Malignancy arising in endometriosis associated with unopposed estrogen replacement

Malignant transformation of endometriosis is a well documented phenomenon. Although it occurs most commonly in the ovaries, there have been approximately 50 reported cases of extraovarian malignant transformation of endometriosis. This paper presents two cases of malignancy arising from a dormant focus of endometriosis after total abdominal hysterectomy, bilateral salpingo-oophorectomy, and exogenous estrogen replacement therapy. These malignancies are often well differentiated and may behave similarly to estrogen-induced endometrial carcinomas. After surgical castration of a premenopausal woman with endometriosis, the use of progestins in replacement therapy may reduce the risk of malignancy arising in endometriosis.