The Women's Health Resource. On the web since 1997.

Promising Research Shows Fewer Side Effects of Breast Cancer Prevention Drug, Raloxifene, Compared to Tamoxifen

Results from an ongoing study examining two drugs to prevent breast cancer found that the drug raloxifene (Evista) was as almost effective as the standard drug tamoxifen (Nolvadex) and also produced fewer side effects. Earlier results of the study had shown that raloxifene was as effective as tamoxifen in reducing non-invasive breast cancer in post-menopausal women at high risk of developing the disease. For both drugs, women experienced a 50 percent reduction in breast cancer risk after 4 years. These latest results show that tamoxifen continues to reduce risk for both invasive and non-invasive breast cancer by about 50 percent after 5 years of drug use, and raloxifene reduces risk for invasive and non-invasive breast cancer by about 38 percent.

The National Surgical Adjuvant Breast and Bowel Project (NSABP) is leading the STAR clinical trial - one of the largest trials of on breast cancer prevention ever undertaken. STAR, or Study of Tamoxifen and Raloxifene, is investigating whether the drugs tamoxifen (brand name, Nolvadex) and raloxifene (Evista), help prevent breast cancer in women at high risk for disease. Both tamoxifen and raloxifene are "anti-estrogens." Anti-estrogens work by competing with estrogen to bind to estrogen receptors in breast cancer cells. By blocking estrogen in the breast, tamoxifen and raloxifene may slow the growth and reproduction of breast cancer cells

In April 2006, researchers announced the initial results of STAR, which showed that raloxifene may be as effective as tamoxifen at preventing breast cancer in women at high risk for the disease. Specifically, those results showed that women who were given raloxifene reduced their risk of breast cancer by 50%. In addition, raloxifene may have fewer potentially serious side effects than tamoxifen. After an average of four years on raloxifene, women in the study developed about 36% fewer uterine cancers and 29% fewer blood clots than the women who took tamoxifen.

These latest results show that raloxifene is nearly as effective at preventing invasive breast cancer in high-risk women and produces fewer side effects. Specifically, the results show that after taking the drug for 5 years then stopping, raloxifene retained 76% of the effectiveness of tamoxifen in preventing invasive disease and grew closer to tamoxifen in preventing noninvasive disease while producing fewer side effects such as bone fractures, blood clots, or cataracts.

Tamoxifen has been shown to reduce the incidence of noninvasive breast cancers—specifically lobular carcinoma in situ (LCIS) and ductal carcinoma in situ (DCIS) by 50%. The latest study results show that raloxifene reduces the risk of non-invasive breast cancer by about 38 percent compared to tamoxifen's 50% reduction rate.

When deciding between tamoxifen and raloxifene, the National Cancer Institute advises the following: Postmenopausal women who are at increased risk of breast cancer should consider taking either raloxifene or tamoxifen to reduce their risk. As with any medical procedure or intervention, the decision to take one of these drugs is an individual one in which the benefits and risks of therapy must be considered. The balance of these benefits and risks will vary depending on a woman's personal health history and how she weighs the benefits and risks. Even if a woman is at increased risk of breast cancer, raloxifene or tamoxifen therapy may not be right for her. Women who are considering breast cancer prevention therapy should talk with their health care provider.

Additional Resources and References