Primary mediastinal seminoma.

Four new cases of primary mediastinal seminoma are presented, and the 103 previously reported cases reviewed. All of the tumors occurred in the anterior mediastinum, and generally appeared as lobulated noncalcified masses on chest radiography. Most patients were in the third and fourth decades, and about 30% were asymptomatic at the time of initial diagnosis. Although mediastinal seminoma is not commonly considered a cause of superior vena caval obstruction, about 10% of patients experience it. The tumors are radiosensitive and potentially radiocurable. A striking reduction in size of the tumor may be noted after radiation therapy. Prognosis is generally good, with a 5-year survival rate of 75%. The controversy surrounding histogenesis of this tumor is reviewed, and the pathologic criteria for making the diagnosis presented.