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Prior use of oestrogen only HRT reduces breast cancer risk

HRT use five years previously linked to 20% lower risk of breast cancer

Ingrid Torjesen

Wednesday, 07 March 2012

Women who use the oestrogen-only form of hormone replacement therapy (HRT) appear less likely to develop breast cancer in the longer term, according to new research published online in The Lancet Oncology.

The follow-up study, which involved over 7500 women from the Women’s Health Initiative (WHI) trial who took oestrogen for about 6 years and then stopped, found that these women were more than 20% less likely to develop breast cancer and remain significantly less likely to die from the disease than those who never used HRT nearly 5 years after stopping treatment.

Lead researcher Garnet Anderson from the Fred Hutchinson Cancer Research Center, Seattle, USA, said: “These latest results should provide reassurance about breast safety of oestrogen use for durations of about 5 years for women with a hysterectomy seeking relief from postmenopausal symptoms.”

The WHI trial was begun to investigate the effects of conjugated equine oestrogen versus placebo on chronic disease in women who had previously had a hysterectomy. The trial was stopped in 2004 (a year earlier than planned) because of an increased risk of stroke and blood clots. This new analysis reports  the overall effects of oestrogen use on breast cancer incidence and mortality, in extended follow up of 78% of the original surviving participants.

The researchers found a 23% reduction in the incidence of invasive breast cancer compared with placebo during an overall follow-up period of nearly 12 years, whilst women in the oestrogen group who did develop breast cancer had a 63% reduction in deaths from the disease compared with those in the placebo group.

The lower risk of breast cancer was restricted to women without a history of benign breast disease or a strong family history of breast cancer.

Mr Anderson said: “The continued postintervention effect of oestrogen on breast cancer incidence is akin to that reported for other hormone-targeted drugs shown to reduce breast cancer incidence.”

However, he added: “Our data do not support the use of oestrogen for breast cancer risk reduction in light of the lack of benefit noted in populations at higher risk (including those with a strong family history of breast cancer or benign breast disease) and the additional risk of stroke and blood clots.”

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