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An international research team says it has conclusive proof that the drug tamoxifen can reduce the likelihood that women at high risk of
breast cancer will develop the disease. The researchers analyzed results of several
tamoxifen clinical trials to reach their conclusion. Though the results are positive and
tamoxifen is already approved by the Food and Drug Administration (FDA) to prevent breast
cancer in high-risk women in the United States, the researchers say the next step is to
reduce the potentially harmful side effects of tamoxifen before it should become widely
used to prevent breast cancer.
Tamoxifen (brand name, Nolvadex) is an "anti-estrogen" drug that has been
used for over 20 years to treat breast cancer. Many breast cancer cells depend on the
hormone estrogen to grow and survive. Tamoxifen works by competing with estrogen to bind
to estrogen receptors on breast cancer cells. By blocking estrogen from these cells, the
cancer cells are essentially "starved." Researchers are also investigating
whether tamoxifen can be effective in women whose cancers do not have estrogen-receptors
(so-called estrogen receptor-negative, or ER-negative, cancers).
In 1998, the U.S. FDA approved tamoxifen to help prevent breast cancer in women at
high-risk for the disease (based on family history, etc.). This decision came after a
large clinical trial (the National Adjuvant Breast and Bowel Project’s Breast Cancer
Prevention Trial) found that tamoxifen could reduce the risk of breast cancer by
approximately 50% compared to an inactive pill (placebo). In fact, the trial was stopped
early so women who were being given the placebo could also receive the benefits of
tamoxifen.
In the latest research on tamoxifen, Professor Jack Cuzick, PhD, Senior Researcher at
Cancer Research UK, a British charity, and colleagues analyzed the results of five breast
cancer prevention trials in which tamoxifen and a similar drug, raloxifene (brand name, Evista) were given.
"In our analysis we combined all the available evidence from studies using
tamoxifen for breast cancer prevention – collectively involving over 40,000 women
– and it is clear to us now that the drug can reduce the chance of high-risk women
developing the disease," said Professor Jack Cuzick, in a Cancer Research UK
statement. Specifically, Professor Cuzick and colleagues found a 38% reduction in the
likelihood of developing breast cancer among women who had taken tamoxifen.
However, the researchers noted that the side effects of tamoxifen limit its
accessibility. "The evidence to date clearly shows that tamoxifen can reduce the risk
of breast cancers stimulated by the hormone estrogen," said Professor Cuzick.
"However, it is crucial that we follow all the trials to their conclusions and find
ways to reduce the side-effects of tamoxifen before we can recommend that high-risk women
take the drug to prevent breast cancer."
The most common side effect of tamoxifen is a higher occurrence of hot flashes. Other
side effects include irregular menstrual cycles, unusual vaginal discharge or bleeding,
and irritation of skin around the 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
The risks of these complications are generally small and are discussed in detail at http://www.imaginis.com/breasthealth/side_effects.asp.
Professor Cuzick suggested that possible ways to reduce these side effects include
lowering the dose of tamoxifen or adding a small dose of aspirin.
The team’s research also showed that the drug raloxifene appears promising in
preventing breast cancer, but the final results of a large clinical trial called STAR, the Study of Tamoxifen and Raloxifene, are needed. STAR involves
22,000 American women at high risk of developing breast cancer. Other drugs, such as anastrozole (brand name, Armidex) may also be
effective at preventing breast cancer.
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