Immunologic and ultrastructural characterization of the small cell population in malignant thymoma.

A case of malignant thymoma is presented. The electron microscopic (EM) findings of the lymphocyte-epithelial relationships were similar to these previously described. Utilizing specific monoclonal antibodies to differentiate thymocytes from T-lymphocytes, the small cell population with ultrastructural features of lymphoid cells consisted of true thymocytes rather than peripheral T-lymphocytes. The latter finding may prove to be of importance in differentiating thymomas from reactive or most neoplastic lymphocytic processes involving the thymus gland.