A tumor originating from the epithelial cells of the thymus.
Comment:
Malignant lymphomas that involve the thymus, such as lymphoblastic lymphoma and Hodgkin lymphoma (erroneously termed "granulomatous thymoma" in the past), should not be regarded as thymomas. Thymoma is an uncommon tumor, best known for its association with the neuromuscular disorder myasthenia gravis. Thymoma is found in 15% of patients with myasthenia gravis.