A number of classifications have been used and proposed over the years
None of them approach the prognostic significance of staging
Some of these classifications:
Bernatz proposed the classical, descriptive system used for many years
Muller-Hermelink proposed a functional system based on perceived similarities with normal subsets of thymic epithelial cells (Kirchner)
WHO consensus essentially applied new names to the Muller-Hermelink system
Moran and Suster have proposed simplifications under a variety of names, basically grouping types A, AB, B1 and B2 because they all have similar behavior
A rough approximation of equivalents:
Bernatz
Muller-Hermelink
WHO
Moran & Suster
Spindle cell
Medullary
A
Well differentiated TEN / Low grade thymoma
Some mixed
Mixed
AB
Well differentiated TEN / Low grade thymoma
Lymphocyte rich
Predominantly cortical
B1
Well differentiated TEN / Low grade thymoma
Some mixed
Cortical
B2
Well differentiated TEN / Low grade thymoma
Epithelial rich
Well differentiated thymic carcinoma
B3
Moderately differentiated TEN / Intermediate grade thymoma
TEN = thymic epithelial neoplasm
Bibliography
Travis WD, Brambilla E, Muller-Hermelink HK, Harris CC eds. World Health Organization Classification of Tumors. Pathology and genetics of tumors of the lung, pleura, thymus and heart. IARC Press: Lyon 2004.
Bernatz PE, Harrison EG, Clagett OT. Thymoma: a clinicopathologic study. J Thorac Cardiovasc Surg. 1961 Oct;42:424-44.
Kirchner T, Schalke B, Buchwald J, Ritter M, Marx A, Müller-Hermelink HK. Well-differentiated thymic carcinoma. An organotypical low-grade carcinoma with relationship to cortical thymoma. Am J Surg Pathol. 1992 Dec;16(12):1153-69.
Suster S, Moran CA. Histologic classification of thymoma: the World Health Organization and beyond. Hematol Oncol Clin North Am. 2008 Jun;22(3):381-92.
Marchevsky AM, Gupta R, McKenna RJ, Wick M, Moran C, Zakowski MF, Suster S. Evidence-based pathology and the pathologic evaluation of thymomas: the World Health Organization classification can be simplified into only 3 categories other than thymic carcinoma. Cancer. 2008 Jun 15;112(12):2780-8.
