Osteoporosis Drug, Raloxifene, Shows Promise in Preventing Breast Cancer (dateline April 30, 2006)
Initial results of a large study show that the osteoporosis drug raloxifene (brand name, Evista) may be as effective at preventing breast cancer as the standard drug, tamoxifen, but with fewer side effects. In the STAR (Study of Tamoxifen and Raloxifene) study, both drugs reduced the risk of breast cancer by about 50% in post-menopausal women who had a high risk of developing the disease. However, after an average of four years, women who took raloxifene had developed about 36% fewer uterine cancers and 29% fewer blood clots than the women who took tamoxifen.
"This optimistic news from STAR is a significant step in breast cancer prevention," said John E. Niederhuber, MD, currently providing leadership at the National Cancer Institute (NCI), in an NCI news release. "These results, once again, demonstrate the critical importance of clinical trials in our efforts to establish evidence-based practices."
The STAR trial is conducted by researchers of the National Surgical Adjuvant Breast and Bowel Project (NSABP). The STAR trial is one of the largest studies on breast cancer prevention ever undertaken. It is supported by the National Cancer Institute (NCI), Eli Lilly and Company (who markets Evista/raloxifene for the treatment of osteoporosis), and Zeneca Pharmaceuticals.
To conduct the study, researchers enrolled 19,747 post-menopausal women who were at least 35 years old, and had an increased risk of breast cancer as determined by their age, family history of breast cancer, personal medical history, age at first menstrual period, and age at first live birth. Participants were randomly assigned to receive either raloxifene or of tamoxifen daily for five years.
The results of the STAR trial showed that the number of women who developed invasive breast cancers was statistically equal regardless of whether women took tamoxifen or raloxifene. Among the 9,745 women who took raloxifene, 167 developed invasive breast cancer, compared to 163 of 9,726 women who took tamoxifen.
"In 1998, the landmark Breast Cancer Prevention Trial showed that tamoxifen could reduce the risk of invasive breast cancer in pre-menopausal and post-menopausal women by nearly 50 percent," said Norman Wolmark, MD, NSABP chairman, in an NCI news release. "Today, we can tell you that for postmenopausal women at increased risk of breast cancer, raloxifene is just as effective, without some of the serious side effects known to occur with tamoxifen."
The STAR trial results showed that women who took raloxifene had 29% fewer deep vein thromboses (blood clots in a major vein) and pulmonary embolisms (blood clots in the lung) than women who took tamoxifen. More than half of the women who participated in the STAR trial had had their uteruses removed (hysterectomy). Among the women who had uteruses, there were 36% fewer uterine cancers among those who took raloxifene compared to those who took tamoxifen.
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.
While tamoxifen and raloxifene may fight estrogen in breast cancer cells, they also mimic the positive effects of estrogen in other body systems. Post-menopausal women who take tamoxifen may decrease their risk of heart disease or osteoporosis (a degenerative bone disease) without having to use hormone replacement therapy (HRT). Raloxifene is commonly prescribed help prevent and treat osteoporosis. It has been shown to help build new bone and reduce the risk of fractures.
"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, MD, associate director for clinical research in NCI's Division of Cancer Prevention, in an NCI news release. "For many women, raloxifene's benefits will outweigh its risks in a way that tamoxifen's benefits do not."
Raloxifene was approved in December 1997 by the FDA to prevent osteoporosis and has been in clinical trials for over five years. Tamoxifen has been approved by the FDA to treat women with breast cancer for more than two decades. Raloxifene (Evista) is currently FDA approved and labeled only for use in preventing/treating osteoporosis in post-menopausal women.
Additional STAR trial results will be presented at the 42nd annual meeting of the American Society for Clinical Oncology (ASCO) from June 2-6, 2006, in Atlanta, Georgia.