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.
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 for use in preventing/treating osteoporosis in post-menopausal women.
As with all drug treatments, the side effects of tamoxifen and raloxifene vary from individual to individual. The most common side effect of tamoxifen and raloxifene is a higher occurrence of hot flashes. Other side effects of tamoxifen include irregular menstrual cycles, unusual vaginal discharge or bleeding, and irritation of skin around the vagina. Tamoxifen does not cause menopause in pre-menopausal women, though its side effects may mimic menopausal symptoms. For most young women who take tamoxifen, the ovaries continue to act normally and produce estrogen in the same or slightly increased amounts. In fact, some studies have suggested that tamoxifen may make pre-menopausal women more fertile.
Side effects of tamoxifen include:
- Hot flashes
- Irregular menstrual cycles
- Unusual vaginal discharge or bleeding
- Irritation of skin around vagina
Tamoxifen also increases a woman's chances of developing serious health problems including:
- endometrial cancer (cancer of the lining of the uterus)
- deep vein thrombosis (blood clots in large veins, particularly in the legs)
- pulmonary embolism (blood clot in the lung)
- possibly stroke
Because endometrial cancer is a side effect of tamoxifen, women with uterine problems are not usually candidates for tamoxifen treatment. In addition, pregnant women should not use tamoxifen because animal studies reveal that the drug may cause serious harm to the growing fetus. Women with a personal history of severe blood clotting or cataracts should also avoid tamoxifen.
Women should not take tamoxifen if:
- they are pregnant
- have a history of uterine problems
- have a history of blood clots
- have a history of cataracts
Raloxifene can cause serious side effects including blood clots in the legs and lungs, and death due to stroke. Women with current or prior blood clots in the legs, lungs, or eyes should not take Evista. Other potential side effects include:
- hot flashes
- leg cramps
- swelling of the legs and feet
- flu-like symptoms
- joint pain
- sweating
The FDA cautions that raloxifene should not be taken by pre-menopausal women and women who are or may become pregnant because it may cause harm to the unborn baby. In addition, ralxofene should not be taken with cholestyramine (a drug used to lower cholesterol levels) or estrogens.
- For information on the National Adjuvant Breast and Bowel Project (NSABP), please visit http://www.imaginis.com/breasthealth/star/nsabp_info.asp
- For NSABP information on STAR and how to enroll, please visit http://www.nsabp.pitt.edu/
- To learn more about tamoxifen, please visit http://www.imaginis.com/breasthealth/tamoxifen.asp
- For NSABP information on STAR, please visit http://www.nsabp.pitt.edu/
- To learn more about raloxifene, please visit http://www.imaginis.com/osteoporosis/osteo_treatment.asp#raloxifene
- The April 30, 2006 Imaginis.com article, "Osteoporosis Drug, Raloxifene, Shows Promise in Preventing Breast Cancer," is available at http://www.imaginis.com/breasthealth/news/news4.30.06.asp
Updated: November 12, 2007
