Hormone replacement therapy -- reviewing the evidence

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HRT has been used increasingly across western populations since the early 1990s--an estimated 20 million women in western countries were using HRT at the end of the past decade. Around a third of women in their fifties in the UK use HRT for an average of five years, with a similar proportion in the rest of Europe. The impact of HRT on health outcomes has been widely debated, with suggestions that HRT use may increase the risk of certain cancers--notably breast cancer--while also being protective against osteoporosis and coronary heart disease.

Valerie Beral and colleagues from Cancer Research UK's Epidemiology Unit, Oxford, UK, reviewed the existing data on the effects of HRT on seven life-threatening conditions--largely based on data from four randomised trials, one involving an oestrogen-only treatment, the others using a combined oestrogen/progestagen combination--to provide an up-to-date analysis of the long-term effects of HRT use.

Evidence from the four HRT trials (which included over 20,000 women followed up for around five years) showed that HRT users are at an increased relative risk of breast cancer, pulmonary embolism (blood clot in the lung), and stroke, compared with women given placebo.

HRT was found to be protective against colorectal cancer and hip fracture. There were no significant differences in the risks of endometrial cancer or coronary heart disease, and not enough data to assess the relationship between HRT use and rarer diseases such as ovarian cancer. They estimated that for healthy women in their fifties, use of HRT for five years would cause an extra breast cancer, stroke, or pulmonary embolism in 6 in every 1000 users, but reduce the incidence of colorectal cancer and hip fracture by 1.7 in every 1000--giving on balance an overall increase in one of these conditions of 4.3 out of every 1000 HRT users (1 in 250). For women in their sixties, the overall increase is 6.5 in every 1000 HRT users (1 in 150). Breast cancer was the most prominent negative health outcome among users in their fifties, which shifted to cardiovascular disease among women in their sixties.

Valerie Beral comments: "These estimates provide a rough guide to the likely overall change in the incidence of these conditions over a 5 year period for typical healthy HRT users in western countries. Each woman would, understandably, give different weight to the importance of each condition, as well as to the relief of menopausal symptoms."

Contact:
Professor Valerie Beral,
c/o Cancer Research UK Press Office

Sally Staples,
Cancer Research UK,
61 Lincoln's Inn Fields, London WC2A 3PX, UK;
T) +44 (0)20 7061 6045;
F) +44 (0)20 7935 1546;
E) sally.staples@cancer.org.uk