MedicalResearch:What is the background for this study?
Dr. Nichols: Tamoxifen, a drug that is often used to treat breast cancer, has also been approved to prevent breast cancer in women who may be at high risk for developing the disease. Taking tamoxifen for 5 years can lower breast cancer risk by up to 48%. The United States Federal Drug Administration (FDA) approved tamoxifen for breast cancer prevention more than 15 years ago (in 1998) for women ages 35 and older who are at high risk of breast cancer and who are at low risk for serious side effects.
National estimates show that <1% of women who are eligible to use tamoxifen actually use it for breast cancer prevention. While tamoxifen lowers breast cancer risk it does cause hot flashes and may lead to serious side effects such as cataract, stroke, and uterine cancer. Women who start taking tamoxifen may also stop taking it before the recommended 5-years due to side effects.
We used a tool developed by scientists at the National Cancer Institute (NCI) to calculate whether the benefits of tamoxifen outweighed the risks for women in the Sister Study, a study of more than 50,000 U.S. and Puerto Rican women with a family history of breast cancer. The tool uses information on a woman’s age, race, breast cancer risk, menopausal status, and whether she had a hysterectomy (surgical removal of the uterus) to estimate whether there is no, moderate or strong evidence that the benefits of tamoxifen will outweigh the risks.
MedicalResearch: What are the main findings?
Dr. Nichols: In the Sister Study of 50,884 women ages 35-74, 788 women (1.5%) told us they took tamoxifen to prevent breast cancer. Overall, 74% of tamoxifen users had moderate to strong evidence that the benefits outweighed the risk. For 20% of tamoxifen users, the benefits did not appear to outweigh the benefits. Women who were younger (35-49 versus ≥50), non-Hispanic White (compared to African American), or had a hysterectomy (compared to those with an intact uterus) appeared more likely to have a net benefit of tamoxifen use.
We also found that African-American and Hispanic women were half as likely as non-Hispanic White women to report using tamoxifen. Tamoxifen use was more common among women who had had a hysterectomy but had not used estrogen therapy, and among women who had stronger family histories of breast cancer. We also saw that women who had the highest estimated breast cancer risk and had strong evidence that the benefits of tamoxifen would outweigh the risks were more likely to use tamoxifen.
Almost half (46%) of all tamoxifen users stopped taking it before the recommended 5 years. Few factors in our study, including age, race, menopausal status or estimated breast cancer risk were related to stopping tamoxifen early (before 5 years).
MedicalResearch: What should clinicians and patients take away from your report?
Dr. Nichols: Breast cancer prevention with drugs like tamoxifen may be appropriate for women at high risk of breast cancer due to a strong family history. Tools such as the Risk-Benefit Index developed at NCI can help patients and providers weigh the risks and benefits of these drugs. It may be especially important for women over 50, African American women, and women who have not had a hysterectomy to discuss with their doctor whether the benefits of tamoxifen are likely to outweigh the risks.
MedicalResearch: What recommendations do you have for future research as a result of this study?
Dr. Nichols: The Sister Study, led by investigators at the National Institute of Environmental Health Sciences, provided an important opportunity to examine tamoxifen use for breast cancer prevention among women with a family history of breast cancer. However, many questions remain unanswered. Future research avenues critical to this issue will include understanding how patients and healthcare providers talk about breast cancer prevention, and identifying ways to reduce side effects and other barriers to initiating or completing the full 5 years of therapy.