A neoplasm in the anterior mediastinum, originating from thymic tissue, usually benign, and frequently encapsulated; occasionally invasive, but metastases are rare; histologically, consists of any type of thymic epithelial cell as well as lymphocytes that are usually abundant. Malignant lymphoma that involves the thymus, Hodgkin disease, should not be regarded as thymoma.
[thymus + G. -oma, tumor]
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