The Women's Health Resource. On the web since 1997.

Study: 2 Million Healthy Women Would Benefit from Breast Cancer Prevention Drug (dateline July 31, 2003)


A recent study finds that approximately 10 million healthy women would be eligible to take the drug tamoxifen to reduce their chances of developing breast cancer. Of those women, over two million are likely to reap the benefits of the drug without experiencing side effects. Tamoxifen has been approved by the U.S. Food and Drug Administration (FDA) since 1998 to help prevent breast cancer in women determined to be at high risk for the disease. However, the risk of potentially severe side effects has deterred some physicians from prescribing it and some women from taking it. This new study shows that tamoxifen has the potential to significantly prevent breast cancer in the United States.

The study, conducted by Andrew N. Freedman, Ph.D. and colleagues from the National Cancer Institute estimated the total number of U.S. women, aged 35–79 years, who would be eligible to take tamoxifen based on the FDA eligibility criteria.

Summary of study results:

  • An estimated 15.5% of American women between the ages of 35 to 79 (approximately 10 million women) would be eligible to take tamoxifen based exclusively on breast cancer risk.
  • Based on an analysis by race, 18.7% of white women ages 35 to 79 (approximately 9.4 million) would be eligible to take tamoxifen, and 4.9% (approximately 2.4 million) of these women would likely benefit from tamoxifen; and,
  • 6% of African-American women aged 25 to 79 (approximately 430,000) would be eligible to take tamoxifen, and 0.6% (approximately 43,000) of these women would likely benefit from tamoxifen.*
  • Younger women are more likely than older women to benefit from tamoxifen because they are less likely to experience side effects from the drug.

*The lower estimated number of African-American that would benefit from tamoxifen was derived from the fact that breast cancer is less common in African-Americans, compared to white women. In addition, the rates of some of the serious side effects of tamoxifen, including stroke, deep vein thrombosis, and pulmonary embolism, are higher in African-Americans compared to white women.

Using their estimate that 2.4 million of white women would benefit from taking tamoxifen, Dr. Freedman and his colleagues concluded that if all of these women took tamoxifen, 28,492 breast cancer cases could be prevented or deferred within the next five years.

A large study by the National Adjuvant Breast and Bowel Project, entitled the Breast Cancer Prevention Trial, previously found that tamoxifen could reduce the chances of developing breast cancer in high risk women by as much as 49%. However, this benefit should be weighed against the relatively rare but serious side effects of the drug, including:

  • endometrial cancer (cancer of the lining of the uterus)
  • deep vein thrombosis (blood clots in large veins, particularly in the legs)
  • pulmonary embolism (blood clot in the lung)
  • stroke

"Our study makes progress in evaluating the potential public health impact of tamoxifen use and identifies subgroups of women who may especially benefit from tamoxifen," said Dr. Freedman, in a National Cancer Institute news release. "Although these findings suggest a benefit of tamoxifen for certain women, the choice to take tamoxifen is an individual one. Women with increased risk of breast cancer must carefully consider the benefits and risks in consultation with their physicians."

Additional Resources and References