The effects of menopausal hormone therapy on breast cancer: Evidence from the women's health initiative randomized placebo-controlled trials

Abstract

Within the past decade, comprehensive evidence about the risks and benefits of menopausal hormone therapy (MHT), formerly referred to as hormone replacement therapy (HRT), has been published from the National Institutes of Health (NIH)-funded Women's Health Initiative (WHI) randomized placebo-controlled trials of combined estrogen plus progestin therapy and estrogen-only therapy. Current, widely accepted practice, which arose after two 1975 landmark studies reported increased endometrial cancer risk in women who were using unopposed estrogen, i.e., estrogen-only, is to administer estrogen to women who have undergone prior hysterectomy (with either surgical or natural menopause) and to use a combination of estrogen and progesterone (E plus P) in women with an intact uterus. Progesterone is added in these women to prevent endometrial hyperplasia, which is known to be increased by unopposed estrogen, and is believed to prevent endometrial carcinoma, the risk of which increases substantially with long duration estrogen-only use and remains elevated for several years after discontinuation of hormone therapy. Understanding results of these trials is extremely helpful as many women have used various forms of hormone replacement and are often concerned about the associated cancer risk. In addition, healthy women without breast cancer histories will often inquire about the use of hormone replacement and the potential impact on breast cancer risk. © 2011 Springer Science + Business Media.