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

Abstract

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.

Histotyping of Indian thymomas: A clinicopathologic study from north India

“…The absence of thymic carcinomas in our surgically resected cases may be because these cases present at an advanced stage of the disease when surgical resection may not be a treatment option. Global data have reported no sex predilection for TETs; however, the Indian studies had shown male predominance similar to the observation in the present series101415171823. Only two studies from India demonstrated a female-predominant population1316.…”

“…The morphological classification and staging of thymomas have been extensively debated upon since decades26, with at least 24 histomorphological classifications and 15 staging systems proposed till date10. In our study, the latest modifications of WHO 2015 classification of TETs was applied which also led to the reclassification of 24 cases2727.…”

“…The worldwide incidence of thymomas is about 1.3-2.5 million per year10. Its incidence in the Indian population has not been defined and in the power analysis carried out by Marchevsky et al 11, only 20 cases of thymomas were included from India.…”

Oncological resection, myasthenia gravis and staging as prognostic factors in thymic tumours: a Chilean case series

“…Indeed, most studies demonstrate that MG prevalence on thymoma patients ranges from 30% to 50% [2]. Although there is still no consensus on an official staging classification system for thymic malignancies [3], the system originally developed by Masaoka et al [4] and subsequently modified by Koga et al [5] remains as the most widely accepted. This system (hereafter called Masaoka-Koga) establishes four stages based on the local extent of the disease [6].…”

The thymoma tale

“…On histology, the thymomas, in general, are seen to be composed of epithelial cells and lymphocytes in varying proportions. However, this seemingly innocuous admixture has led to several classification systems over decades5. The classification used currently and in this article by Guleria et al 2 is the WHO 20156, which identifies five subtypes (A, AB, B1, B2 and B3) depending on the morphology of the epithelial cells (spindloid cells, epithelioid cells or their combinations) and proportion of lymphocytes.…”