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Studies Point to Reasons for Mammograms in 40s

Women With Dense Breasts or a Family History of Breast Cancer May Want to Consider Screening in Their 40s

Family History or Dense Breast Tissue Doubles Risk continued...

The first study used four different models to simulate the benefits and harms of screening mammography in women ages 40 to 49.

That study found that women in their 40s need to have double the average risk of getting breast cancer to get the same degree of benefit from regular mammograms, meaning every other year, as women in their 50s.

"Between 40 to 49, the chance of developing breast cancer is under 2%, so even when you double that, it's still low," says researcher Jeanne S. Mandelblatt, MD, MPH, associate director for population sciences at Georgetown University Medical Center's Lombardi Comprehensive Cancer Center in Washington, D.C.

In a companion study, researchers asked what risk factors might actually double a woman's risk for breast cancer in her 40s.

For that study, researchers reanalyzed data from 66 published studies and included data on more than 380,000 women who are being tracked through the Breast Cancer Surveillance Consortium, a network of seven mammography registries.

Out of 13 distinct risk factors identified through the studies and registries, only two fully doubled a woman's risk for breast cancer in her 40s.

"To have a twofold increase in risk, you need to have a first-degree relative -- a mother, daughter, or sister -- with breast cancer. Or you need to have extremely dense breasts. There aren't that many women who have either of those conditions," Mandelblatt says.

For women with more than one first-degree relative with breast cancer, the risks were even higher -- four to 12 times greater than average.

If a first-degree relative was diagnosed before age 40, a woman's risk of breast cancer was three times higher than average.

The issue of breast density is a complicated one, researchers admit, because density can only be determined by first getting a mammogram.

Experts don't recommend that women get a baseline mammogram to discover breast density.

"Mammography density is sort of a newer area," says researcher Heidi D. Nelson, MD, MPH, an investigator at the Oregon Evidence-based Practice Center and the Knight Cancer Institute at Oregon Health & Science University in Portland.

"Radiologists aren't in good agreement about how to read breast density, and we're not sure how to drive that car, yet, really," Nelson says. "So it would be good to maybe wait for more research about exactly how to make decisions with that information."

But Nelson says the study should also comfort women who worry that things like physical inactivity and body weight might put them at increased risk for breast cancer. The study found those had relatively little influence on a person's risk. Other factors that didn't appear to raise risk substantially included race, smoking, and alcohol use.

"What's really reassuring is that there are a lot of risk factors that really don't have a huge increase in risk attached to them," says Nelson.

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