Primary thymic carcinoma. An unusual case originating in a lymphocytic rich thymoma

A case of thymic carcinoma arising within a lymphocyte rich thymoma is reported. The undifferentiated carcinoma contained cellular elements resembling choriocarcinoma but could be differentiated therefrom by positive staining for prekeratin antigen and an absence of staining for B-HCG antigen utilizing immunohistochemical techniques.