Hormone Replacement Therapy Increases the Risk of Breast Cancer

One of the most alarming findings of the National Institutes of Health (NIH) Women's Health Initiative (WHI) last year was the significant increase in the risk of invasive breast cancer among menopausal women who took combined conjugated equine estrogen and medroxyprogesterone acetate therapy (Prempro™).   These data were at least reassuring (although confusing) in that there was no difference in mortality between the treatment group and the placebo group.  The Million Woman Study recently published in the British medical journal the Lancet (8/03) compounds the WHI data. In this study, women receiving a combination of estrogen and progestin not only had an increased risk of breast cancer, but they had a 22% higher risk of death from breast cancer compared with women who weren't receiving hormonal therapy.

The Million Woman Study surveyed 1.1 million women in the United Kingdom aged 50 to 64. They were recruited between 1996 and 2001 and tracked for cancer incidence and death.

Based upon existing statistical data, we know that out of 1,000 postmenopausal women between the ages of 50 and 60 who don't use HRT, there will be approximately 20 breast cancer cases diagnosed.  However, according to this study, in every 1,000 women who begin 10 years of HRT at the age of 50, there will be five extra cases among estrogen-only users, and 19 additional breast cancers among estrogen-progestin combination users.

These data are consistent with the WHI data in that the group of women on combined HRT fared worse than the group of women on estrogen alone.  This raises many questions, including whether women currently taking either of these treatment regimens should make changes.  As always, these decisions should be based upon consultation with your personal physician rather than a rash interpretation of how a clinical trial might apply to you.

Created: 9/4/2003  -  Donnica Moore, M.D.