News

An osteoporosis drug has been found to reduce the incidence of invasive breast cancer in high-risk, post-menopausal women as effectively as tamoxifen, the medication considered the gold standard for warding off the disease over the last two decades.

In a head-to-head study, both tamoxifen and raloxifene were found to reduce the risk of invasive breast cancer by almost 50 per cent compared with placebo — but raloxifene had far fewer serious side-effects.

“This is good news for women,” Dr. Leslie Ford of the U.S. National Cancer Institute, told a teleconference Monday to announce the results of the five-year Study of Tamoxifen and Raloxifene (STAR). “We think this will give women a real choice.”

Almost 20,000 post-menopausal women from the United States, Canada and Puerto Rico, all of whom were at increased risk of breast cancer, took part in the STAR study, one of the largest breast cancer prevention trials ever undertaken.

During the study, about half the women were randomly assigned to receive tamoxifen, while the other half were given raloxifene, a drug approved for widespread use to prevent and treat osteoporosis.

Previous studies had suggested raloxifene, sold under the brand name Evista by Eli Lilly & Co., could also prevent breast cancer in some women, although it is not approved for that use.

In 1998, tamoxifen was shown in the landmark Breast Cancer Prevention Trial to reduce incidence of the disease by 49 per cent compared with placebo in women at increased risk. The drug, which works by interfering with the female hormone estrogen, has been used to prevent breast cancer in high-risk women since the late 1990s.

Raloxifene, which also works by inhibiting the potentially cancer-causing effects of estrogen, was found to be equally effective in preventing invasive breast cancer, which is characterized by its ability to spread into other tissues.

Both drugs can cause such serious side-effects as uterine cancer (except in women who have had hysterectomies), blood clots in the legs or lungs, and stroke.

While the threat of stroke was about equal for both drugs, the incidence of uterine cancer was 38 per cent lower with raloxifene than tamoxifen, 36 per cent lower for potentially life-threatening blood clots to the lungs, and 26 per cent lower for leg clots (deep vein thrombosis).

Post-menopausal women can be at elevated risk for invasive breast cancer depending on a number of factors: age, number of first-degree relatives (mother, daughters or sisters) diagnosed with breast cancer; whether a woman has had children and her age at first delivery; and the age of the first menstrual period.

Results from the new study will not mean a change for pre-menopausal women with a high risk of breast cancer, as there is no data showing whether raloxifene is safe for that group, researchers said.