WHI: Estrogen-Only HRT Continues to Protect Women Against Breast Cancer

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(ChemotherapyAdvisor) – A follow-up study of 7,645 women from the Women's Health Initiative (WHI) trial who took estrogen for approximately six years and then stopped were less likely to develop breast cancer and remained significantly less likely to die than those who never used hormone replacement therapy, a study published in The Lancet Oncology online first March 7 has found.

The study sample represented 78% of the original surviving WHI members who were tracked from March 2005 until August 2009, a median of 4.7 years after stopping estrogen therapy.

Use of estrogen was associated with a 23% reduction in incidence of invasive breast cancer (151 cases, 0.27% per year) vs. placebo (199 cases, 0.35% per year; P=0.02). Women in the estrogen group who did develop breast cancer had a 63% reduction in death from the disease (6 deaths, 0.009% per year) vs. placebo (16 deaths, 0.024% per year), as well as from any cause after a diagnosis of breast cancer, 30 vs. 50 deaths (HR 0.62; P=0.04).

Breast-cancer risk reduction with estrogen use was found to be concentrated in women without benign breast disease or a family history of breast cancer, according to subgroup analyses.

“Our findings provide reassurance for women with hysterectomy seeking relief of climacteric symptoms in terms of the effects of estrogen use for about five years on breast cancer incidence and mortality,” the investigators concluded. “However, our data do not support use of estrogen for breast-cancer risk reduction because any noted benefit probably does not apply to populations at increased risk of such cancer.”

Abstract

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