A case of concomitant occurrence of struma ovarii and malignant transformation of cystic teratoma.

A 77-year-old woman received a total abdominal hysterectomy and bilateral salpingo-oophorectomy because of a tumor in the left ovary. The surgical specimen measured 8.5x4.5x4.0 cm, and the solid lesion measured 4.0x3.5x3.5 cm. The solid lesion was diagnosed as struma ovarii. The cyst wall partially comprised squamous epithelium-like and ciliated columnar epithelium-like cells. The tumorous lesion of the cyst wall revealed a poorly differentiated adenocarcinoma. Immunohistochemically, the tumor cells were positive for cytokeratin7, and were negative for cytokeratin20 and thyroid transcription factor-1. The authors diagnosed that struma ovarii and other parats coexisted as a poorly differentiated adenocarcinoma that had arisen from a mature ovarian cystic teratoma. As for the identification of the origin of adenocarcinomas arising from mature ovarian cystic teratomas, more cases need to be identified and investigated.