Dense breast tissue can obscure abnormal growths, making it harder for physicians to analyze mammograms. According to two new studies, hormone-replacement therapy that includes estrogen can make breast tissue more dense, while the use of raloxifene, an estrogen-replacement drug, does not.
Researchers at the Group Health Cooperative of Puget Sound in Seattle analyzed pairs of density readings, taken 2 years apart, from 5,212 postmenopausal women. Those who had started taking estrogen and progesterone between the mammograms were more than twice as likely to show a significant rise in density as were women not using hormone therapy.
Those who stopped taking hormones between mammograms were nearly twice as likely as nonusers to show a drop in density. The results appear in the Jan. 10, 2001 Journal of the American Medical Association.
“Our study suggests that increases in breast density associated with hormone-replacement therapy are potentially reversible,” says study coauthor Carolyn M. Rutter, a biostatistician at Group Health Cooperative. However, since the therapy doesn’t cause breast density to rise in every woman, Rutter says, women and their physicians should weigh the pros and cons of stopping therapy.
Another option might be to replace estrogen with the drug raloxifene. Researchers at Georgetown University Medical Center in Washington, D.C., gave 168 women raloxifene, estrogen, or an inert substitute over 2 years. The raloxifene group showed a decrease in breast density of at least 1.5 percent. Those getting a placebo showed a slightly smaller decrease, one that was typical for postmenopausal women. Those receiving estrogen registered a density increase of 1.4 percent on average, the scientists report in the Jan. 2, 2001 Journal of the National Cancer Institute.
This study adds to evidence that raloxifene mimics beneficial effects of estrogen but not deleterious ones, says study coauthor Matthew Freedman, a radiologist at Georgetown. Both hormones help to maintain bone mass, but raloxifene doesn’t add to breast density in the process, he says.