Study Finds Estrogen Replacement Lowers Risk of Breast Cancer For Some Women

March 6, 2012— -- Millions of women seeking relief from hot flashes, night sweats and other postmenopausal symptoms -- but fearing the risks of hormone replacement therapy -- have some reassurance from new research on estrogen-only HRT.

A new study suggests that estrogen-only HRT may lower the risk of breast cancer for some postmenopausal women. However, the findings apply to a particular subset of those women -- those who have had a hysterectomy, have no increased risk of breast cancer and no increased risk of strokes and blood clots.

The research came as a follow-up to the Women's Health Initiative, a 10-year study of more than 10,000 women taking HRT. The trial was halted in 2004 amid concerns that the treatments increased women's risk of stroke and breast cancer. The end of the trial was followed by a drop in the number of women taking estrogen for their postmenopausal symptoms. A study from the North American Menopause Society found that the use of estrogen dropped by 71 percent from 2001 to 2009.

The concerns that stopped the trial were mostly linked to combined HRT -- a combination of estrogen and progestin, which doctors still say increases a woman's risk of breast cancer. Garnet Anderson, the lead author of the study, said fear over those risks tainted the reputation of estrogen-only HRT, even though researchers had already observed that it seemed to reduce the risk of breast cancer.

"These new data suggest that women don't have to be afraid of taking estrogen-only HRT," she said.

Researchers studied more than 7,500 postmenopausal women who had undergone a hysterectomy and had taken estrogen-only HRT as a part of the Women's Health Initiative. The women, aged 50 to 79, took estrogen for six years and then stopped when the trial was halted.

But researchers continued to monitor the women for the next five years and found that the women who took estrogen were 23 percent less likely to develop breast cancer than those who took a placebo. Of the women taking estrogen-only HRT who did develop breast cancer, the study found that they were less likely to die from the disease. Six women taking estrogen died of the disease, compared with 16 in the group taking a placebo.

Dr. Jacques Rossouw, chief of the Women's Health Initiative at the National Heart, Lung and Blood Institute, said the study suggests that the length of time a woman takes estrogen may play a role in her risk of developing breast cancer.

"If they use it [estrogen] for short term and then stop after 6 years or so, they are not at increased risk of breast cancer," he said. He cautioned, however, that the use of estrogen for longer periods may increase the risk.

Women who have not had a hysterectomy should not take estrogen-only HRT, since estrogen increases the risk of uterine cancer.

The findings, published today in the medical journal The Lancet, give a little more clarity for women who want relief from their postmenopausal symptoms but feel confused by all the conflicting information on whether or not HRT is safe. Dr. Janet Pregler, director of the Iris Cantor-UCLA Women's Health Center, said her patients are often frustrated by the conflicting reports on HRT. But she said she has prescribed estrogen alone for several years to her postmenopausal patients who have had hysterectomies.

"There's no question that hormones remain the best treatment for hot flashes and night sweats," Pregler said. "The risk of doing that for a few years around menopause is really very low, depending on other health risks you have."

The study found several caveats to the effectiveness of estrogen-only HRT. The reduced risk of breast cancer applied only to women who were not already at risk for the disease. As a result, Anderson said patients should not take estrogen with the goal of reducing breast cancer risk.

Also, HRT is still associated with an increased risk of stroke, and doctors say that women who are at increased risk of stroke and blood clots should still avoid taking any HRT.