Does HRT Cause Breast Cancer or Not?

Breast cancer study conclusions linking HRT and breast cancer questioned

/ Author:  / Reviewed by: Joseph V. Madia, MD

(RxWiki News) Women used to rely on hormonal replacement therapy (HRT)​ to calm the discomforts of menopause. Then a study linked HRT to breast cancer, and everything changed.

A recent review questioned the conclusions of studies linking HRT and breast cancer. The researchers cited study flaws, biology and time as part of their reasoning.

According to the reviewers, there’s not enough evidence to support or reject the claim that HRT causes breast cancer.

A noted breast cancer expert disagrees.

"Talk to a gynecologist about hormone therapy."

Researchers from around the world pored through five studies that connected HRT to increased breast cancer risks.

“Causal principles” (statistical ways of establishing cause and effect) were applied to the studies. Samuel Shapiro, PhD, of the University of Cape Town Medical School in Cape Town, South Africa, led the review.

The Collaborative Reanalysis, the Women's Health Initiative and the Million Women Study were the original studies that suggested the HRT-breast cancer link. These studies are credited with causing the dramatic decrease of HRT use starting in 2002. 

Follow-up studies published in 2006 and 2007 concluded that declining HRT use mirrored declines in the number of breast cancers being diagnosed.

The recent review highlighted problems with these studies and their conclusions:

  • Breast cancer rates actually started declining in 1999, three years before the studies linking HRT and breast cancer came out in 2002.
  • It takes years for breast cancer tumors to develop. As a result, declining rates would have been expected to be seen over a longer period of time.
  • A study that found an 11 percent drop in 2003 is “not credible,” according to the researchers, because one year isn’t long enough to make such a dramatic difference.
  • One study, which relied on US National Cancer Institute's Surveillance, Epidemiology and End Results (SEER) data, saw drops in both early and advanced breast cancers. The researchers said it was “very unlikely” that advanced disease, which takes longer to develop, would have declined as quickly as early cancers.

"Based on the observed trends in the incidence of breast cancer following the decline in HRT use, the ecological evidence is too limited either to support or refute the possibility that HRT causes cancer," the authors concluded.

Breast cancer specialist Adam Brufsky, MD, PhD, told dailyRx News, “I disagree. Estrogens clearly stimulate breast cancer growth, and the decline in HRT use correlates in time to a decline in the incidence of breast cancer."

“The authors of this analysis do not have any other acceptable alternative hypothesis for this correlation. Until we have a better explanation, most oncologists will continue to believe the hypothesis, and this study will do little if anything to change that view,” said Dr. Brufsky, professor of medicine at the University of Pittsburgh School of Medicine.

Published March 14 in the Journal of Family Planning and Reproductive Health Care, this is the last of a five critiques on HRT studies.

No outside funding supported this research. All of the authors presently consult, and in the past have consulted, with manufacturers of products discussed in this article.

Reviewed by: 
Review Date: 
March 14, 2013
Last Updated:
September 26, 2013