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Raloxifene Shows More Promise in Preventing Breast Cancer (dateline February 5, 2002)


Results of another study have shown that the osteoporosis drug raloxifene (brand name, Evista) may help prevent breast cancer in women at high risk for the disease. In this latest study, researchers found that raloxifene reduced breast cancer risk in women who had naturally high levels of estrogen in their blood—a factor that has been linked to higher-than-average breast cancer risk. If the results of this study are confirmed in another study that is currently underway, researchers expect the U.S. Food and Drug Administration (FDA) to approve the use of raloxifene in women at high breast cancer risk within three years.

Raloxifene belongs to the same class of drugs (know as SERMs, selective estrogen receptor modulators) as tamoxifen (brand name, Nolvadex). Tamoxifen is the only drug currently FDA-approved to help prevent breast cancer in high risk women. In addition to preventing and treating osteoporosis (a degenerative bone disease), researchers believe that raloxifene may also prevent breast cancer, similarly to the way tamoxifen does. Researchers also believe that raloxifene may be associated with fewer side effects than tamoxifen (such as hot flashes or the slight increased risk of endometrial cancer---cancer of the uterine lining).

To conduct their study of raloxifene, Steven R. Cummings, MD of the University of California, San Francisco, and his colleagues analyzed 7290 post-menopausal women aged 80 years or younger with osteoporosis (average age: 67). The women had been enrolled in an osteoporosis study called "Analysis of the Multiple Outcomes of Raloxifene Evaluation," which had been conducted between 1994 and 1999 at 180 community settings and medical practices in 25 countries. None of the women in the study had a history of breast cancer, nor had any used estrogen replacement therapy.

Each of the women in the study was given either raloxifene (60 or 120 milligrams) or a placebo (inactive pill) for four years. A baseline analysis of the women’s blood was performed to determine their levels of estrogen (specifically, one type of estrogen called estradiol).

Dr. Cummings and his colleagues found that among the women who took the placebo, those with high estradiol levels were 6.8 times more likely to develop breast cancer over four years compared with women with normal estradiol levels who took the placebo. Interestingly, the researchers found that among the women with high estradiol levels who took raloxifene, the drug lowered their risk of breast cancer by 76% over four years. Raloxifene did not have any effect on breast cancer risk among women with normal estradiol levels.

Thus, Dr. Cummings and his colleagues conclude that measuring a woman’s blood estrogen levels helps determine whether she is likely to lower her risk of breast cancer by taking raloxifene. Furthermore, the researchers say that if their study is confirmed with further research, testing and treating women with high estradiol levels could significantly reduce the incidence of breast cancer among post-menopausal women.

Researchers believe that raloxifene prevents breast cancer in women with high estradiol levels by competing with estradiol and blocking it from receptors in breast tissue cells. Without estradiol, breast cells are less likely to develop into cancer.

A large clinical trial called STAR (Study of Tamoxifen and Raloxifene) is currently underway that is investigating the long-term safety and effectiveness of both tamoxifen and raloxifene in helping to prevent breast cancer in women at high risk for the disease. The results of STAR will help researchers better understand the benefits (and limitations) of both drugs. In the meantime, raloxifene is not approved to prevent breast cancer in women outside of a clinical trial setting.

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