Exacerbation of endometriosis as a result of premenopausal tamoxifen exposure.

A 41-year-old woman with a history of endometriosis had breast carcinoma diagnosed and treated with tamoxifen. A pelvic mass was subsequently diagnosed and observed on serial ultrasonographic examinations to increase in size. At surgery extensive endometriosis was found. Exacerbation of endometriosis by tamoxifen may become more common as tamoxifen is used more frequently to reduce the risk of breast cancer among premenopausal women.