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.