Adenocarcinoma arising from mature cystic teratoma of the ovary.

An extremely rare adenocarcinoma arising from a mature cystic teratoma is reported. A 58-year-old woman underwent bilateral salpingo-oophorectomy because of a tumor in each ovary. The right ovarian tumor (solid, 9.6 x 9.6 x 6.3 cm) was a benign thecoma. Histology revealed the left ovarian cystic tumor (multilocular, 6.4 x 4.8 x 2.8 cm) was a mature cystic teratoma containing skin, fatty tissue and respiratory epithelial tissue. In addition, there was a small focal adenocarcinomatous lesion contiguous to the teratomatous ciliated columnar epithelium without stromal invasion (so-called adenocarcinoma in situ) that was suggestive of respiratory epithelium origin. However, goblet cells were present in the glandular structures of the lesion and immunohistochemical staining was segmentally strongly positive for CK20 and uniformly negative for CK7. These results suggested that the adenocarcinomatous lesion had a mucin secretory gastrointestinal phenotype. Further investigation and the collection of more cases is necessary to determine the origin and growth mechanism of adenocarcinoma arising from mature cystic teratoma of the ovary.