The Pharmaceutical Journal
Vol 276 No 7397 p470
22 April 2006

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Oestrogen-only HRT does not raise breast cancer risk

Postmenopausal women who take oestrogen-only hormone replacement therapy do not have an increased risk of breast cancer, according to an analysis of data from the Women's Health Initiative published last week (JAMA 2006;295:1647). These results are in contrast to the WHI trial of a combined oestrogen and progestogen product, which showed an increase in breast cancer incidence (PJ, 13 July 2002, p43).

Researchers looked at data from 10,739 postmenopausal women with a prior hysterectomy who were randomised to receive conjugated equine oestrogen or placebo and were followed up for a mean of 7.1 years. Incidence of invasive breast cancer did not differ significantly between the two groups (hazard ratio 0.80, 95 per cent confidence interval 0.62–1.04; P=0.09). Subgroup analysis, which the researchers say should be interpreted with caution, suggests reductions in ductal carcinomas, and in invasive breast cancers in women who were adherent to study medication.

From the first year onwards, an increase in the frequency of mammograms requiring follow-up was seen in the HRT group compared with the placebo group (9.2 per cent versus 5.5 per cent; P<0.001). This increase was maintained throughout the trial but was concentrated in the category of recommended short-term follow-up (ie, repeat mammography after six months).