At Risk: Isolating the Factors Involved in Breast Cancer

By NICHOLAS BAKALAR
Breast density and high levels of circulating sex hormones are independent risk factors for breast cancer in postmenopausal women, a new study finds.
It is known that women who have denser breasts, breasts that have more connective tissue than fat, are at higher risk for breast cancer. It is also known that higher levels of circulating sex hormones put women at increased risk. But because the two often occur together, it has been unclear whether each is a risk by itself.
Researchers studied 253 women who had breast cancer, comparing their breast density and levels of sex hormones with 520 women without the disease. After controlling for other factors, they found that when breast density was not considered, women in the highest quarter in circulating sex hormones had twice the risk of developing breast cancer as those in the lowest one-quarter.
They also found that women in the highest one-quarter in density had four times the risk of those in the lowest quarter, without considering levels of sex hormones.
Women with both the highest hormones and densest breasts had up to six times the risk.
“Having dense breasts or high hormone levels doesn’t mean you’re going to get breast cancer,” said Celia Byrne, a co-author of the study and an assistant professor of epidemiology at Georgetown. “But screening is important, and maintaining lower weight can help keep hormone levels lower.”
The report, in the Aug. 1 issue of The Journal of the National Cancer Institute, is based on a nine-year prospective study.