Older women are more likely to get breast cancer if they have high bone density, say University of Pittsburgh researchers

PITTSBURGH, June 19 – Investigators from the University of Pittsburgh Graduate School of Public Health have found that older women with high bone mineral density (BMD) are nearly three times as likely to develop breast cancer as are older women with low BMD, and that their tumors tend to be at an advanced stage at diagnosis.

Results of the study are published in the June 20 issue of the Journal of the National Cancer Institute. This study confirms a smaller University of Pittsburgh study published in the Journal of the American Medical Association in 1996.

"This study shows that there is an inverse relationship between osteoporosis and invasive breast cancer, two of the most common and important conditions affecting an older woman's health," said Jane Cauley, D.P.H., associate professor of epidemiology and study co-author. "The results suggest that bone mineral density is one of the most powerful predictors of breast cancer, especially advanced breast cancer, among elderly women."

Investigators stress than high BMD itself is not the cause of breast cancer, but a marker for hormone levels, and that women should not discontinue their efforts to maintain bone mass through diet or medication.

"Sex steroid hormones, like testosterone and estrogen, or other growth promoting hormones, may be the link to breast cancer," said Dr. Cauley, "and BMD may reflect a woman's long-term exposure to these hormones. Further studies are needed to identify the common denominator."

At the start of the study, researchers measured BMD at the wrist, forearm and heel in 8,905 women, all of whom were at least 65 years of age and had no history of breast cancer. The women then were monitored for occurrence of breast cancer over a period of 6.5 years.

A total of 315 women developed breast cancer. Analysis showed that women with the highest BMD at all three skeletal sites were nearly three times more likely to develop breast cancer than were women with the lowest BMD at the three skeletal sites. Moreover, this risk was greater for more advanced breast cancer than it was for early-stage cancer.

Participants diagnosed with breast cancer were slightly older and heavier than participants without breast cancer. Having a first-degree relative with breast cancer or a history of benign breast disease was also associated with the development of breast cancer in these participants. However, risk factors such as age, weight, family history and benign breast disease did not account for the link between high BMD and breast cancer.

All women in the current study were participants in the ongoing multi-site Study of Osteoporotic Fractures, a prospective study involving the University of Pittsburgh; the University of Maryland, Baltimore; the University of Minnesota, Minneapolis; the Kaiser Permanente Center for Health Research, Portland, Oregon and the University of California, San Francisco.

The study is supported by the National Institute of Arthritis and Musculoskeletal and Skin Diseases and the National Institute on Aging.