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High bone density increases risk of breast cancer

Scott Gottlieb New York

Older women with high bone density are about twice as likely to develop breast cancer, a new study has found.

These results add to existing evidence that suggests that older women who have low bone mass have a decreased risk of breast cancer and, conversely, that higher bone density is associated with increased risk of breast cancer.

Bone mineral density can be an accurate marker of the body’s response to oestrogen, in that women with higher bone density are thought to be physiologically more sensitive to the hormone’s effects than women with lower bone density.

Because oestrogens have also been linked to risk of breast cancer, researchers in this study sought to determine if bone density might help also to predict the risk of breast cancer in older women.

The study, led by Dr Jane Cauley of the University of Pittsburgh Medical Center, followed the health history of 8905 women who were 65 years or older and without breast cancer.

After six years it found that the women who scored highest on three types of bone mineral density tests (performed on the bones of the wrist, arm, and heel) were also more likely to develop breast cancer (Journal of the National Cancer Institute 2001;93:930-936).

During the six year period a total of 315 women (3.5%) developed breast cancer.

After adjusting for other risk factors that contribute to breast cancer, such as age and obesity, the investigators found that the risk for women with the highest bone density for all three skeletal sites was 2.7 times greater than that for women with the lowest measurement of bone density for all three sites.

"The results suggest that bone mineral density is one of the most powerful predictors of breast cancer, especially advanced breast cancer, among elderly women," Dr Cauley said.

Bone density, she said, is not a cause of breast cancer, but it is an indirect measure of levels of hormone such as testosterone and oestrogen that have been linked to bone density and breast cancer.

Oestrogen, for example, is known to play a role in risk of breast cancer because women who menstruate at an early age, have a late age of menopause, or are childless, have greater exposure to the hormone—and an increased risk of cancer.

Dr Carmen Rodriguez of the American Cancer Society said that a bone density test may eventually be important in assessing risk of breast cancer, but " we shouldn’t use it now" because there are too many unanswered questions about accuracy.

"There are much better markers for breast cancer right now," said Dr Rodriguez.

Also, the study looked at older women, and it is not clear how the tests could be used for women under 65. In addition, the study's results showed that women who developed breast cancer were more likely at diagnosis to have a more advanced stage of the disease.

"These findings suggest an association between osteoporosis and invasive breast cancer, two of the most prevalent conditions affecting an older woman’s health," the authors concluded.
 
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