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 by women aged 50-64 years in the UK over the past decade has resulted in an estimated 20,000 extra breast cancers, of which 15,000 are likely to be associated with oestrogen-progestagen HRT.
Valerie Beral comments: "Combined oestrogen-progestogen HRT is usually prescribed for women who still have a uterus, to avoid the increased risk of cancer of the uterus caused by oestrogen-only therapy. Since our results show a substantially greater increase in breast cancer with combined HRT, women need to weigh the increased risk of breast cancer caused by the addition of progestogen against the lowered risk of uterine cancer. Comparing the risks is by no means simple, and women may well want to discuss options with their doctor." (quote by e-mail; does not appear in published paper).
In an accompanying Commentary (p 414), Chris van Wheel from the University of Nijmegen, The Netherlands, discusses the implications for general practitioners and their patients who use HRT. He comments: "The problem is in those women who are already, often for a long time, taking HRT-estimated at between 20% and 50% of all women 45-70 years of age in the western population.
This group should discontinue HRT use as soon as possible. Discontinuing HRT should be suggested in as supportive a way as possible, because no one will benefit from panic or over-reaction: general practitioners need to use the opportunities arising from their regular contacts with patients taking HRT to discuss treatment-related risks, to give advice about stopping, and to offer alternative support. There is a great need for a public information campaign, led by the medical professions, stating the current evidence in clear but unsensational wording and encouraging HRT users to consult their general practitioner."
Media briefing * The lead authors will present the results of the study at an embargoed media briefing to be hosted by Cancer Research UK at 10.30 am Thursday 7 August UK time. Venue: 44 Lincolns Inn Fields, London WC2. Further information from Richard Hoey at Cancer Research Uks Press Office (details below).
Contact: Richard Hoey, Cancer Research UK Press Office, 61 Lincoln's Inn Fields, London WC2A 3PX, UK; T) +44-0-20-7061-8300/8308; M) +44-0-7050-26-4059; E) Richard.hoey@cancer.org.uk NHS Cancer Screening Programmes press office, Eldon House, 1 Dorset Street, London W1U 4BB, UK; T) +44-0-20-7535-9990; F) +44-0-20-7535-9995;E) screening@westminster.com
Professor Chris van Weel, Department of General Practice and Social Medicine, University of Nijmegen, Code 229-HSV, PO Box 9101 6500 HB Nijmegen, Netherlands; T) +31-24-361-6332/4; F) +31-24-354-1862; E) c.vanweel@hag.umcn.nl.
Journal
The Lancet