The Million Women Study Fact Sheet

Here I will summarize the blog post below.  There is a study that was done with a million women in England and what has been concluded is that hormone replacement therapy (HRT) causes cancer.  It is conclusive; end of summary.  Feel free to read through the post below for more details. 

The Million Women Study was a national study of women’s health involving around one million UK women aged 50 and over. It was a collaborative project between Cancer Research UK and the National Health Service Breast Screening Program, with additional funding from the Medical Research Council, which aims to answer many outstanding questions about the factors affecting women’s health in this age group. The main focus of the study relates to the effects of hormone replacement therapy use, but the large size of the study means that a very broad range of health issues can be addressed.

What was the Million Women Study investigating?

The Million Women Study investigated how various reproductive and lifestyle factors affect women’s health. In particular, the study looked at how hormone replacement therapy affects a woman’s breasts and other aspects of her health. Other factors that were investigated were diet, childbirth, breastfeeding, vitamin and mineral supplement use, oral contraceptive use and family history of illness.

Who took part in the study?

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 Centers in the UK. At these centers, 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 program returned questionnaires and agreed to take part in the study—this excellent response means that over 1 in 4 women in the UK in the target age group participated in the study. It also means that the Million Women Study is the largest stufy of its kind in the world.

Who is involved in conducting the study? The Million Women Study is a nationwide study coordinated by experienced researchers based in Oxford. Funds for the study have been provided by Cancer Research UK, the National Health Service Breast Screening Program and Medical Research Council.

The Million Women Study was officially launched in 1997 and now involves over 60 National Health Service Breast Screening Centers nationwide. Thanks to staff working on the study and the enthusiasm of women throughout the UK, the study has now finished recruiting and 1.3 million women are taking part in the study.

First results on breast cancer and HRT use: Follow-up of over 1 million women in the Million Women Study has 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 author of this blog does not necessarily agree with this statement despite the results of the study.) The Million Women Study was able to show that this effect is substantially greater for combined (estrogen – progestin) HRT than for estrogen-only HRT; and that the effects were similar for all specific types and doses of estrogen and progestin, for oral, transdermal and implanted HRT, and for continuous and sequential patterns of use. Current users of estrogen – prgestagen HRT were at 2 fold increased risk of developing breast cancer, and current users of estrogen-only HRT at 1.3 fold risk. Use of HRT by women aged 50-64 in the UK in the past decade has resulted in an estimated 20,000 extra breast cancers.

Breast Cancer and hormone replacement therapy in the Million Women Study: Current use of HRT is associated with an increased risk of incident and fatal breast cancer; the effect is substantially greater for estrogen progestin than for other types of HRT.

HRT and Breast Cancer: Results of the Million Women Study

SOME kinds of hormone replacement therapy (HRT) have a much greater effect on a woman’s risk of breast cancer than others, according to landmark research published in the Lancet several years ago.

The Million Woman Study, funded by Cancer Research UK, the NHS Breast Screening Program and the Medical Research Council, confirms that current and recent use of HRT increases a woman’s chance of developing breast cancer and that the risk goes up with duration of use.

Current users of all types of HRT, including estrogen-only, combined estrogen – progestagen and tabooed, are at increased risk of breast cancer compared with women who have never used HRT.  But the risk is substantially greater for users of combined preparations of HRT than for women on the other types.

Scientists at the Cancer Research UK Epidemiology Unit in Oxford analyzed data from over one million women between the ages of 50 and 64.  Women joined the study between 1996 and 2001 and half were using HRT or had done so in the past.  The study included 9,364 cases of invasive breast cancer and 637 breast cancer deaths, registered over 2.6 and 4.1 years of follow-up respectrively.

Researchers found that post-menopausal women using combination HRT were twice as likely to develop breast cancer as non users (a 100 per cent increase), while risk increased by 45 per cent among users of tibolone and by 30 per cent among users of estrogen-only HRT.  These effects were shown to wear off within a few years of ceasing use.

For every thousand postmenopausal women who begin 10 years of HRT use at age 50, there will be five extra cases of breast cancer among users of estrogen-only HRT and 19 among users of estrogen-progestagen combinations.  that equates to 45,000 and 114,000 additional cases, respectively, in the United States.

So combined HRT causes four times as many extra breast cancers as estrogen-only.

The study also found that current users have a 22 per cent increased risk of death from breast cancer compared with women who have never used HRT.  The result was statistical significant.  There are a substantial number of extra deaths associated with HRT use.

Lead author Professor Valerie Beral, Director of the Cancer Research UK Epidemiology Unit, says: “We estimate that over the past decade use of HRT by UK women aged 50-64 has resulted in an extra 20,000 breast cancers, estrogen – progestin therapy accounting for 15,000 of these.

“Combined estrogen – progestin HRT is usually prescribed for women who still have a uterus, to avoid the increased risk of cancer of the uterus caused by estrogen-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 progestin against the lowered risk of uterine cancer.