically staged T4 (lesions not continuous with the primary tumor) and M1 cases were compared with respect to overall survival using Kaplan-Meier survival estimates and comparisons via Cox regression analysis. Relevant findings were validated internally by geographic area and type of database and were validated externally by the North American Surveillance, Epidemiology and End Results Registries. Median survival for cT4M0 with malignant pleural effusion was significantly worse than that of other cT4M0 patients (8 months versus 13 months) and was more comparable with M1 cases with metastases to the contralateral lung only (10 months). M1 cases with metastases outside the lung/pleura had a significantly poorer prognosis than those with metastases confined to the lung, with a median survival of 6 months. Revisions to the TNM classification system for lung cancer should include grouping cases with malignant pleural effusions and cases with nodules in the contralateral lung in the M1a category, and cases with distant metastases should be designated M1b. In addition, cases with nodule(s) in the ipsilateral lung (nonprimary lobe), currently staged M1, should be reclassified as T4M0, in accordance with the recommendations of the T descriptor subcommittee of the IASLC international staging committee.