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A Crystal Ball for Breast Cancer?

In older women, dense bones hint at cancer risk

MONDAY, July 2, 2001 (HealthDayNews) -- Someday, you might be able to check your bones to figure out your risk of developing breast cancer.

Older women with more dense bones are almost three times more likely to develop breast cancer than those with less dense bones, according to new results from an ongoing study.

"We suspect that women with high bone density may make more estrogen naturally throughout their lives, or they're more sensitive to estrogen," says Joseph Zmuda, an assistant professor of epidemiology at the University of Pittsburgh and lead author of the study.

Estrogen is the female sex hormone. Research suggests that the longer a woman is exposed to estrogen, the more likely she is to develop breast cancer, according to the National Cancer Institute.

"Bone density probably reflects a woman's natural production of these hormones throughout her life," Zmuda says.

Dr. Evan Hadley, associate director for geriatrics at the National Institute on Aging, seems to agree.

"The idea is that, through one mechanism or another, higher levels of estrogen activity may be associated with a cancer risk," Hadley says. "Estrogen may be playing the mediating role in both things -- bone density and breast cancer."

"But," Zmuda adds, "it's not that bone density causes breast cancer."

"It's important that women understand that this relationship is not a direct one," he emphasizes. "It's an indirect one."

That means bone density may be more of a marker or an indicator than a cause.

"Women should not be concerned that trying to increase their bone density will increase their risk of breast cancer," Zmuda says. "It's not the same thing."

Strong bones decrease a woman's chances of developing osteoporosis, a disease in which a person's bone mass drops, making the bones more brittle, fragile and likely to break. Ten million Americans -- 80 percent of them women, mostly over the age of 50 -- have osteoporosis, and 18 million more are at risk of developing the disease because of low bone mass, according to the National Institutes of Health.

But the same strong bones -- meaning those that have high bone mineral density -- could indicate an increased likelihood of developing breast cancer.

"Our findings suggest that two of the most common conditions affecting an older woman's health -- osteoporosis and breast cancer -- may be linked," Zmuda says. "And if we identify the common denominator for these conditions, it might improve our understanding of their causes and prevention."

Breast cancer, the most common cancer among women, strikes more than 175,000 women a year, and more than 40,000 die from the disease, according to the American Cancer Society. Women become more susceptible to the disease as they age, the society says.

The latest findings on the link between breast cancer and bone density stem from studies Zmuda and colleagues at the University of Pittsburgh's Graduate School of Public Health have been conducting for almost 15 years. Using a special imaging device known as dual energy X-ray absorptometry, the researchers periodically measure the bone density of the wrist, forearm and heel of the 8,905 women participating in the study. All participants were over 65 years of age when the study began in 1986 and had no history of breast cancer. Most are white, Zmuda says.

After six years, 315 of the women had developed breast cancer.

But those with the most dense bones had the highest rates of the cancer - they were 2.7 times more likely to develop breast cancer than women with more fragile bones, according to the study results.

An earlier report on the study, published in 1996 in the Journal of the American Medical Association, found that, after three years, women with the highest bone density were about twice as likely to develop breast cancer. At that point, 100 women had been diagnosed with breast cancer, Zmuda says.

Now, as the study progresses, the researchers also have found that women with high bone density are more likely to be diagnosed with more invasive breast cancer, as well.

Details of the latest study appear in the June 20 issue of the Journal of the National Cancer Institute.

Despite the desire some may have to point an incriminating finger at estrogen, both Zmuda and Hadley wave a caution flag.

"It would be premature to hang one's hat on that," Hadley says.

Estrogen's a definite suspect, Zmuda adds, but he stresses that researchers have more work to do before a definitive link can be proven.

What To Do

To learn more about osteoporosis, visit the Mayo Clinic online. For more on bone density, check out information from MedicineNet, an online version of the National Library of Medicine.

For more on breast cancer, go to CancerNet, sponsored by the National Cancer Institute.

If you would like cancer experts to calculate your risk of developing breast, ovarian, endometrial or cervical cancer, check out the survey provided online by the Women's Cancer Network. After completing the forms, you'll receive a personalized risk assessment, with explanations.

SOURCES: Interviews with Joseph M. Zmuda, Ph.D., assistant professor, Department of Epidemiology, Graduate School of Public Health, University of Pittsburgh, Pittsburgh, Pa.; Evan Hadley, M.D., associate director for geriatrics, National Institute on Aging, National Institutes of Health, Bethesda, Md.; June 20, 2001, Journal of the National Cancer Institute
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