Combined thymoma-thymic seminoma. Report of 2 cases of a heretofore unreported association

Two cases of a primary mediastinal tumor showing both thymoma and seminoma elements are presented. The patients were 2 men, aged 32 and 34 years, respectively. Clinically, both patients presented with symptoms related to their mediastinal masses, namely, chest pain and shortness of breath. Neither patient had any previous history of malignancy elsewhere. Diagnostic imaging revealed the presence of large anterior mediastinal masses. Both patients underwent thoracotomy with complete resection of their tumors. Grossly, the lesions measured 6 and 8 cm in greatest diameter, respectively and were tan and firm without areas of hemorrhage or necrosis. Both tumors appeared to be well circumscribed and grossly not involving any adjacent structures. Histologic sections showed the presence of distinct areas in the same tumor mass corresponding to conventional thymoma, whereas other areas corresponded to seminoma. Both components appeared to be present in almost equal proportions in the tumor. Immunohistochemical studies showed distinct labeling for each component: the thymoma component was positive for CAM5.2, Pax8, and cytokeratin 5/6; the seminoma component was positive for CAM5.2, SALL4, OCT3/4, and placental-like alkaline phosphatase. Both patients are currently alive and well 12 and 18 months after surgery, respectively. The cases herein described highlight the importance of ample sampling in mediastinal tumors and document for the first time the existence of combined thymoma-thymic seminomas.