CHICAGO (AP) -- Medical researchers have found a dramatic drop in the risk of breast cancer for women who take an estrogen substitute prescribed to prevent brittle bones.
The three-year study of 7,705 women found a 76 percent lower risk of breast cancer among post-menopausal women taking raloxifene compared with those given a placebo. The report was published in today's Journal of the American Medical Association."It's a very exciting beginning," said lead researcher Dr. Steven Cummings, a professor of medicine at the University of California at San Francisco. "But we've only had 3 1/2 to 4 1/2 years of experience with this. I think women should be cautious about any medications used for prevention."
Deborah Collyar -- a patient advocate from California and a breast cancer survivor who was not involved in the study -- agreed caution is needed.
"There are no magic bullets," said Collyar, president of Patient Advocates in Research. "When you look at the risk reduction, 76 percent sounds like a tremendous amount, and it is. But you have to look at what the absolute risk of those women was in the first place."
Raloxifene is part of a new generation of drugs scientists hope will mimic the good effects of estrogen -- stronger bones and a lower risk of heart disease -- while inhibiting the possible harmful effects, which may include promoting breast and uterine cancer.
Raloxifene, the first so-called "designer estrogen," was approved in 1997 by the Food and Drug Administration for preventing osteoporosis. It has not been shown to affect heart disease.
It is marketed under the name Evista by Eli Lilly and Co., which paid for the study.
Many women are afraid to use estrogen because of conflicting evidence on whether it promotes breast cancer. However, a study released last week on 37,000 women suggested that hormones do not increase the risk of breast cancer, except for some uncommon and highly curable forms of the disease.
Raloxifene isn't risk-free. It increases the chances of serious blood clots.
In Cummings' study, 5,129 post-menopausal women younger than 81 received raloxifene daily, while 2,576 got a dummy pill. Thirteen cases of breast cancer were diagnosed among the women taking raloxifene; 27 cases were found among those taking the placebo.
Women taking raloxifene had a 90 percent lower risk of a type of cancer called estrogen-receptor positive breast cancer.
However, raloxifene had almost no effect on estrogen-receptor negative breast cancer, one of the hardest forms of the disease to treat. It is most commonly developed by younger women and those with a genetic predisposition to the disease.
Dr. Janet Wolter of Rush-Presbyterian-St. Luke's Medical Center in Chicago said she is encouraged by the findings and hopes more research will determine whether the breast cancer drug tamoxifen or raloxifene is more effective and produces fewer side effects.
An accompanying editorial cautioned that raloxifene cannot yet be considered suitable for most women.
"Its contributions to knowledge intensify the anticipation of finding something even better on this new frontier," wrote Drs. Adele Franks of the Prudential Center for Health Care Research in Atlanta and Karen Steinberg of the U.S. Centers for Disease Control and Prevention.