A new report based on data from the Women's Health Initiative (WHI ) study has found that combined hormone replacement therapy (HRT), containing oestrogen and progestin, is associated with a very small increased risk of mortality from breast cancer in postmenopausal women. In women who were taking a placebo (dummy pill), the risk of death from breast cancer was 1.3 in every 10,000 women per year. In women who were taking combined HRT, the risk of death from breast cancer was 2.6 in every 10,000 women per year. Thus, the increase in risk is actually very small.

The study also found that these women were more likely to develop a more invasive type of breast cancer, involving the lymph nodes. In women who were taking combined HRT, the risk of developing invasive breast cancer was 42 in every 10,000 women per year. In woman who were taking the placebo, the risk was 34 in every 10,000 women per year, giving an absolute increase in risk of 8 cancers for every 10,000 women taking HRT for one year, or a risk of less than 1 per thousand.

To put this increased risk into perspective:

It is worth noting that the results of this study do not apply to women using oestrogen-only HRT, and that like other studies based on the WHI data, the results may not be applicable to women undertaking HRT closer to the time of menopause.

In June 2010, the US-based Endocrine Society issued a review of all the current evidence regarding the safety, benefits and risks of HRT. The review found that HRT offers significant benefits to women around the time of menopause suffering from moderate to severe menopausal symptoms. The North American Menopause Society recommends women who wish to use HRT do so at the lowest effective does for the shortest amount of time to treat moderate to severe menopausal symptoms. Both of these recommendations are consistent with the advice from Australian Menopause Society. For more information, go to http://menopause.org.au/consumers/position-statements/531-ams-us-endocrine-society-scientific-statement 

Professor Henry Burger, endocrinologist at the Jean Hailes Foundation for Women's Health says "The only new data in this publication, predictable from the earlier publications, was the slight increase in mortality associated with the breast cancers occurring in women on what are rather high doses of two specific hormones. It is not clear whether the figures are applicable to the lower doses of oestrogen in current use, or to women using a different progestin such as dydrogesterone. As stated in this, as well as earlier reports, there was no significant increase in breast cancer risk in the 75 per cent of women who had not previously used HRT before entering the trial, in whom one would not expect an increased mortality, although the authors do not provide the relevant numbers. The authors have previously also reported 30 per cent lower overall mortality in women treated between the ages of 50 and 59 years."

Content Updated 22 October 2010