Women who have been taking hormone replacement therapy for many years run an increased risk of breast cancer, according to a new study involving over one million women.

Previous research has highlighted the link between long-term use of hormone replacement therapy (HRT) and breast cancer. A new study, from Cancer Research UK's Epidemiology Unit in Oxford, reinforces this finding. It is also the first to show an increased risk of death from breast cancer among those who are on HRT compared to that among women who have never used it.

Around one million women in the UK - of whom about half used HRT - were recruited between 1996 and 2001. Current users of all types of HRT were found to be at increased risk of breast cancer compared to never-users. The risk increased with duration of HRT use and the current users also had a 22 per cent increased risk of dying from breast cancer compared to the never-users.

Combined estrogen-progesterone therapy was riskier than estrogen only therapy. For every 1000 postmenopausal women taking estrogen-only HRT for ten years, there would be about five extra breast cancers, compared to 19 extra cases in those taking combined HRT. The researchers estimate that use of HRT by women aged 50 to 64 in the UK over the past decade has caused an extra 20,000 breast cancers. This is a wake-up call for women who've been using HRT for some time. Panic and over-reaction would be inappropriate, but women in this position should consider consulting their doctor over continued use of HRT.

Source

The Lancet 9th August 2003