ITMIG consensus statement on the use of the WHO histological classification of thymoma and thymic carcinoma: refined definitions, histological criteria, and reporting
Alexander Marx, Philipp Ströbel, Sunil S Badve, Lara Chalabreysse, John K C Chan, Gang Chen, Laurence de Leval, Frank Detterbeck, Nicolas Girard, Jim Huang, Michael O Kurrer, Libero Lauriola, Mirella Marino, Yoshihiro Matsuno, Thierry Jo Molina, Kiyoshi Mukai, Andrew G Nicholson, Daisuke Nonaka, Ralf Rieker, Juan Rosai, Enrico Ruffini, William D Travis, Alexander Marx, Philipp Ströbel, Sunil S Badve, Lara Chalabreysse, John K C Chan, Gang Chen, Laurence de Leval, Frank Detterbeck, Nicolas Girard, Jim Huang, Michael O Kurrer, Libero Lauriola, Mirella Marino, Yoshihiro Matsuno, Thierry Jo Molina, Kiyoshi Mukai, Andrew G Nicholson, Daisuke Nonaka, Ralf Rieker, Juan Rosai, Enrico Ruffini, William D Travis
Abstract
Introduction: The 2004 version of the World Health Organization classification subdivides thymic epithelial tumors into A, AB, B1, B2, and B3 (and rare other) thymomas and thymic carcinomas (TC). Due to a morphological continuum between some thymoma subtypes and some morphological overlap between thymomas and TC, a variable proportion of cases may pose problems in classification, contributing to the poor interobserver reproducibility in some studies.
Methods: To overcome this problem, hematoxylin-eosin-stained and immunohistochemically processed sections of prototypic, "borderland," and "combined" thymomas and TC (n = 72) were studied by 18 pathologists at an international consensus slide workshop supported by the International Thymic Malignancy Interest Group.
Results: Consensus was achieved on refined criteria for decision making at the A/AB borderland, the distinction between B1, B2, and B3 thymomas and the separation of B3 thymomas from TCs. "Atypical type A thymoma" is tentatively proposed as a new type A thymoma variant. New reporting strategies for tumors with more than one histological pattern are proposed.
Conclusion: These guidelines can set the stage for reproducibility studies and the design of a clinically meaningful grading system for thymic epithelial tumors.
Source: PubMed