Background: Although thymic epithelial tumors (TETs) are rare, they account for approximately 50% of anterior mediastinal tumors. These tumors, including thymomas and thymic carcinomas, are distinguished by specific histological and immunohistochemical characteristics, necessitating the development of precise classifications. The revised World Health Organization (WHO) classification in 2021 has refined diagnostic criteria, identified new entities and variants, and integrated advances in immunohistochemistry and molecular biology. The main objective of our work is to describe the histopathological aspects of thymic epithelial tumors and reclassify them according to the new 2021 WHO classification, as well as to compare the histopathological findings with clinical and radiological data.
Methods: This is a single-center, descriptive, retrospective study involving 100 patients diagnosed with and operated on for thymic epithelial tumors. The cases were collected from the Department of Pathology and Cytology at Abderrahman Mami Hospital in Ariana, spanning from January 2010 to December 2022.
Results: The study included 54 women and 46 men (sex ratio: 0.85). The average age was 50 years, with extremes ranging from 12 to 81 years. The primary reason for consultation was myasthenia (44%, n=44), which was preferentially associated with type B2 thymomas (52.3%). Thoracic X-rays, performed as a first-line examination, revealed a mediastinal opacity in 48% of cases. However, chest Computed Tomography scans were the reference examination, allowing better characterization of mediastinal masses and detecting signs of locoregional invasion in 11% of cases. Surgical resection was performed in all cases, preceded by a transpleural biopsy in 15% of cases. Histological examination revealed 95 cases of thymomas and 5 cases of thymic carcinomas. Type B2 thymomas were the most frequent (41.1% of cases), followed by type AB thymomas (23.1%) and type B1 thymomas (18.9%). Immunohistochemically, the epithelial cells expressed epithelial membrane antigen (EMA) and cytokeratin (CK). The lymphoid component in thymomas showed a B-cell phenotype, with CD20 expression in 5 cases, and a T-cell phenotype, expressing CD3 in 52 cases. Immature T lymphocytes expressed CD1a, Terminal deoxynucleotidyl transferase (TdT), and CD99 markers in all cases. Regarding thymic carcinomas, each subtype had specific immunohistochemical markers. The Masaoka-Koga classification revealed that stage IIb was the most common for thymomas, with a frequency of 52.6%.
Conclusions: Though rare, TETs have distinct characteristics that require a multidisciplinary approach, incorporating advances in pathology, radiology, and molecular biology. A better understanding of these tumors allows for optimized treatment, particularly through precise surgery and rigorous evaluation of clinical and radiological data. This study highlights the importance of the updated classification of thymic epithelial tumors in refining diagnosis and improving patient management.
