For years, doctors have warned that hormone replacement therapy, or HRT, is linked with an increased risk of breast cancer. Now, new Canadian research suggests that estrogen-only HRT may actually lower the risk of breast cancer in some women.
The study finds that among menopausal women who have had a hysterectomy and who have no family history of breast cancer, taking estrogen replacement therapy can lower their risk of breast cancer by 30 to 40 per cent.
The study was presented this week at the annual San Antonio Breast Cancer Symposium and has not been peer-reviewed.
The study's lead author, Dr. Joseph Ragaz, a medical oncologist and clinical professor at the School of Population and Public Health at The University of British Columbia, acknowledges the results appears to contradict the widely held belief about HRT.
"Our analysis suggests that, contrary to previous thinking, there is substantial value in bringing HRT with estrogen alone to [treatment] guidelines," said Ragaz in a press release.
"The data show that for selected women it is not only safe, but potentially beneficial for breast cancer, as well as for many other aspects of women's health."
Ragaz and his colleagues re-analyzed data from HRT trials of the Women's Health Initiative (WHI). It was that trial in 2002 that showed that the combination of estrogen and progesterone appeared to increase the risk of breast cancer.
At the time, the effects of estrogen alone on breast cancer risk were reviewed, but the results were not conclusive. Ragaz and his team reanalyzed the WHI studies and found that subsets of women with no family history of breast cancer who received estrogen alone after a hysterectomy had a significantly reduced breast cancer incidence.
In addition, the 75 per cent of women without benign disease prior to the trial enrolment also had a reduced breast cancer risk.
As well, women who took estrogen alone also had 40 per cent fewer heart attacks, and there was a 40 to 50 per cent reduction of advancing osteoporosis, the analysis found.
Ragaz concedes that further research is needed. That research will need to focus on understanding the mechanisms that would allow HRT estrogen to prevent breast cancer, as well as to define which patients would be best suited for the therapy.
Dr. Timothy Rowe, the Head of the Division of Reproductive Endocrinology and Infertility at the University of British Columbia, and the editor of the Journal of Obstetrics and Gynecology Canada, says the results are exciting, but need a lot more study.
"We have had a hunch for some time that estrogen or this particular estrogen used in the women's health initiative was protective against breast cancer but this was the first evidence from that data set that it is in fact protective," he told CTV News.
"I don't think any single study really should have the last word in anything as significant as this. I mean, breast cancer is a huge public health issue; it is a huge personal health issue. And if we are saying something as bold as, ‘Listen, this form of estrogen is going to reduce your risk,' then we have to be very sure that we are right."
