Dense Breasts May Be a Risk Factor for Breast Cancer

Breast cancer risk assessment and prevention should start much earlier in life than it currently does, say Canadian researchers who examined breast cancer risk factors in young women.

The study was published in the medical journal The Lancet Oncology.

The study of 400 women, ages 15 to 39, and their mothers found that breast tissue composition in young women may be associated with their risk for breast cancer in middle age and older.

"It is known that the breast is most susceptible to the effects of carcinogens at early ages. Our findings suggest that differences in breast tissue composition in early life may be a potential mechanism for this increased susceptibility," says lead researcher Dr. Norman Boyd, of the Campbell Family Institute for Breast Cancer Research, Toronto.

"By identifying the environmental and genetic factors that influence breast tissue composition early in life, we may be able to develop safe and effective methods of prevention," he says.

Starting Prevention Earlier than Later

In this study, the researchers looked at the amount of dense breast tissue (mammographic density, or MD), which varies considerably among women and is a significant risk factor for breast cancer in middle-aged and older women.

Experts know that the risk of breast cancer increases as MD increases.

However, little has been known about the development of MD early in life or how the MD of young women is related to their height, weight, age, and their mother's MD.

The study authors conclude that a high degree of mammographic density in middle age, when it is a strong risk factor for breast cancer, may arise from the subset of the population with the greatest amount of fibro-glandular tissue in early life.

This is when susceptibility to potential carcinogens is greatest.

"Interventions directed at the prevention of breast cancer may therefore be more effective if they are started in early life rather than adult life," Dr, Boyd says.

Harder to Detect Cancer in Dense Breasts

For years, researchers have known that breast density is almost as important as age in predicting who will develop breast cancer.

But now they are discovering how the density of a woman's breast tissue can also predict how she will respond to cancer treatment and whether her cancer will recur.

The denser a woman's breasts, the less fat they have, explains Diana Buist, Ph.D., of Group Health Center for Health Studies in Seattle. "If you have a dense breast, it's harder to see breast tumors on a mammogram."

Women with dense breasts are more likely to have abnormal mammograms, says Buist.

"Density on a mammogram is white, cancer on a mammogram is white," she says, which makes it more difficult to detect signs of cancer and can prompt reports of possible abnormalities.

According to Dr. Karla Kerlikowske, at the University of California, San Francisco, about 10 percent to 15 percent of women have low-density breasts, another 10 percent to 15 percent have very dense breasts, and the rest have breasts with a density somewhere in the middle.

But the average woman may not have a clue whether her breasts are dense, she says. For one thing, Dr. Kerlikowske adds, it is not as easy to measure density as it is to measure cholesterol.

"In the last 10 years, a lot of researchers have focused on how to measure it better, and what does it mean to have that density," she notes.

Dr. Kerlikowske was part of a research team that discovered that high breast density predicts local, but not distant, recurrence of cancer after a lumpectomy and radiation for invasive breast cancer.

Another group of researchers found that changes in breast density during treatment with tamoxifen, a drug used to lower breast cancer risk, help predict how well the drug is working.

Dr. Kerlikowske says that women with very high-density breasts have about a four-fold increase in risk compared with women who have very low-density breasts. And though density often decreases with age, especially after menopause, it remains a risk factor - and one which women cannot do much about, says Dr. Kerlikowske.

Always consult your physician for more information.