Paget's disease in a retroperitoneal teratoma.

Extragonadal, mature teratomas of the retroperitoneum are rare, with fewer than 100 cases having been reported. The frequency of malignancy arising from one of the benign elements in this location is unknown, but it appears to be low. A unique feature of this case is the presence of Paget's disease in the squamous cyst lining of a mature teratoma that harbored an adenocarcinoma.