Thymic epithelial neoplasms.

We studied 57 tumors of the thymus seen at Vanderbilt University Medical Center between 1957 and 1982. By applying current diagnostic criteria, the classification of 13 tumors was changed. There were 45 epithelial tumors of thymus, including 32 thymomas, two thymic carcinomas, eight carcinoids, and three germinomas. The gross and microscopic features of these neoplasms overlap each other and several other tumors, but with knowledge of the variations it was usually possible to establish a diagnosis with light microscopy. In more difficult cases, electron microscopy was the most useful diagnostic method. New developments in immunologic staining were also of value. The diagnosis of thymoma was used for circumscribed and invasive neoplasms of thymic epithelium without anaplasia. Cytologically malignant thymic epithelial tumors were classified as thymic carcinoma. Thymic carcinomas were more aggressive than thymomas and were not associated with syndromes such as myasthenia gravis or anemia. Thymic carcinoids were frequently aggressive, and several of them produced corticotrophin or calcitonin. Thymic germinomas were histologically identical to testicular seminoma, but may be confused with thymoma because of their lymphocytic infiltrate. Invasive germinomas were radiosensitive.