ITMIG Consensus Statement on the Use of the WHO Histological Classification of Thymoma and Thymic Carcinoma: Refined Definitions, Histological Criteria, and Reporting

• Published in: Journal of thoracic oncology Vol. 9; no. 5; pp. 596 - 611
• Main Authors: Marx, Alexander, Ströbel, Philipp, Badve, Sunil S., Chalabreysse, Lara, Chan, John K.C., Chen, Gang, de Leval, Laurence, Detterbeck, Frank, Girard, Nicolas, Huang, Jim, Kurrer, Michael O., Lauriola, Libero, Marino, Mirella, Matsuno, Yoshihiro, Molina, Thierry Jo, Mukai, Kiyoshi, Nicholson, Andrew G., Nonaka, Daisuke, Rieker, Ralf, Rosai, Juan, Ruffini, Enrico, Travis, William D.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: United States Elsevier Inc 01.05.2014; Copyright by the European Lung Cancer Conference and the International Association for the Study of Lung Cancer
• Subjects: Antigens, CD20 - analysis; Carcinoma - chemistry; Carcinoma - pathology; CD5 Antigens - analysis; Diagnostic criteria; Glucose Transporter Type 1 - analysis; Histological classification; Humans; Mucin-1 - analysis; Proto-Oncogene Proteins c-kit - analysis; Reproducibility of Results; Thymic carcinoma; Thymoma; Thymoma - chemistry; Thymoma - pathology; Thymus Neoplasms - chemistry; Thymus Neoplasms - pathology; World Health Organization; Thymoma; Thymic carcinoma; Diagnostic criteria; Histological classification
• ISSN: 1556-0864; 1556-1380
• DOI: 10.1097/JTO.0000000000000154

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. 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. 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. These guidelines can set the stage for reproducibility studies and the design of a clinically meaningful grading system for thymic epithelial tumors.