Skip to content
My WebMD Sign In, Sign Up

Breast Cancer Health Center

Font Size

Tamoxifen as Prevention Questioned

Popular Breast Cancer Drug May Not Lengthen Life for Most
By
WebMD Health News
Reviewed by Louise Chang, MD

July 24, 2006 - Most women with an elevated risk for breast cancer will not live longer if they take the cancer prevention drug tamoxifen, a new study shows.

Researchers concluded only very high-risk women benefit in terms of life expectancy when they take the drug for prevention.

They calculated that women at the lower end of the high-risk scale would spend a whopping $1.3 million per year of life added if they purchased tamoxifen in the United States. In Canada, where the drug sells for much less, the cost per year of life saved was estimated to be about one-tenth that amount.

The researchers used a computer-generated model to predict life expectancies for a hypothetical group of women at high risk for breast cancer who did and did not take tamoxifen to lower their risk.

Researcher Joy Melnikow, MD, of the University of California-Davis, tells WebMD the model showed tamoxifen had less of an impact on mortality (death) than expected because it does not protect against the most deadly breast cancers -- those not fueled by estrogen.

Tamoxifen is a selective estrogen receptor modulator (SERM) drug that works as an antiestrogen. Estrogen promotes the growth of most breast cancer cells. So the drug targets estrogen receptors on the cancer cells, which blocks estrogen from them. It is widely used as a breast cancer treatment, and was approved in 1998 by the FDA to lower breast cancer risk in women at high risk.

"The fact that the cancers prevented by tamoxifen and (the SERM) raloxifene are easier to treat and have a better prognosis really hasn't been considered before," Melnikow says.

All in the Numbers

Tamoxifen was approved for prevention, based on findings from a landmark government study in which high-risk women who took the drug for five years had a 49% reduction in breast cancer incidence, compared with women who did not.

High risk was defined as having at least a 1.67% risk of developing breast cancer within five years, based on a standardized risk assessment tool known as the GAIL model.

In the latest study, however, researchers estimated that mortality rates would actually increase slightly in women with this level of risk when the impact of estrogen-receptor negative breast cancers was considered. Estrogen-receptor negative breast cancers are not fueled by estrogen and therefore not helped with tamoxifen.

Meanwhile, tamoxifen use is associated with an increased risk for uterine cancer. Tamoxifen is also associated with increased risk for serious blood clots that can be life-threatening, and for cataracts.

The researchers concluded it would take a breast cancer risk of greater than 3% to derive a potential mortality benefit from tamoxifen.

The model did show a mortality benefit for tamoxifen users at all levels of risk if the women had had hysterectomies. The increased risk of uterine cancer from using tamoxifen does not exist for these women.

"The projected benefits of tamoxifen for women at or near the threshold risk for breast cancer of 1.67% are very small or nonexistent," Melnikow and colleagues conclude in the Sept. 1 issue of the American Cancer Society journal Cancer.

Melnikow tells WebMD that women with a five-year breast cancer risk of less than 2.5% or 3% should probably not take tamoxifen, especially if they have not had hysterectomies.

Today on WebMD

Breast Cancer Overview
From self-exams and biopsies to reconstruction, we’ve got you covered.
Dealing with breast cancer
Get answers to your questions.
 
woman having mammogram
Experts don’t agree on all fronts, but you can be your own advocate.
woman undergoing breast cancer test
Many women worry. But the truth? Most abnormalities aren’t breast cancer.
 
Breast Cancer Treatments Improving
VIDEO
Resolved To Quit Smoking
SLIDESHOW
 
Woman getting mammogram
Article
Screening Tests for Women
SLIDESHOW
 
ovarian cancer overview slideshow
SLIDESHOW
serious woman
Article
 
what is your cancer risk
HEALTH CHECK
10 Ways to Revitalize Slideshow
SLIDESHOW