FOUND: What It Really Means to Have Dense Breasts

A new FDA rule says women must be told if their breasts are considered dense a factor that raises breast cancer risk. What you need to know

- STACEY COLINO

After a mammogram, many women find out they have dense breasts, which increases their risk of developing breast cancer. But the question is: Why? Is it because the density makes it difficult to spot suspicious growths? Or is there something about dense breastswhich contain higher levels of fibrous and glandular tissue along with fat-that increases the risk? It turns out it's a bit of both.

Some background: Breasts are composed of a mix of fatty tissue, glandular tissue, fibrous connective tissue, blood vessels and lymphatics, explains Wendie Berg, M.D., Ph.D., a distinguished professor of radiology at the University of Pittsburgh School of Medicine. "Dense breasts have more glandular tissue, which is where the action is: More cells are dividing, increasing the risk of them becoming cancerous."

Why it matters

Breast density is often determined by genetic factors, body weight and the age at which you got your first period or reached menopause. But the use of hormones (such as oral contraceptives and hormone replacement therapy) can also influence it, says Adetunji Toriola, M.D., Ph.D., a breast cancer researcher and professor of surgery at the Washington University School of Medicine in St. Louis.

With age, some women's breasts will become less dense, particularly after menopause, but there's considerable variability on this. And a recent study suggests that the longer it takes for breast density to decline, the greater the chance of cancer.