ITMIG consensus statement on the use of the WHO histological classification of thymoma and thymic carcinoma: refined definitions, histological criteria, and reporting

J Thorac Oncol. 2014 May;9(5):596-611. doi: 10.1097/JTO.0000000000000154.


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.

Publication types

  • Consensus Development Conference
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antigens, CD20 / analysis
  • CD5 Antigens / analysis
  • Carcinoma / chemistry
  • Carcinoma / pathology*
  • Glucose Transporter Type 1 / analysis
  • Humans
  • Mucin-1 / analysis
  • Proto-Oncogene Proteins c-kit / analysis
  • Reproducibility of Results
  • Thymoma / chemistry
  • Thymoma / pathology*
  • Thymus Neoplasms / chemistry
  • Thymus Neoplasms / pathology*
  • World Health Organization


  • Antigens, CD20
  • CD5 Antigens
  • Glucose Transporter Type 1
  • Mucin-1
  • Proto-Oncogene Proteins c-kit