Tamoxifen as Prevention Questioned
Popular Breast Cancer Drug May Not Lengthen Life for Most
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
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
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
"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
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
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