[Mediastinal seminoma difficult to differentiate from thymoma through preoperative biopsy; report of a case].

A case of a 36-year-old male patient with mediastinal seminoma is presented. He consulted a physician with a complaint of back pain and an abnormal shadow was detected on chest X-ray. Chest computed tomography (CT) scan revealed a pulmonary nodule and an anteriormediastinal mass. Preoperative percutaneous needle biopsy suggested that the tumor was similar to thymoma. Complete surgical excision of the mediastinal mass was performed. Immunohistochemical studies showed positive staining of the tumor cells with placental alkaline phosphatase. The final diagnosis was seminoma. Additional postoperative chemotherapy (cisplatin + etoposide) was done. He is alive and well 34 months after the operation.