The primary mediastinal growing teratoma syndrome.

We encountered a case of mediastinal immature teratoma which revealed the feature of the so-called growing teratoma syndrome. A 20-year-old male with a cough was discovered to have an abnormal shadow in the mediastinum. The serum AFP was elevated to 3600 ng/ml. The specimen with percutaneous needle biopsy revealed mature teratoma. The tumor was suspected to be mature teratoma with a malignant component because of the high level of serum AFP and he underwent chemotherapy. The serum AFP declined markedly but the tumor further enlarged. The resected tumor was diagnosed as immature teratoma, although most of the tumor tissue was mature component.