One kind of hormone replacement therapy may help reduce the risk of breast cancer several years after women stop treatment, researchers reported today.
The findings, from the large US Women’s Health Initiative (WHI) trial, are based on 10,739 postmenopausal women who had undergone hysterectomy.
Previous results from the trial indicated that women taking oestrogen hormone replacement therapy (HRT) had a lower rate of breast cancer than did those on placebo.
Other studies of HRT have discouraged long-term use because of other side-effects.
So to look at the longer-term effects, the women were followed for about five years after stopping HRT. Use of oestrogen HRT for about six years was linked with a 23 per cent lower risk of breast cancer. This benefit seemed to be limited to women at low risk of breast cancer, based on their medical history and family history.
Dr Garnet Anderson of the Fred Hutchinson Cancer Research Centre, Seattle, USA, and colleagues report their findings in the Lancet Oncology today.
Dr Anderson said: "These latest results should provide reassurance about breast safety of oestrogen use for durations of about five years for women with a hysterectomy seeking relief from postmenopausal symptoms.
"However, 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 and the additional risk of stroke and blood clots."
Commenting on the study, Dr Anthony Howell of the University Hospital of South Manchester, UK, says the results "should be seen in the context of the update of the study in 2011 reporting the effects of oestrogen on overall health – no overall difference was noted in participants’ global index of health (including cardiovascular disease, thrombosis and embolism, breast and colorectal cancer, hip fracture, and death from all causes)."
Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women’s Health Initiative randomised placebo-controlled trial. Anderson, G. L. et al. The Lancet Oncology March 7 2012 doi:10.1016/S1470-2045(12)70075-X
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