Estrogen-only form of menopausal hormone therapy may protect against breast cancer

Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center (LA BioMed)Mar 12 2012

Rowan T. Chlebowski, M.D., Ph.D., an LA BioMed investigator whose research activities have focused on breast cancer therapy and prevention, and chronic diseases impacting women's health, is co-author of a study that indicates that women who use the estrogen-only form of menopausal hormone therapy appear less likely to develop breast cancer in the longer term, according to new research which was recently published The Lancet Oncology.

A follow-up study of over 7,500 women from the Women's Health Initiative (WHI) trial who took estrogen for about 6 years and then stopped has found that they are over 20 percent less likely to develop breast cancer and remain significantly less likely to die from the disease than those who never used HRT, a period of nearly 5 years after stopping treatment.

"These findings are important in that they provide substantial reassurance regarding the safety of estrogen alone use for women with climacteric symptoms initiated close to menopause for duration similar to those used in this study," said Dr. Chlebowski. "Previously, concern regarding estrogen influence on breast cancer may have inhibited women from considering such therapy."

In 1993, the WHI trial of estrogen alone was established to investigate the effects of conjugated equine estrogen on chronic disease. Nearly 11,000 postmenopausal women ages 50 to 79 who had previously had a hysterectomy were given estrogen or placebo over a period of nearly 7 years. The trial was stopped in 2004 (a year earlier than planned) because of an increased risk of stroke and blood clots.

In this new study, Dr. Chlebowski and his colleagues report the overall effects of estrogen use on breast cancer incidence and mortality, including extended follow-up of 7,645 women (78 percent of the original surviving members) who were tracked from March 2005 until August 2009, a median (midpoint) 4.7 years after stopping estrogen therapy.

The researchers found a 23 percent reduction in the incidence of invasive breast cancer compared with placebo (151 cases, 0.27% per year vs. 199 cases, 0.35% per year) during an overall follow-up period of nearly 12 years, while women in the estrogen group who did develop breast cancer had a 63 percent reduction in deaths from the disease (six deaths, 0.009% per year vs. 16 deaths, 0.024% per year) compared with those in the placebo group.

The lower risk of breast cancer was restricted to women without a history of benign breast disease or a strong family history of breast cancer. They say: "The continued postintervention effect of estrogen on breast cancer incidence is akin to that reported for other hormone-targeted drugs shown to reduce breast cancer incidence."

However, the researchers also caution: "Our data do not support the use of estrogen for breast cancer risk reduction in light of the lack of benefit noted in populations at higher risk (including those with a strong family history of breast cancer or benign breast disease) and the additional risk of stroke and blood clots."