The Million Women Study is a study of women’s health analyzing data from more than one million women aged 50 and over conducted by UK researchers. It is a collaborative project between Cancer Research UK and the National Health Service (NHS), with additional funding from the Medical Research Council (UK). The study has abundantly fulfilled its aims of illuminating the answers to crucial questions about factors affecting the health of women in this age group, as its collaborators continue their frequent contribution to prestigious medical journals of what has become an impressive series of landmark medical papers.

One key focus of the study relates to the effects of hormone replacement therapy use on women's health. The study has confirmed the findings in the Women's Health Initiative(WHI) that women currently using HRT are more likely to develop breast cancer than those who are not using HRT.

Results from the Million Women Study, together with those of the WHI trial from the USA, have influenced national policy, including recent recommendations on the prescribing and use of hormone replacement therapy from the Royal College of Obstetricians and Gynaecologists and from the Commission on Human Medicines.

Study Design

The Million Women Study is a multi-centre, population-based prospective cohort study of women aged 50 and over invited to routine breast cancer screening in the UK. Between 1996 and 2001, women were invited to join the Million Women Study when they received their invitation to attend breast screening at one of 66 participating NHS Breast Screening Centres in the UK. At these centres, women received a study questionnaire with their invitation, which they were asked to complete and return at the time of screening. Around 70% of those attending the programme returned questionnaires and agreed to take part in the study, over 1 in 4 women in the UK in the target age group. The Million Women Study is the largest study of its kind in the world.

Aims

The Million Women Study was set up with the aim of recruiting 1,000,000 women in the UK into a cohort study, to provide answers to the following questions:

§  What effects do combined oestrogen and progestagen hormone replacement therapy (HRT) preparations have on breast cancer risk?

§  Are breast cancers detected at screening in women who have used HRT or oral contraceptives different in terms of size and invasiveness from the cancers detected in women who have never used these hormones?

§  How does HRT use affect the efficacy of breast cancer screening?

§  How does HRT use affect mortality from breast cancer and other conditions?


CANCER OF THE WOMB, ITS SYMPTOMS, DIAGNOSIS, PROGNOSIS, AND TREATMENT

Findings

HRT and Breast Cancer

Follow-up of over 1 million women in the Million Women Study confirmed findings from other recent studies that women currently using HRT are more likely to develop breast cancer than those who are not using HRT.Past users are not at increased risk. The study was able to show that this effect is substantially greater for combined HRT than for oestrogen-only HRT; and that the effects were similar for all specific types and doses of oestrogen and progestagen, for oral, transdermal and implanted HRT, and for continuous and sequential patterns of use. Current users of oestrogen-progestagen HRT were at 2 fold increased risk of developing breast cancer, and current users of oestrogen-only HRT at 1.3 fold risk. Use of HRT by women aged 50–64 in the UK in the decade from 1993-2003 resulted in an estimated 20,000 extra breast cancers.