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In recent studies, several drugs have shown promise in helping to protect women against
breast cancer. In 1998, the National Surgical Adjuvant Breast and Bowel Project’s
Breast Cancer Prevention Trial found that the drug tamoxifen
reduced the risk of breast cancer in women who were at high risk of
the disease by up to 49%. Both tamoxifen and a newer drug raloxifene (brand name, Evista)
are "anti-estrogens." Anti-estrogens work by competing with estrogen to bind and
block 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.
However, tamoxifen has been associated with side effects, such as hot flashes, and more
seriously, blood clots and stroke. Tamoxifen has also been shown to slightly increase the
risk of uterine cancer, researchers to seek alternative drugs with fewer side effects.
While raloxifene, like tamoxifen, also increases the risk of deep vein thrombosis (blood
clots in the deep veins of the leg) and pulmonary embolism (blood clots in the lungs),
unlike tamoxifen, it does not appear to increase the risk of uterine cancer. Raloxifene
has also been shown to help prevent osteoporosis and is approved by the U.S. Food and Drug
Administration (FDA) for this use.
In 1999, researchers reported the results of the Multiple Outcomes of Raloxifene
Evaluation (MORE) clinical trial. They found that raloxifene reduced verebretal bone
fractures in women with osteoporosis by 35%. They also discovered that raloxifene reduced
the risk of breast cancer by 72% after four years of use.
In the recently published results of the Continuing Outcomes Relevant to Evista (CORE)
clinical trial, Dr. Silvana Martino, of the Cancer Institute Medical Group in Santa
Monica, California, and colleagues reported that continued treatment with raloxifene
reduces breast cancer risk post-menopausal women with osteoporosis. The researchers found
a 59% decreased risk of breast cancer each year among women treated with up to 4
additional years of raloxifene.
In an editorial in the December 1, 2004 issue of the Journal of the National Cancer
Institute, Dr. Powel Brown and colleagues from Breast Center at Baylor College of
Medicine in Houston, Texas acknowledge the promise of the CORE study results. However,
they also cite several issues with the study’s design which complicate interpretation
of the results. For example, women who developed breast cancer or experienced a serious
adverse event during the long time period between the end of the MORE trial and the
beginning of the CORE trial were excluded from CORE, which lowers the incidence of breast
cancer in the CORE group.
At this time, Dr. Brown and his colleagues pose five questions that remain to be
answered with regard to breast cancer prevention:
- What is the most effective drug to use for breast cancer prevention?
- Which drug is safest?
- Who should be treated with preventive therapy?
- How are the risks and benefits of preventive therapy best assessed?
- What is the optimal duration of preventive therapy?
A large clinical trial called STAR (Study of Tamoxifen and Raloxifene) is currently
underway that may help to answer these questions. STAR is examining and comparing the
benefits and risks of both tamoxifen and raloxifene in preventing breast cancer among
women at high risk for the disease. Click here to learn more about the
STAR trial.
In addition, the results of a European study called the International Breast Cancer
Intervention Study 2 trial may help determine whether the drug anastrazole (brand name, Arimidex), an aromatase
inhibitor, is effective in preventing breast cancer in high-risk post-menopausal women.
Until the results of these studies are known, women are encouraged to talk to their
physicians about the best course of prevention. For most women, this consists of monthly breast self-exams, regular clinical
breast exams, and yearly mammograms beginning at age 40.
Women at high risk of breast cancer as determined by family history or genetic testing may
wish to consider alternative methods, including more frequent screening or in some cases,
preventive breast removal (prophylactic mastectomy).
Additional Resources and References
Updated: September 12, 2007
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