Evolution of Classification of Thymic Epithelial Tumors in the Era of Dr Thomas V. Colby

Context.—Numerous histomorphologic and staging classifications of thymic epithelial tumors (TETs) have been proposed during the last century, suggesting that the classification of these tumors is challenging and controversial. Difficulties of classifying TETs include various combinations of epithelial cells and lymphocytes and the paucity of these tumors. The prognostic significance, specifically of the histomorphologic classifications, has been debated. Early classifications were also challenged by the uncertainty of the neoplastic component(s) of the tumor.Objective.—To discuss the evolution of the histomorphologic classification and the staging system of TET. Controversies and problems of some classifications and their importance for therapeutic management and prognosis will be reviewed. Classifications that incorporated new concepts and approaches at the time or outcome studies will be highlighted. Current classifications will be discussed and the staging system that was recently proposed for the upcoming eighth American Joint Committee on Cancer staging will be described.Data Sources.—Search of literature database (PubMed) and current (2015) World Health Organization classification.Conclusions.—Histomorphologic and staging classifications of TET have evolved during the last century and especially during the era of Thomas V. Colby, MD. Evidence supports that the staging system has prognostic implications independent of and superior to the histomorphologic classification. Histomorphology appears to be important for biologic features of TET.