A pregnant woman with clear cell adenocarcinoma of the ovary arising from endometriosis and with benign and borderline adenofibroma of the clear cell and endometrioid types.

We encountered a case of ovarian cancer in a 33-year-old, 8-week pregnant woman. Histological examination revealed both a transitive form of ovarian endometriosis with marked decidual changes due to pregnancy and clear cell carcinoma. Benign and borderline clear cell adenofibroma and benign and borderline endometrioid adenofibroma were also found. Parts of these adenofibromas showed transformation to clear cell carcinoma. This case suggests that clear cell carcinoma can arise from clear cell adenofibromas and/or ovarian endometriosis, even in young patients.