Raloxifene, a drug frequently prescribed to prevent and treat osteoporosis, has been shown by a large, national clinical trial to work as well as the breast cancer drug tamoxifen to reduce the risk of invasive breast cancer for postmenopausal women who have a higher-than-normal risk for the disease.
This could be good news for women who may not want to take tamoxifen because it can raise the odds of developing uterine cancer, blood clots, strokes and cataracts.
Researchers at the Siteman Cancer Center participated in the two-drug study, called the STAR trial (Study of Tamoxifen and Raloxifene). The STAR trial, one of the largest breast cancer prevention studies ever conducted, enrolled nearly 20,000 women and was coordinated by the National Surgical Adjuvant Breast and Bowel Project and sponsored by the National Cancer Institute (NCI). Women who participated in the STAR trial were postmenopausal, at least 35 years old and had an increased risk of breast cancer.
“Earlier studies found that postmenopausal women who took raloxifene for osteoporosis lowered their risk of breast cancer,” said Antonella Rastelli, M.D., principal investigator for the School of Medicine STAR trial center and instructor in medicine. “Because taking tamoxifen carries certain serious risks, it was important to determine if raloxifene, which has fewer risks, could be an effective substitute to reduce the risk of breast cancer in high-risk patients.”
Tamoxifen has been used for more than 20 years to treat patients with advanced breast cancer. A study released in 1998 showed that it also had a preventative capacity. High-risk women without cancer who took tamoxifen reduced their chances of developing both invasive and noninvasive breast cancers by nearly 50 percent.
In contrast to tamoxifen, raloxifene does not appear to raise the risk of uterine cancer, strokes or cataracts, although some studies suggest it does slightly increase a patient’s risk of stroke.
The STAR trial demonstrated that raloxifene, like tamoxifen, reduced the risk of invasive breast cancer by 50 percent, and women who took raloxifene had 36 percent fewer uterine cancers and 29 percent fewer blood clots than women assigned to take tamoxifen.
In the STAR trial, women taking either drug had an equivalent number of strokes. Tamoxifen demonstrated superior ability to reduce the incidence of noninvasive breast cancers.
“Although no drugs are without side effects, tamoxifen and raloxifene are vital options for women who are at increased risk of breast cancer and want to take action,” said Leslie Ford, M.D., associate director for clinical research in NCI’s Division of Cancer Prevention. “For many women, raloxifene’s benefits will outweigh its risks in a way that tamoxifen’s benefits do not.”
Tamoxifen and raloxifene are synthetic estrogen mimics that have different effects on estrogen receptors in different parts of the body, producing estrogenic effects in some sites and acting like anti-estrogens in other places. While the two drugs act slightly differently in various tissues, both tamoxifen and raloxifene appear to function like estrogen in bone — maintaining bone strength and increasing bone density — but they compete with estrogen in breast tissue to potentially lessen the likelihood of estrogen-induced breast tumors.