The IASLC Mesothelioma Staging Project: Proposals for the ‘N’ Descriptors in the Forthcoming 9th Edition of the TNM Classification for Pleural Mesothelioma

Introduction The International Association for the Study of Lung Cancer (IASLC) developed a global multicenter database to propose evidence-based revisions for the 9th edition of the Tumor Node Metastasis (TNM) classification of pleural mesothelioma (PM). This study analyses the M category to validate 8th edition M category recommendations. Methods Cases were submitted electronically or by transfer of existing institutional databases for patients with histologically or cytologically confirmed PM. The presence and number of metastases (single versus multiple) in each of eight organ systems were reported for patients with M1 disease at diagnosis. Overall survival (OS) was calculated by the Kaplan-Meier method. Differences in OS were assessed by log-rank test. Results Of 7,338 submitted cases, 3,598 were eligible 3,221 had sufficient data for clinical staging; 228 cases (7%) were M1. Median overall estimated survival was inferior for M1 compared with M0 patients: 10.5 versus 21.5 months, respectively (p<0.0001); estimated one-year survival was 46% versus 71%. OS differences between M categories were preserved within histologic subgroups. Among 158 patients with organ-specific documentation of M1 disease, there was no statistically significant difference in OS between those with intrathoracic versus more distant metastatic disease (14.4 months versus 10.9 months, p=0.64). No significant survival difference was detected between patients with metastatic disease in a single organ system versus multiple organ systems (12.6 versus 8.8 months, p=0.45). Conclusion This evidence-based analysis of the M category for PM conforms with the 8th edition M-descriptors. No changes are proposed in the 9th edition of the mesothelioma M category.