Thymomas

Thymomas are tumors arising from thymic epithelial cells in the anterior mediastinum. They are the most common thymic neoplasm and are distinct from thymic carcinoma, which is more aggressive. Thymomas are generally slow-growing and vary in histology and behavior.

Classification and staging guide management and prognosis. The World Health Organization (WHO) system groups thymomas by histology into types A, AB, B1, B2, and B3, reflecting differences in epithelial cell appearance and lymphocyte content. Staging is commonly described by the Masaoka-Koga system, ranging from stage I (encapsulated, no invasion) to stage IV (advanced or metastatic disease). The stage at diagnosis and completeness of surgical removal are major determinants of outcome.

Clinical features often include no symptoms or a chest mass discovered incidentally. When symptoms occur, they may include chest discomfort, cough, or dyspnea due to tumor mass effect. A notable association is myasthenia gravis (MG), occurring in roughly 30–50% of thymoma patients, with MG symptoms potentially improving after tumor removal. Other autoimmune conditions linked to thymoma include pure red cell aplasia and hypogammaglobulinemia.

Diagnosis typically begins with imaging, usually chest computed tomography (CT) or magnetic resonance imaging (MRI) to characterize a mediastinal mass. Blood tests for MG (antibodies to acetylcholine receptors) may be performed if MG symptoms are present. Definitive diagnosis is based on histology, often post-surgical resection; biopsy may be used selectively to guide treatment when surgery is not immediately planned.

Management is multidisciplinary. For localized thymoma, surgical resection (thymectomy or thymomectomy) is the principal treatment, with adjuvant radiotherapy considered for invasive disease. Advanced, unresectable, or metastatic thymoma may require chemotherapy, radiotherapy, or a combination. Thymic carcinoma requires more aggressive treatment. Follow-up includes periodic imaging and monitoring for MG symptoms. Prognosis is generally favorable for early-stage thymoma with complete resection but worsens with higher stage and incomplete removal.