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Tamoxifen as Prevention Questioned

Popular Breast Cancer Drug May Not Lengthen Life for Most
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.

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