The risks and benefits of long-term estrogen replacement therapy.

Estrogen replacement therapy (ERT) for postmenopausal women greatly reduces the risk of osteoporotic fractures, but carries an increased risk of endometrial cancer. This risk can be reduced by the addition of progestin, which does not interfere with the osteoporotic benefit of estrogen. Although long-term use data are few, there is presently little evidence for an increase or decrease in breast cancer risk associated with estrogen by itself (unopposed estrogen), or estrogen plus progestin. In contrast, a large body of evidence suggests that unopposed estrogen significantly reduces the risk of cardiovascular disease; there is no evidence that this benefit will persist when a progestin is added. The preferred method of estrogen replacement therapy, to prevent osteoporosis in a postmenopausal woman with an intact uterus, should be chosen with these different risks and benefits in mind.