Mature cystic teratoma with malignant transformation to adenocarcinoma.

An anterior mediastinal tumor had been found in a 65-year-old woman 10 years previously, and she had been followed-up under the diagnosis of a mature cystic teratoma. Changes in the structure of the inside of the mediastinal cystic tumor were observed on a chest computed tomography image, and she was referred to our hospital for surgical intervention. The tumor was removed and was determined to be a mature teratoma. An adenocarcinoma was also observed in part of this cystic lesion. From these findings, the lesion was diagnosed as a malignant change in a mediastinal mature teratoma. Because few if any changes tend to be observed in the cystic wall of such cases, an aggressive resection of such mature cystic teratomas is therefore recommended.