For years, medical experts believed that the association between breast cancer and breast density stemmed from the difficulty of spotting cancerous lesions (white) against dense tissue (also white). “It can be tough, like finding a polar bear in a snowstorm,” says Jokich. Mammograms in general miss 20 percent of cancers. But in women with the densest breasts, this screening can fail to spot half the cancers later found on ultrasound.
“Women need to understand that a ‘normal’ mammogram doesn’t always mean you don’t have breast cancer,” says Stacey Vitiello, MD, a breast--imaging and biopsy specialist in Montclair, New Jersey, who has worked closely with the advocacy group Are You Dense? (areyoudense.com). “Women don’t come to me for a mammogram. They come for early detection of breast cancer, and for women with dense breasts, mammograms alone are really a coin toss.”
To some experts, new findings have made density seem even more important: Researchers now know that women with denser breasts not only are at high risk of having cancers missed on mammograms but also have a greater chance of developing cancer in the first place. Why? One potential link stems from the larger number of stromal cells, a kind of connective tissue, in dense breasts. Researchers have found a relationship between stroma and an enzyme that increases the estrogen in breast tissue, which could contribute to the rise of cancer. Good news: A study published last year in the Journal of the National Cancer Institute discovered that while women with dense breasts are more likely to be stricken with breast cancer than other women, their risks of dying from it are similar.
That study suggests that women with fatty, rather than dense, breasts may also benefit from knowing their BI-RADS composition score. After following 9,232 women diagnosed with invasive breast cancer for about six and a half years, researchers were surprised to find that a specific group of breast-cancer patients had higher odds of dying: women with fattier breasts who were also obese. “Breasts with a higher percentage of fat may contribute to a tumor microenvironment conducive to cancer growth,” explains lead researcher Gretchen Gierach, PhD, of the National Institutes of Health.
What to do once you know your score
While most doctors believe that density is an important concern, they are less in step when it comes to advising women after they are notified of their density classification. Although five states require that mammogram providers disclose density as part of routine reports, many experts do not promote follow-up testing. One problem is that ultrasound and MRIs pick up too many false positives, abnormalities that look like cancer but turn out to be false alarms, says Otis W. Brawley, MD, chief medical and scientific officer of the American Cancer Society. Says UCSF’s Kerlikowske: “Some women may undergo tests that are not helpful.”
Kerlikowske believes that information about density should be used in the context of other breast-cancer risks. “Density is just another factor to weigh, along with other situations that help determine overall risk,” she says.
Monica Morrow, MD, chief of Memorial Sloan-Kettering Cancer Center’s Breast Surgical Service in New York, gives an example of the importance of considering other risk factors, based on the estimate that density increases the chances of getting cancer by four times. “In absolute terms, if a woman is otherwise low risk—young, had children before 30, no family history of breast cancer—so that her 10-year risk of breast-cancer development is 1 percent, that fourfold increase in risk due to density translates to 4 percent, a difference that clinically is not very meaningful,” she explains. “In contrast, if risk is already 5 percent, the increase to 20 percent is much more significant.”