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


CONCLUSIONS
These guidelines can set the stage for reproducibility studies and the design of a clinically meaningful grading system for thymic epithelial tumors.
*Institute of Pathology, University Medical Centre Mannheim, University of Heidelberg, Mannheim, Germany; †Institute of Pathology, University of Göttingen, Göttingen, Germany; ‡Department of Pathology, Indiana University Health Pathology Laboratory, Indianapolis, Indiana; §Department of Pathology, Louis Pradel Hospital, Hospices Civils de Lyon, Lyon, France; ‖Department of Pathology, Queen Elizabeth Hospital, Hong Kong, China; ¶Department of Pathology, Shanghai Pulmonary Hospital and Tongji University School of Medicine, Shanghai, China; #University Institute of Pathology, Centre Hospitalier Universitaire Vaudois, Lausanne, Switzerland; **Department of Thoracic Surgery, Yale University School of Medicine, New Haven, Connecticut; ††Department of Respiratory Medicine, Louis Pradel Hospital, Hospices Civils de Lyon, Lyon, France; ‡‡Department of Surgery, Memorial Sloan-Kettering Cancer Center, New York, New York; §§Division of Pathology, Zurich, Switzerland; ‖‖Department of Pathology, Catholic University, Rome, Italy; ¶¶Department of Pathology, Regina Elena National Cancer Institute, Rome, Italy; ##Department of Diagnostic Pathology, Hokkaido University Hospital, Sapporo, Japan; ***Department of Pathology, AP-HP, Necker, University Paris Descartes, Paris, France; †††Department of Diagnostic Pathology, Saiseikai Central Hospital, Tokyo, Japan; ‡‡‡Diagnostic Thoracic Pathology, Royal Brompton Hospital, and Imperial College London, London, United Kingdom; §§§Department of Histopathology, The Cristie Hospital, and Institute of Cancer Sciences, The University of Manchester, Manchester, United Kingdom; ‖‖‖Institute of Pathology, University of Erlangen, Erlangen, Germany; ¶¶¶Centro Diagnostico Italiano, Milano, Italy; ###Department of Thoracic Surgery, University of Torino, Torino, Italy; and ****Department of Pathology, Memorial Sloan-Kettering Cancer Center, New York, New York.
Alexander
A
Marx
Philipp
P
Ströbel
Sunil S
SS
Badve
Lara
L
Chalabreysse
John K C
JK
Chan
Gang
G
Chen
Laurence
L
de Leval
Frank
F
Detterbeck
Nicolas
N
Girard
Jim
J
Huang
Michael O
MO
Kurrer
Libero
L
Lauriola
Mirella
M
Marino
Yoshihiro
Y
Matsuno
Thierry Jo
TJ
Molina
Kiyoshi
K
Mukai
Andrew G
AG
Nicholson
Daisuke
D
Nonaka
Ralf
R
Rieker
Juan
J
Rosai
Enrico
E
Ruffini
William D
WD
Travis
D018951:Antigens, CD20 / Q000032:analysis; D018956:CD5 Antigens / Q000032:analysis; D002277:Carcinoma / Q000737:chemistry / Q000473:pathology*; D051272:Glucose Transporter Type 1 / Q000032:analysis; D006801:Humans; D018396:Mucin-1 / Q000032:analysis; D019009:Proto-Oncogene Proteins c-kit / Q000032:analysis; D015203:Reproducibility of Results; D013945:Thymoma / Q000737:chemistry / Q000473:pathology*; D013953:Thymus Neoplasms / Q000737:chemistry / Q000473:pathology*; D014944:World Health Organization
D018951:Antigens, CD20; D018956:CD5 Antigens; D051272:Glucose Transporter Type 1; D018396:Mucin-1; D019009:Proto-Oncogene Proteins c-kit