Women's Views on Tamoxifen for Breast Cancer Risk Reduction

Walter Price, Dr.P.H., CBCRP Manager–Community Outreach
It has been nearly seven years since the results of the tamoxifen Breast Cancer Prevention Trial were made public. The announced results, a 49 percent reduction in breast cancer incidence among the (high-risk) women taking the drug, compared to those taking the placebo, were striking. Headlines proclaiming that “Tamoxifen Cuts Breast Cancer Risk by 50% in Healthy Women” were common and seemed to herald a new age of breast cancer prevention. Noteworthy also was the reported lower risk of non-invasive breast cancers and fewer bone fractures.

However, when advocacy groups and researchers alike looked behind these headlines (which were reporting the relative risk reduction),a more sobering picture emerged. When looking at the absolute risk reduction, which is the risk of developing breast cancer as a result of taking tamoxifen for each person rather than the (“relative”) risk obtained by comparing women who did take the drug to women who did not take the drug, the effect is much more modest. Among those taking tamoxifen, less than 2 percent got breast cancer, and among those that took the placebo, less than 3 percent got breast cancer. The real (absolute) difference was that 1 percent fewer women in the study population of high risk women taking tamoxifen got breast cancer than did women taking the placebo.

The side effects of tamoxifen use couldn’t be ignored. For women over 50,there was an increased risk of several relatively rare but serious adverse health conditions: blood clots in the lungs, blood clots in major veins, and uterine cancer. At present there is no consensus among advocacy organizations about tamoxifen use for breast cancer risk reduction.

Given this background an important question is how do women now feel about taking tamoxifen for breast cancer prevention? Joy Melnikow, M.D., M.P.H., at the University of California, Davis, and colleagues looked into this question. They used grant funding by the California Breast Cancer Research Program to investigate the attitudes and preferences of higher risk women (ages 39-74) regarding use of tamoxifen for risk reduction. She used a “mixed methods ” study design, gathering and assessing information using qualitative and quantitative methods after providing the (255) higher risk women in the study with a standardized 15-minute educational (English and Spanish) session on the potential benefits and risks of tamoxifen.

Her results, published in May of this year in the journal Cancer, were released to the press in April and received widespread publicity on Fox News and WebMD among other places.

A major finding was that only about 18 percent of women in the study, none of whom had had breast cancer, said that they were inclined to take tamoxifen. An additional 15 percent of the women said that the decision whether or not to take tamoxifen would be very difficult to make. Although they reported that tamoxifen provided a way to satisfy their desire to do something to fight their chances of getting breast cancer, more than half the women cited the risks of side effects as being important in their decision not to take it. Women often felt that they would be trading the risk of developing breast cancer for the risk of developing complications caused by tamoxifen.

Among the findings of the study was the tendency for women to overestimate their numeric five-year risk, often thinking it was ten times higher than it actually was. On average, women thought that they had about one chance in three of getting breast cancer in the next five years; according to criteria used by the Breast Cancer Risk Assessment Program, it was about three in 100.Surprisingly, even in the face to this exaggerated sense of numeric risk, about 70 percent of women said that their risk of breast cancer was “low” or “average.”

Dr. Melnikow and her colleagues concluded that “chemoprevention agents must have few potential adverse effects to achieve widespread acceptance.” It is important, therefore, for researchers in the field to incorporate the goal of minimizing potential adverse long-term effects when considering the next generation of chemoprevention agents to investigate and bring to trial. The CBCRP has funded, and will continue to fund, investigation into naturally-derived compounds that are more likely to have fewer and less serious side effects when used as chemopreventive agents.

(Sources used in this article include news releases by FoxNews, ASCO, Wiley Interscience, NCI website, and Cancer 2005 May; 103 (10).)