Thymom

Thymom is a term used in several languages, notably German and French, to denote a thymoma—a tumor arising from thymic epithelial cells in the anterior mediastinum. In English-language medical usage, the standard term is thymoma, while thymom may appear in non-English texts or older literature.

A thymoma is a neoplasm that can be either benign or malignant, with behavior largely depending on invasiveness rather than histologic subtype alone. It typically presents as a mass in the superior or anterior mediastinum and is often discovered incidentally on imaging. Some thymomas are associated with autoimmune conditions, most notably myasthenia gravis, pure red cell aplasia, or hypogammaglobulinemia, while many are asymptomatic.

Classification of thymomas generally relies on histology and invasiveness. The World Health Organization (WHO) system describes subtypes such as A, AB, B1, B2, and B3, which reflect the appearance of thymic epithelial cells and the accompanying lymphocyte population. A related consideration is whether the tumor remains localized or shows invasion into surrounding tissues, which influences treatment decisions and prognosis. Thymic carcinomas are a separate, more aggressive group that is distinct from thymomas.

Diagnosis typically involves imaging with CT or MRI to assess size, location, and invasion, followed by histologic confirmation when surgical resection is planned. Treatment centers on surgery, with complete resection offering the best prognosis for localized disease. Adjuvant radiotherapy may be used for invasive or incompletely resected thymomas. Chemotherapy is considered for unresectable or metastatic disease, or thymic carcinoma. Prognosis is generally favorable for early-stage thymomas but worsens with invasion or higher-grade histology.