Why don’t more women use Tamoxifen to prevent breast cancer?

In CA, a cancer journal for doctors, a recent article documents that women are not taking a drug known to prevent breast cancer. In "Tamoxifen Infrequently Used by Women at Risk for Breast Cancer", John Henry Dreyfuss reports that:

The prevalence of Tamoxifen use for the primary prevention of breast cancer is "exceptionally low" among women in the United States, according to an analysis of National Health Interview Survey (NHIS) data published recently in Cancer Epidemiology, Biomarkers & Prevention (2010;19:443-446).

According to results of the Breast Cancer Prevention Trial published in 1998, Tamoxifen reduced the risk of developing invasive breast cancer by 49%, and the relative risk reduction for estrogen receptor-positive invasive breast cancer was 69% (J Natl Cancer Inst. 1998;90:1371-1988). Despite this substantial risk reduction, subsequent studies have indicated that Tamoxifen is used for chemoprevention by only a very small percentage of eligible women.

According to studies of Tamoxifen:

A 2003 analysis of data obtained from the 2000 NHIS suggested that 15.5% of white women and 5.7% of black women ages 35 to 79 years were eligible for Tamoxifen chemoprevention based on the eligibility criteria of the US Food and Drug Administration and that the benefits outweighed the risks for 4.9% of white women and 0.6% of black women (J Natl Cancer Inst. 2003;95:526-532.).

Nonetheless, in their current study of NHIS data, lead author Erika A. Waters, PhD, et al reported that "In 2000, 0.2% of US women ages 40 to 79 [years] without a personal history of breast cancer took Tamoxifen for chemoprevention (95% confidence interval [95% CI], 0.13-0.31). In 2005, the prevalence was 0.08% (95% CI, 0.03-0.17)."

Tamoxifen is only for "high risk" women but even then the Waters study shows that it is underutilized by physicians as reported in CA:

"We are not suggesting that Tamoxifen is appropriate for everyone," Dr. Waters tells CA. "The decision to take Tamoxifen, and Tamoxifen now, is a very important decision that should be made on an individual basis between a woman and her doctor. It’s a difficult decision and there are a lot of factors to consider beyond…the probability of developing breast cancer." Dr. Waters is an assistant professor at the Washington University School of Medicine in St. Louis, Missouri.

Since a woman taking a chemoprevention drug does not if she is free of breast cancer because of the drug or because of other factors. All the women know is that they don’t have breast cancer. The side effects include hot flashes and blood clots so there are risks also associated with taking this drug. The article in CA suggests that doctors need better ways of communicating the risks and benefits of chemoprevention to women at risk of breast cancer. Any woman who has been diagnosed with breast cancer certainly would have preferred to avail herself of a drug that prevents the disease. Hopefully doctors will take these studies to heart and better educate their patients about chemoprevention.

The article can be found at:

CA Cancer J Clin 2010; 60:204-206
doi: 10.3322/caac.20080
© 2010 American Cancer Society