Study objective: Investigation of the behavior and treatment of diffuse malignant pleural mesothelioma (MPM) is hindered by the lack of an accurate universally accepted staging system. To address this problem, the International Mesothelioma Interest Group (IMIG) has developed a new TNM-based staging system.
Methods: The staging system was developed at a consensus meeting of IMIG members involved in clinical research in MPM, including the originators of previously proposed staging systems. The new staging system is based on the analysis of emerging information about the impact of T and N status on survival.
Results: In contrast to five previous staging systems, the T descriptors designated as T1, T2, T3, and T4, provide precise anatomic definitions of the local extent of the primary tumor. The N descriptors, designated as N0, N1, N2, and N3, are virtually identical to those used in the International Lung Cancer Staging System. The stage groupings recognize new data about the better prognosis of T1 and N0 tumors and classify those tumors into stages I and II. The adverse impact of nodal metastases on survival noted in some recent surgical series warrants placing node-positive tumors in stage III. Locally advanced unresectable (T4) tumors and extrathoracic disease (N3 or M1) are classified as stage IV.
Conclusion: This proposed staging system reconciles and updates several earlier systems, and can provide the framework for analyzing the results of prospective clinical trials aimed at improving the currently dismal prognosis of MPM.