Estrogen Therapy In Young Women May Not Increase Breast Cancer Risk

Dr. Clarice R. Weinberg Ph.D Biostatistics and Computational Biology Branch National Institute of Environmental Health Sciences Research Triangle Park, NC Interview with:
Dr. Clarice R. Weinberg Ph.D
Biostatistics and Computational Biology Branch
National Institute of Environmental Health Sciences
Research Triangle Park, NC 27709

MedicalResearch: What is the background for this study?

Dr. Weinberg: Hormone therapy (HT) was commonly prescribed in the U.S. late in the 20th century to help women through the challenges of menopause. Several decades ago, therapy with estrogen alone was shown to cause endometrial cancer, and the combined use of both estrogen and progesterone replaced treatment with estrogen alone. But research published around 2002 had far reaching effects on gynecologic practice. Both the randomized trial component of the US Women’s Health Initiative and the observational European Million Women’s Study reported that postmenopausal women who were older than 50 and were taking the combination HT had an increased risk of breast cancer. Physicians and patients responded quickly, and Hormone therapy use plummeted.

However, it remained unclear whether there were risks of Hormone therapy use in women under age 50. Some factors, for example obesity, have opposite effects on the risk of breast cancer in pre- and post-menopausal women, so one cannot assume risk findings from older women necessarily apply to younger women. We carried out a sibling-based study of 1,419 women with breast cancer diagnosed under the age of 50 ( Each case had a sister (also studied) who had never been diagnosed with breast cancer, who could serve as her control. The study was funded by Susan G. Komen for the Cure, and the National Institutes of Health.

MedicalResearch: What are the main findings?

Dr. Weinberg: We estimated that women who had only taken estrogen (without progesterone) had a 42 percent decrease in their risk of young-onset breast cancer, compared to women of similar age who had never taken Hormone therapy. Women who had taken the combination estrogen plus progesterone showed no increase in risk, but there were few with this exposure and we cannot rule out increased risk for the combination therapy. Interestingly, participants in the Women’s Health Initiative who were randomized to estrogen alone had reduced risk of fractures and reduced risk of breast cancer. However, that study had to be discontinued because those women showed increased risk of stroke.

MedicalResearch: What should clinicians and patients take away from your report?

Dr. Weinberg: In women under age 50, estrogen therapy does not appear to increase the risk of breast cancer. We did not study whether use of estrogen before 50 might affect risk at later ages.

MedicalResearch: What recommendations do you have for future research as a result of this study?

Dr. Weinberg: Our data suggest that estrogen use before age 50 is less harmful than commonly assumed, and might actually confer some protection against breast cancer. However, these findings require replication through additional research. Since a randomized trial would probably not be feasible, we would like to see an observational study that carefully ascertains the indications for use when a young woman reports taking estrogen alone. Such data will be helpful in ruling out the possibility that it is the underlying indications and not the estrogen that confers protection against breast cancer. Prospective follow up beyond age 50 would also be valuable.


Hormone Therapy and Young-Onset Breast Cancer

Katie M. O’Brien, Chunyuan Fei, Dale P. Sandler, Hazel B. Nichols, Lisa A. DeRoo, and Clarice R. Weinberg
Am. J. Epidemiol. first published online February 18, 2015 doi:10.1093/aje/kwu347 Interview with: Dr. Clarice R. Weinberg Ph.D (2015). Estrogen Therapy In Young Women May Not Increase Breast Cancer Risk 

Last Updated on March 8, 2015 by Marie Benz MD FAAD