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HT and Breast Cancer Risk

Two new studies provide additional information on hormone therapy and breast cancer risk.

Results from two large studies provide additional information on the association between hormone therapy (HT) and breast cancer risk.

In the first study, from the Women’s Health Initiative, women who had undergone hysterectomies (age range, 50–79) received either conjugated equine estrogen (0.625 mg daily) or placebo, for an average of 7.1 years. As reported in an earlier analysis (Journal Watch Apr 27 2004), the incidence of invasive breast cancer was not higher in the estrogen group. In fact, among adherent women, breast cancer incidence was significantly lower in the estrogen group than in the placebo group (hazard ratio, 0.67). Estrogen use was associated with a higher rate of abnormal mammography findings that required short-term follow-up.

In the second study, an observational analysis of more than 30,000 black women (age, 40), the incidence of breast cancer was significantly higher among women who used any HT for at least 10 years than among women who used HT for 1 year or less (incidence rate ratio, 1.58). In a stratified analysis, this association was significant only among the leanest women (body-mass index, <25 kg/m²).

Comment: From the disparate findings of these and other studies, I’ve concluded that HT probably does modestly increase risk for breast cancer. The increase in risk appears to be lower with estrogen alone than with estrogen plus progestin. The WHI investigators describe several confounding factors that might have led to the diminution in risk among adherent women who had undergone hysterectomies, but this clearly is speculation on their part.

— Robert W. Rebar, MD

Published in Journal Watch General Medicine April 25, 2006

Citation(s):

Stefanick ML et al. Effects of conjugated equine estrogens on breast cancer and mammography screening in postmenopausal women with hysterectomy. JAMA 2006 Apr 12; 295:1647-57.

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• Medline abstract (Free)

Rosenberg L et al. A prospective study of female hormone use and breast cancer among black women. Arch Intern Med 2006 Apr 10; 166:760-5.

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• Medline abstract (Free)