Thymoma and Thymic Carcinoma: An Update of the WHO Classification 2004

Abstract

When dealing with tumors of the thymus and mediastinum, both the surgeon and the pathologist are confronted with a vast variety of different pathohistologic entities, among which epithelial tumors, namely thymomas and thymic carcinomas, are the most frequent. Intimate knowledge of the different entities and their anticipated clinical outcome is required to meet diagnostic and therapeutic challenges. We herein briefly update the reader with the most important new changes in the 2004 WHO classification of tumors of the thymus and to important new trends in the treatment of some of these tumors.

Evidence‐based pathology and the pathologic evaluation of thymomas

“…14,16,17,[29][30][31][32][33][34][35][36][37][38][39][40] What Levels of 'Best Evidence' Are Currently Available?…”

“…13 Thymic carcinoma was initially classified in 1999 as Thymoma C but in the most current version of the schema it is listed as thymic carcinoma. 14 The WHO terminology was intended to provide a translation formula to facilitate comparison among preexisting nomenclatures but it has become the de-facto classification system of thymomas, widely used in many countries.…”

“…12 Clinical studies have also raised questions regarding the predictive value of the WHO classification scheme of thymomas in helping to select various therapeutic modalities such as neoadjuvant therapy. 7,14,[16][17][18] For example, a recent review article by Detterbeck, 7 a thoracic surgeon, concluded that the prognosis of patients with thymomas subtypes A, AB, and B1 through B3 is variable and that the issue of how the WHO classification should be used in the clinical setting remains unclear.…”

Molecular Markers for Patients with Thymic Malignancies: not Feasible at Present?

“…The tumor cells in thymomas closely resemble the normal cells of the thymus (regardless of the presence and relative numbers of non-neoplastic lymphocytes), grow slowly, and rarely spread beyond the thymus (Polo et al, 2013). According to the WHO classification, thymomas can be divided into five subgroups (A, AB, B1, B2, B3), depending on cancer cell shape, degree of atypia, and number of intratumoral thymocytes (Strobel et al, 2005). Differently from thymomas, the epithelial component proliferates of thymic carcinomas are not characterized by the typical lymphocytic admixture (Kelly, 2013).…”

Spontaneous Thymoma in a Juvenile Cynomolgus Macaque (Macaca fascicularis)

“…The World Health Organization (WHO) classification system uses the shape and characteristics of the epithelial cells and the proportion of lymphocytes within the tumor to categorize them into types A, AB, B1, B2, or B3. This classification does not extend to thymic carcinoma, which is designated separately (Strobel et al 2005). However, a recent publication employing meta-analysis of published data, which included survival times of patients with specific tumor types, found significant survival differences in only three types of tumors, A, AB, and B1 combined; B2; and B3.…”