National Institute of Arthritis and Musculoskeletal and Skin Diseases

Tuesday, Nov. 5, 1996 
4:00 PM Eastern Time 

NHLBI Communications Office 
(301) 496-4236 
Elia Ben-Ari, NIAMS 
(301) 496-8190

The November 6, 1996 issue of the Journal of the American Medical Association contains a report that older women with high bone mineral density (BMD) may have a greater risk of breast cancer than women with low BMD. Both breast cancer and bone density are thought to be related in part to a woman's lifetime exposure to estrogens, although both are influenced by a complex set of factors.

Researchers studying women aged 65 or older found that women with the highest BMD had a 2- to 2.5-fold increased risk of breast cancer compared to women with the lowest BMD. The women in the study were participants in the Study of Osteoporotic Fractures (SOF), a large observational study of white women aged 65 and older. SOF is funded by the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS) and the National Institute on Aging (NIA), which are components of the National Institutes of Health.

Researchers at four clinical centers collected breast cancer information on 8,545 women in the study. They measured the women's bone density at the beginning of the study and collected information on each woman's personal and family history of breast cancer at year 1 and an average of 3.2 years later. The researchers did not include women who reported that they were on estrogen replacement therapy at the beginning of the study. They kept track of the number of women who were diagnosed with breast cancer during the course of the study. There were 97 confirmed new breast cancer cases and 6,757 controls (women who did not develop breast cancer). The information on these women was used for the researchers' analysis, which showed a link between BMD and breast cancer risk.

The investigators suggest that bone mineral density reflects a woman's lifetime exposure to estrogens, which is influenced by factors such as age at first menstrual period, age at menopause, and natural variations in estrogen levels among women, as well as estrogen replacement therapy (ERT). The researchers speculate, therefore, that long-term exposure to estrogen in women, as measured by bone density, is an important risk factor for breast cancer.

These findings are not conclusive, and their implications for women are still unclear. The researchers did not compare breast cancer rates for women who were currently taking estrogen to those not on ERT. In addition, there was no difference in the percentage of women reporting past estrogen use among those who developed breast cancer as compared to women who did not develop breast cancer during the course of the study.

This study was not designed specifically to address the question of whether estrogen therapy affects a woman's risk of breast cancer. However, studies such as this are extremely useful in revealing associations that stimulate new research on why certain diseases and conditions arise. This could potentially lead to new intervention strategies. Information is needed from large clinical studies designed to look at the effects of estrogen therapy on bone density and on breast cancer, such as the Women's Health Initiative, to determine an overall strategy that provides the greatest health benefits and fewest risks for postmenopausal women. Until more information is available there is no reason for women to change their current health practices.

Estrogen therapy has been approved by the Food and Drug Administration for the prevention and treatment of osteoporosis. Other treatments for osteoporosis include calcium and vitamin D and/or alendronate.

Reference: J. A. Cauley, F. L. Lucas, L. H. Kuller, M. T. Vogt, W. S. Browner, S. R. Cummings. Bone mineral density predicts the risk of breast cancer in older women. The Study of Osteoporotic Fractures. JAMA, 276: 1404-1408, 1996.

Office of Scientific and Health Communications November 5, 1996

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