New Analysis of Estrogen Therapy and Breast Cancer
Risk
 Estrogen-alone
hormone therapy does not increase the risk of breast cancer in postmenopausal
women, according to a new analysis of results from the Women's Health Initiative
(WHI), one of the largest medical studies ever.
The Estrogen-Alone portion of the WHI involved 10,739 generally healthy postmenopausal
women ages 50-79 who did not have a uterus. Estrogen-alone therapy (without progestin)
is only recommended for women without a uterus; those with a uterus who take
estrogen have an increased risk of endometrial cancer, so they are advised to
take estrogen combined with progestin.
The study was stopped at the end of February 2004 because of an increased risk
of stroke and no significant effect on heart disease. Other findings from the
study at the time were that estrogen increased the risk of blood clots in the
legs, reduced the risk of hip fractures and had no significant effect on colorectal
cancer.
The effect of estrogen on breast cancer was uncertain. This new report, published
in the April 12 issue of the Journal of the American Medical Association,
provides a more detailed analysis of 237 invasive breast cancers.
Over an average of about 7 years of follow-up, the women taking estrogen had
fewer breast cancer tumors than those in the placebo group, but the difference
between the two groups was not statistically significant — in other words,
it could have happened by chance. These results contrast with results from the
WHI's Estrogen plus Progestin Trial, which found an increase in breast cancer
over about 5 years among those taking the combined hormone therapy. The new analysis
did find, however, that participants taking estrogen had 50% more abnormal mammograms
that required follow-up and underwent 33% more breast biopsies.
Dr. Elizabeth G. Nabel, Director of NIH's National Heart, Lung, and Blood Institute,
which sponsored the study, commented, "The findings still support current recommendations
that hormone therapy should only be used to treat menopausal symptoms and should
be used at the smallest effective dose for the shortest possible time."
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