Hormone replacement therapy and cardiovascular disease: the case for a randomized controlled trial

The menopause is associated with an increased risk of developing cardiovascular disease. Oestrogen may influence various metabolic pathways which contribute to the pathogenesis of cardiovascular disease, and observational studies suggest that in postmenopausal women oral oestrogen replacement therapy confers some protection against coronary heart disease and to a lesser extent against stroke. What is not clear is the magnitude of the cardioprotective effect and the overall balance of long-term benefits and hazards. Research is also required to establish the relative effects of oestrogen replacement therapy and combined or opposed hormone replacement therapy (HRT) where progestogen is added to counter the proliferative action of oestrogen on the endometrium. A large randomized controlled trial is the only way to provide accurate estimates of the cardioprotective effect of HRT and of other long-term benefits and hazards. Feasibility studies undertaken through the UK Medical Research Council (MRC) General Practice Research Framework show that such a trial is acceptable to patients and their doctors. Recruitment and withdrawal rates indicate that a trial of sufficient size to show a 25% reduction in cardiovascular disease with 90% power at the 1% level would be feasible. The full trial is costly and it is proposed that the UK collaborates with other countries in a major international trial to complement the Women's Health Initiative trial in the USA. Feasibility studies in Europe are underway, the design and scientific rationale for the trial have been approved by the UK MRC and it is hoped that recruitment to the full-scale trial can begin soon.