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Journal of Thoracic Oncology:
doi: 10.1097/JTO.0000000000000154
Special Article

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

Marx, Alexander MD*; Ströbel, Philipp MD*†; Badve, Sunil S. MD; Chalabreysse, Lara MD§; Chan, John K.C. MD; Chen, Gang MD, PhD; de Leval, Laurence MD, PhD#; Detterbeck, Frank MD**; Girard, Nicolas MD, PhD††; Huang, Jim MD‡‡; Kurrer, Michael O. MD§§; Lauriola, Libero MD‖‖; Marino, Mirella MD¶¶; Matsuno, Yoshihiro MD##; Molina, Thierry Jo MD, PhD***; Mukai, Kiyoshi MD†††; Nicholson, Andrew G. MD‡‡‡; Nonaka, Daisuke MD§§§; Rieker, Ralf MD‖‖‖; Rosai, Juan MD¶¶¶; Ruffini, Enrico MD###; Travis, William D. MD****

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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.

Copyright © 2014 by the International Association for the Study of Lung Cancer

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