Estrogen-Only Hormone Replacement Therapy May Reduce Breast Cancer Risk

While some forms of hormone replacement therapy have been found to increase breast cancer risk, therapies that use only estrogen may actually protect women against the disease, a new study says.

Women in the study who took estrogen-only hormone replacement therapy (HRT) for six years were 23 percent less likely to develop breast cancer five years after they had stopped the therapy compared with women who never received HRT. Women who took estrogen-only HRT were also less likely to die of breast cancer.

The findings mostly apply to women who have had a hysterectomy, as this is the group most likely to take estrogen-only HRT. The therapy raises the risk of uterine cancer, so the therapy is usually not prescribed for other women.

"These latest results should provide reassurance about breast safety," for women taking estrogen for about five years after a hysterectomy for relief from postmenopausal symptoms, said study researcher Garnet Anderson, of the Fred Hutchinson Cancer Research Center in Seattle.

However, the researchers said they do not recommend estrogen-only HRT as a way to reduce breast cancer risk in general. The lowered risk was not found in women with a family history of the disease, and the therapy comes with a risk of stroke and blood clots, the researchers said.

The study will be published online March 7 in the journal Lancet Oncology.

Does HRT cause harm?

In the 1990s, the Womens Health Initiative, a study involving more than 100,000 women, was established to determine the risks and benefits of HRT. One branch of the study looked the effects of taking estrogen and progestin together, but it was halted ahead of schedule in 2002 because the hormone combination was found to increase the risk of breast cancer by 25 percent.

A separate study branch looked at the effect of estrogen-only HRT in 11,000 postmenopausal women who had had hysterectomies. This trial was stopped in 2004 because the therapy was found to increase the risk of stroke and blood clots.

In the new study, the researchers followed 7,645 women from the estrogen-only branch for about five years after the trial ended. About half had taken estrogen during the trial, and half had taken the placebo.

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Estrogen-Only Hormone Replacement Therapy May Reduce Breast Cancer Risk