The IASLC 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 tumor, node and metastases (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 in order to further refine this classification. This 9th edition proposal incorporates changes proposed in the clinical (c)T component, but not the pathologic (p)T component, to include size criteria, and further refines TNM stage groupings for PM. Methods Data were submitted via electronic data capture (EDC) or batch transfer from institutional databases. Survival was measured from diagnosis date. Candidate stage groups were developed using a recursive partitioning and amalgamation (RPA) algorithm applied to all cM0 cases for clinical stage and subsequently for pathological stage. Cox models were developed to estimate survival for each stage group. Results Of 3598 submitted cases, 2192 were analyzable for overall cStage and 445 for overall pStage. RPA generated survival tree on OS outcomes restricted to cM0 with newly proposed (9th 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 pT descriptors are different in the 9th edition, aligning pStage groupings with cStage produced better discrimination than retaining 8th edition pStage groupings. Conclusions This revision of the clinical TNM classification for PM is the first to incorporate the measurement-based proposed changes in clinical T category. The pathological TNM aligns with clinical TNM.