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Menopause Health Center

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Estrogen Alone Has Little Benefit, Some Harm

No Effect on Breast Cancer, Heart Disease, but Increases Stroke Risk
WebMD Health News

March 2, 2004 -- In long-awaited results, researchers have found that giving estrogen alone to postmenopausal women has no good or bad effect on breast cancer or heart disease but does raise the risk of having a stroke.

The National Institutes of Health (NIH) halted the first arm of the study -- Prempro, estrogen plus progestin -- in July 2002 because of an increased risk of breast cancer in women taking the combination menopausal hormone therapy. But it allowed a second arm of the study to continue. That arm -- in which women who had hysterectomies received estrogen only (Premarin) -- has now been stopped one year ahead of schedule.

The main goal of the study was to see whether starting menopausal hormone therapy might lower a woman's risk of heart disease. It did not. In the estrogen-only group, there was no increase or decrease in heart disease.

However, women taking estrogen-only hormone therapy had a slightly increased risk of stroke. That risk translates into about eight extra strokes for every 10,000 women taking Premarin. Estrogen-only hormone therapy reduced women's risk of hip fracture. But in the opinion of the NIH, that benefit did not outweigh the additional risk because there are other effective ways to fight bone loss.

Women taking estrogen also tended to develop more dementia or mild thinking problems than women taking placebo pills, though this could have been a chance finding.

Estrogen-only hormone therapy did not affect a woman's risk of breast cancer.

The Right Thing

The NIH says it stopped the trial because the next and final year of study was unlikely to yield any new information. Even though participants had already been warned about the slightly increased risk of stroke with continued estrogen treatment, the NIH saw no point in exposing them to further risk.

The decision was made after a meeting by leaders of all relevant institutes in the National Institutes of Health, says Barbara Alving, MD, director of the WHI trial and acting director of the National Heart, Lung, and Blood Institute.

"We learned all we need to learn. Another year will not change our conclusions," Alving said in a news conference.

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