According to results recently released by the National Cancer Institute, the rate at which Evista® (raloxifene) reduces the risk of developing breast cancer is equal to that of Nolvadex® (tamoxifen) in postmenopausal women at a high risk of developing breast cancer within their lifetime. Raloxifene, however, is associated with fewer serious side effects than tamoxifen.
Breast cancer is accountable for approximately 40,000 deaths annually in the U.S. alone. The majority of women with breast cancer have cancer that is estrogen-receptor positive (ER-positive). This type of breast cancer is stimulated to grow by the female hormones estrogen and/or progesterone.
Women with ER-positive breast cancer are commonly treated with hormone therapy. This approach suppresses the formation of estrogen or blocks estrogen from stimulating cancer cells to grow.
Some postmenopausal women at a high risk of developing breast cancer can be treated with the anti-estrogen agent tamoxifen. Results from studies have indicated that tamoxifen can reduce the risk of developing breast cancer in these high-risk women by approximately 50%.
However, serious side effects associated with tamoxifen may prevent physicians from recommending its use as a preventive agent or may stop patients from taking tamoxifen for breast cancer prevention. These side effects include an increased risk of endometrial (uterine) cancer and the development of blood clots.
Tamoxifen is widely used in the treatment of ER-positive breast cancer; the drug’s benefits outweigh its risks in this setting.
Raloxifene is an agent that also reduces the stimulatory effects of estrogen on cancer growth. It is approved for the prevention and treatment of osteoporosis. However, due to the fact that it reduces estrogen’s effects on cells, researchers speculated that it may also be used as a preventive or therapeutic agent for ER-positive breast cancer.
Researchers conducted a clinical trial, referred to as the STAR trial, to directly compare raloxifene to tamoxifen in the prevention of breast cancer in women who were considered at a high risk of developing the disease. This trial included over 19,000 women who were considered high risk due to the following factors: a family history of breast cancer, personal medical history, age, age at first menstrual period, and age at first live birth. Women were followed for nearly 4 years.
- Raloxifene produced results equal to tamoxifen in reducing the risk of developing breast cancer among these women. Raloxifene, however, had fewer side effects than tamoxifen.
- Rates of breast cancer were reduced by approximately 50% in both groups of patients.
- Among women who had not had a hysterectomy (approximately half of the women), those treated with raloxifene had a 38% reduced rate of uterine cancer than those treated with tamoxifen.
- Women treated with raloxifene had a 29% reduced risk of developing blood clots compared to those treated with tamoxifen.
- Women treated with raloxifene had an approximately 20% reduced risk of developing cataracts compared to those treated with tamoxifen.
- Women treated with tamoxifen had fewer cases of lobular carcinoma in situ (LCIS) and ductal carcinoma in situ (DCIS)-conditions considered to be “pre-cancerous”-than those treated with raloxifene.
The researchers concluded that treatment with raloxifene appears to reduce the risk of developing breast cancer equally as well as tamoxifen among postmenopausal women who are considered to be at a high risk of developing the disease. However, raloxifene appears to have significantly fewer serious side effects than tamoxifen, which may ultimately make raloxifene a more favorable candidate for prevention of breast cancer.
Raloxifene is not approved for prevention or treatment of breast cancer. The researchers also caution that direct comparisons of raloxifene to aromatase inhibitors are necessary to ultimately determine the clinical benefit of raloxifene for prevention of breast cancer.
Reference: National Cancer Institute. Initial Results of the Study of Tamoxifen and Raloxifene (STAR) Released: Osteoporosis Drug Raloxifene Shown to be as Effective as Tamoxifen in Preventing Invasive Breast Cancer. Available at: http://www.cancer.gov/newscenter/pressreleases/STARresultsApr172006. Accessed April 2006.