Squamous cell carcinoma of the thymus. An analysis of eight cases.

Eight cases of squamous cell carcinoma of the anterior mediastinum, most likely derived from the thymus, are presented. Seven were male and one female ranging in age from 39 to 65 years; the average was 55.5 years. There were no cases associated with any paraneoplastic syndromes. They possessed common morphological characteristics. Grossly, the tumors resembled malignant thymoma. Invasion of the lung and metastases to regional lymph nodes were frequent. Often observed microscopically were foci of sharply defined keratinization resembling Hassall's corpuscles, no radial arrangement of tumor cells at the periphery of nests, and broad, fibrotic, or hyalinized stroma. Admixture of a few lymphoid cells and some features transitional to thymoma were also observed in some parts of tumors. However, undoubtedly carcinomatous areas were present in some or large parts of all the tumors, where individual cells possessed a vesicular nucleus and a prominent round nucleolus. These features were distinct from those of bronchogenic squamous cell carcinoma and other thymic tumors, although they appeared to be related to thymoma. Treatment of choice is radical surgery and postoperative radiotherapy, because of relatively high radiosensitivity. Prognosis of patients was relatively good. From analyses of cases it is concluded that squamous cell carcinoma of the thymus should be separated from ordinary thymoma of the epithelial type, and that squamous cell carcinoma involving both the thymus and lungs should be carefully examined for the primary site of growth.