A study in this week's issue of THE LANCET involving over a million women in the UK provides strong evidence that use of combination (progestagen-oestrogen) hormone replacement therapy (HRT) is associated with a substantially greater risk of breast cancer than oestrogen-only therapy. The study is also the first to report an increase in risk of death from breast cancer for HRT users compared with women who have never used HRT.

Previous research has highlighted the association between HRT and breast cancer. The Million Women Study lead by Valerie Beral and colleagues from Cancer Research UK's Epidemiology Unit, Oxford, UK, was set up to investigate the effects of specific types of HRT on incident and fatal breast cancer. Around a million UK women aged 50-64 years were recruited into this study between 1996 and 2001. Half the women had used HRT; 9364 breast cancers and 637 breast cancer deaths were registered after an average of 2.6 and 4.1 years of follow-up.

Current users of all types of HRT including oestrogen-only, combined oestrogen-progestogen, and tibolone (synthetic HRT) were at an increased risk of breast cancer compared with never users. The risk of breast cancer increased with increasing duration of HRT use; this effect appeared to wear off within a few years of stopping therapy. Current users were also at a 22% relative increased risk of death from breast cancer compared with never-users.

Use of combined oestrogen-progestogen therapy was associated with a substantially greater increase in risk than other types of HRT. For every 1000 postmenopausal women in developed countries who take HRT for 10 years, use of oestrogen-only HRT is estimated to cause an extra 5 breast cancers compared with 19 extra breast cancers with 10 years' use of combined oestrogen-progestogen. In other words, combined oestrogen-progestogen HRT causes four times as many extra breast cancers as oestrogen-only HRT. The investigators state that the use of HRT
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Contact: Joe Santangelo
j.santangelo@elsevier.com
212-633-3810
Lancet
7-Aug-2003

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