Use of Tamoxifen To Prevent Breast Cancer Would Benefit 2.4 Million Women, Study Finds

Taking the breast cancer treatment tamoxifen to prevent breast cancer would benefit an estimated 2.47 million women, mostly middle-aged and white, despite the drug's risks, a new study has found, the AP/Boston Globe reports. For the study, published in the current Journal of the National Cancer Institute, researchers estimated that 10 million women ages 35 to 79 are eligible for preventive tamoxifen because they are at increased risk of developing breast cancer within five years. After subtracting the women most at risk of serious side effects -- which include endometrial cancer, blood clots in the legs and lungs, stroke and cataracts -- they determined that 2.47 million women could potentially benefit from tamoxifen without excessive harm (Neergaard, AP/Boston Globe, 4/2). The researchers based their estimates on the 2000 National Health Interview Survey Cancer Control Module (Freedman et al., "Estimates of the Number of U.S. Women Who Could Benefit From Tamoxifen for Breast Cancer Chemoprevention" abstract, Journal of the National Cancer Institute, 4/2). The FDA in 1998 approved the use of tamoxifen to prevent breast cancer for women ages 35 and older with a 1.67% risk of developing the disease over five years. Fewer than 60,000 women currently take tamoxifen preventively, according to AstraZeneca, which produces a version of the drug (Rubin, USA Today, 4/2). If 2.47 million women took tamoxifen for five years, 28,000 breast tumors could be avoided or delayed, according to the study.

The study found that the best candidates for the drug are white women ages 40 to 59 who have a high risk of developing breast cancer. Women in their 50s who have had hysterectomies were found to be optimal for using the drug, because they would not be able to contract uterine cancer, one of tamoxifen's risks (AP/Boston Globe, 4/2). The study concluded that the benefits of preventive tamoxifen outweighed the risks for 4.9% of white women and 0.6% of black women (USA Today, 4/2). Researchers estimated that only 43,000 black women would benefit from taking tamoxifen because breast cancer is less common among black women and because blacks have higher rates of blood clots (AP/Boston Globe, 4/2). Accurate data on the risks of tamoxifen in Hispanic women was not available (USA Today, 4/2).

American Society of Clinical Oncology spokesperson William Gradishar said the study "brings home the message that we have chemoprevention strategies that ... aren't being as widely implemented" as their potential benefits suggest they should be (AP/Boston Globe, 4/2). However, Barbara Brenner, executive director of the advocacy group Breast Cancer Action, said, "The authors fail to consider the long-term effects of tamoxifen on the health of women given tamoxifen for a five-year period (the recommended duration for cutting risk) at relatively young ages," adding, "They can't consider those effects, because they've never been studied." Study co-author Worta McCaskill-Stevens of the National Cancer Institute said "Tamoxifen is a choice. It's not for every woman" (USA Today, 4/2). An abstract of the study is available online.