Women on HRT, and their doctors, will want to re-evaluate treatment in light of new findings, writes Muiris Houston
The results of yesterday's prematurely released study into HRT will cause much debate in the medical profession and no little alarm among the many women who have been taking the drug combination in question.
On the face of it, the US Women's Health Initiative is a well-constructed study, deliberately designed to assess the long-term effects of hormone replacement therapy. It is a randomised, multi-centre trial of over 16,000 post-menopausal women who took oral HRT for an average of 5.2 years. It is the first primary prevention trial in which the use of post-menopausal hormones was compared with placebo [a "dummy" pill]. Overall, the results of the study are consistent with the growing body of research into the effects of combination HRT. The increased risk of breast cancer with duration of use has been noted in the past, albeit after 10 years of treatment rather than five.
The elevated risk of coronary heart disease was largely limited to the first year of therapy, a phenomenon noted in other trials. And the study's "good news" - that HRT reduces the risk of colon cancer and fractures - is also consistent with previous research.
The June edition of Clinical Evidence, the bible for evidence-based medical practice, says: "One large, well-designed trial of HRT versus placebo found no reduction of major cardiovascular events in post-menopausal women with established coronary disease" - a strong argument against using oestrogen and progestogen as as a preventive therapy.
Yesterday's study follows the recent Heart and Oestrogen/Progestogen Replacement Study, which also showed an elevated risk of cardiac disease in women during their first year on HRT. So clearly this is the death knell for the practice of using HRT to prevent heart disease or stroke.
However, it is the breast cancer risk that will frighten most women. While the absolute risk to an individual is small - of 10,000 women taking this particular form of HRT for a year, eight will develop an invasive breast cancer - the fact that the risk is now apparent after three years of treatment will cause concern.
Women on HRT, and their doctors, will want to re-evaluate treatment decisions in the light of this finding.
As always with medical research, there are caveats. The results of the WHI trial concern only one form of HRT taken in oral form.
There is a wide range of products on the market here which contain other types of oestrogen and progestogen, or which are given in a different formulation, such as a skin patch. We now need further studies into the long-term safety of these products.
The short-term use of HRT is not called into question by yesterday's results. Certainly its use for up to a year after menopausal symptoms begin would seem reasonable, provided the patient has no history of heart disease, clotting problems, breast cancer or other contra-indications.
None the less the initial reaction from gynaecologists last night was that the WHI was indeed a landmark study of good quality with the capacity to radically alter prescribing guidelines for HRT.