The International Association for the Study of Lung Cancer Pleural Mesothelioma Staging Project: Proposal for Revision of the TNM Stage Groupings in the Forthcoming (Ninth) Edition of the TNM Classification for Pleural Mesothelioma

Introduction: The eighth edition of the TNM classification of pleural mesothelioma (PM) saw substantial changes in T and N components and stage groupings. The International Association for the Study of Lung Cancer collected data into a multinational database to further refine this classification. This ninth edition proposal incorporates changes proposed in the clinical (c)T component but not the pathologic T component, to include size criteria, and further refines TNM stage groupings for PM. Methods: Data were submitted through electronic data capture or batch transfer from institutional databases. Survival was measured from diagnosis date. Candidate stage groups were developed using a recursive partitioning and amalgamation algorithm applied to all cM0 cases for clinical stage and subsequently for pathologic stage. Cox models were developed to estimate survival for each stage group. Results: Of 3598 submitted cases, 2192 were analyzable for overall clinical stage and 445 for overall pathologic stage. Recursive partitioning and amalgamation generated survival tree on overall survival outcomes restricted to cM0, with newly proposed (ninth edition) cT and cN component- derived optimal stage groupings of stage I (T1N0), II (T1N1; T2N0), IIIA (T1N2; T2N1/2; any T3), IIIB (any T4), and IV (any M1). Although cT and pathologic T descriptors are different in the ninth edition, aligning pathologic stage groupings with clinical stage produced better discrimination than did retaining eighth edition pathologic stage groupings. Conclusions: To our knowledge, this revision of the clinical TNM classification for PM is the first to incorporate the measurement-based proposed changes in cT category. The pathologic TNM aligns with clinical TNM. (c) 2024 International Association for the Study of Lung Cancer. Published by Elsevier Inc. All rights reserved.