LOS ANGELES -- Researchers at the University of California San Francisco report that a novel hormone therapy drug reduces the risk of breast cancer in women by 70 percent.
"Our findings are very exciting because they show that it may be possible to prevent breast cancer in postmenopausal women who have no prior history of the disease," says Steven Cummings, MD, UCSF professor of medicine and epidemiology and lead author of the study.
Cummings presented his findings today (May 18) at the annual meeting of the American Society of Clinical Oncology.
UCSF researchers found that the osteoporosis prevention drug, raloxifene, drastically reduced the risk of breast cancer in postmenopausal women without indicating an increased risk of endometrial, or uterine cancer. Other drugs in raloxifene's class, including tamoxifen, have been shown to increase the risk of endometrial cancer in women.
Although tamoxifen was recently reported to reduce the risk of breast cancer in women who are at high risk of the disease by 45 percent, it also showed an increased risk of endometrial cancer. Of the 13,388 women who participated in the tamoxifen study, 33 of those who received the drug developed endometrial cancer, compared to 14 of the women assigned to placebo. Raloxifene and tamoxifen belong to a class of drugs called selective estrogen receptor modulators (SERMS), which block the actions of estrogen in some tissues, such as the breasts, and mimic estrogen in other tissues, such as the bones.
"During the clinical trials of raloxifene, we saw twice as many cases of breast cancer develop among women taking placebo compared to those taking raloxifene," Cummings says.
After an average of 33 months, 32 cases of breast cancer developed in the women who participated in the study. While 21 or .82 percent of the women who were given placebo developed breast cancer, only 11 or .21 percent of those assigned to raloxifene developed the disease. However, like tamoxifen and estrogen, Cummings noted that raloxifene does increase a woman's risk of developing blood clots.
He added that raloxifene also reduced the risk of estrogen-receptor positive breast cancer in participating women by 87 percent; and did not affect the risk of estrogen-receptor negative cancer.
Approximately two-thirds of breast cancers in postmenopausal women are estrogen-receptor positive. These cancer tumors' cells contain a protein, or receptor, that responds to estrogen, stimulating tissue growth in a woman's breasts, which can increase her risk of breast cancer.
During the UCSF-led study, 7,705 postmenopausal women up to age 80 years (mean age 66.5 years) who have osteoporosis and no history of breast or endometrial cancer were randomly assigned to receive either 60 or 120 milligrams per day of raloxifene or a matching dose of placebo. Twice as many women were given raloxifene as those in the control group who received placebo. Excluding skin cancer, breast cancer is the most common form of cancer among women, accounting for one out of every three cancer diagnoses in the United States. Approximately one in nine women will develop breast cancer during her lifetime, and it is estimated that the disease will strike 178,000 women in the US this year, and kill 43,500.
Because breast cancer can take five or more years to become detectable, Cummings said that the study will continue for at least another four years to determine the long-term benefits of raloxifene in women. He added that the women who are participating in the clinical trials are making enormous contributions to the fight against breast cancer.
"If we continue to see positive results from the study, as we expect, women who are concerned about breast cancer should consult their doctors about whether raloxifene is a treatment they should consider," Cummings says.
Raloxifene is unique to other SERMS, such as tamoxifen, because it has a positive, estrogen-like effect on a woman's bones and cholestoral levels, yet does not mimic estrogen's adverse effects on her breasts and uterus.
Estrogen acts by binding to structures called receptors in various target tissue cells, which then stimulate different responses. The hormone can cause tissue growth in a woman's breasts and uterine lining, and over time, may increase her risk of breast or endometrial cancer.
At the same time, however, estrogen has been proven to significantly reduce a woman's risk of osteoporosis and may reduce her risk of heart disease. Raloxifene was approved for the prevention of osteoporosis by the Food and Drug Administration in December 1997. It is marketed as Vista by Eli Lilly and Co., the sponsors of the clinical trials of the treatment as a method of preventing breast cancer.
Note To The Media:
To interview Steven Cummings, M.D., please contact Abby Sinnott in UCSF news services at (415) 885-7277.