Among postmenopausal women at increased risk of breast cancer, use of either tamoxifen (Nolvadex®) or raloxifene (Evista®) can substantially reduce the risk of breast cancer. The reduction in risk was somewhat greater with tamoxifen (50% versus 38% with raloxifene), but women treated with tamoxifen were also more likely to experience certain serious side effects. These results were published in Cancer Prevention Research.
Drugs that block the effects of estrogen have been shown to reduce the risk of breast cancer in women at high risk of the disease. Two drugs that have been approved for breast cancer risk reduction in certain groups of women are tamoxifen and raloxifene. Tamoxifen is approved for breast cancer risk reduction in women who are at high risk of the disease (including high-risk premenopausal women). Raloxifene—originally approved for the prevention and treatment of osteoporosis—is approved for breast cancer risk reduction in postmenopausal women with osteoporosis or postmenopausal women at high risk of breast cancer.
To directly compare raloxifene to tamoxifen in the prevention of breast cancer in high-risk women, researchers conducted a clinical trial known to as the STAR trial (The NSABP Study of Tamoxifen and Raloxifene [STAR] P-2 Trial). The study enrolled more than 19,000 postmenopausal women at increased risk of breast cancer. Women were assigned to receive either tamoxifen or raloxifene daily for five years. Study participants have now been followed for a median of 6.8 years.
Initial results from the trial indicated that raloxifene and tamoxifen were similarly effective at reducing the risk of invasive breast cancer—both drugs reduced risk by roughly 50%. Raloxifene appeared to be somewhat less effective, however, at reducing the risk of noninvasive breast cancers such as ductal carcinoma in situ (DCIS).
More recent, longer-term results indicate that as women in the study completed five years of the drugs and stopped taking them, tamoxifen continued to reduce the risk of invasive and noninvasive breast cancer by roughly 50% compared with a roughly 38% reduction in risk with raloxifene.
Study participants who took raloxifene had fewer serious side effects than study participants who took tamoxifen, both initially and after longer-term follow-up. Side effects that were less common in women treated with raloxifene than women treated with tamoxifen included uterine cancers, blood clots, and cataracts.
The results of this study demonstrate that both tamoxifen and raloxifene reduce the risk of breast cancer in postmenopausal women at increased risk of the disease. Women at elevated risk of breast cancer as a result of family history or other characteristics may wish to talk with their doctor about the risks and benefits of using one of these drugs to reduce breast cancer risk.
Reference: Vogel VG, Costantino JP, Wickerham DL et al. Update of the National Surgical Adjuvant Breast and Bowel Project Study of Tamoxifen and Raloxifene (STAR) P-2 Trial: Preventing Breast Cancer. Cancer Prevention Research [early online publication]. April 19, 2010.