Breast Cancer :: Estrogen therapy does not increase breast cancer

While the Women’s Health Initiative Estrogen plus Progestin Trial findings previously reported an increase in breast cancer among those taking combined hormone therapy, the updated analysis reveals that estrogen-alone hormone therapy does not increase the risk of breast cancer in postmenopausal women.

The WHI, sponsored by the National Heart, Lung, and Blood Institute (NHLBI) of the National Institutes of Health, publishes its new analysis in the April 12 issue of the Journal of the American Medical Association.

Over an average of about 7 years of follow-up, study participants taking estrogen had fewer breast cancer tumors than those in the placebo group. Women in the estrogen group were diagnosed with breast cancer at a rate of 28 per 10,000 participants per year versus a rate of 34 per 10,000 participants per year in the placebo group. The difference in rates of breast cancer (6 per 10,000) between the groups was not statistically significant, meaning it could have occurred by chance.

The new analysis also found that participants taking estrogen had 50 percent more abnormal mammograms that required follow-up and underwent 33 percent more breast biopsies.

“Longer follow-up is needed to fully explain the reduced number of breast cancers in women taking estrogen. However, this new analysis does not alter the overall conclusion from the WHI that hormones, including estrogen-alone and estrogen plus progestin, should not be used for the prevention of chronic disease,” said NHLBI Director and WHI Director Elizabeth G. Nabel, M.D.

“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,” she added. Analyses found that women who had a low risk of breast cancer – no family history, no benign breast disease, etc. – had fewer breast cancers on estrogen, while those with higher risk had more breast cancers on estrogen compared to placebo. “This finding underscores the need to individualize treatment for menopause symptoms based on a woman’s medical history and her risk profile,” said WHI Project Officer Jacques Rossouw, M.D.

According to Stanford University’s Marcia Stefanick, Ph.D., the study’s lead author and chair of the WHI Steering Committee, the study improves understanding of the role of estrogen therapy in breast cancer, though more research is needed to explain the subgroup findings.

“What is clear now is that, overall, postmenopausal women without a uterus who choose to take estrogen-alone do not have an increased breast cancer risk, at least over the first 7 years of treatment. This is clinically relevant, but women who are taking estrogen should also be aware that they will likely need more repeat mammograms and more breast biopsies,” she said.

Rossouw, however, said more research is needed on the role of progestin. According to Rossouw, the increased risk of breast cancer found in women taking combined hormones may be due to the effects of progestin – when it is combined with estrogen.


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