Perhaps the most significant worry that most women have when considering whether or not to take Hormone Replacement Therapy (HRT) is the possible increased risk of breast cancer. Breast cancer is an oestrogen-dependent cancer and constitutes approximately 25% of all female cancers, therefore any woman who has early menopause and does not take any oestrogen supplementation will actually reduce her risk of developing breast cancer in later life.

Currently, about one woman in thirteen will develop breast cancer before the age of 75 and if there is a family history (sister or mother with the disease) the risk is increased to one in eight. Much of the initial data about the link between breast cancer and oestrogen supplementation has been taken from trials and studies based on the contraceptive pill.

To date there have been over forty studies looking at the link between HRT and breast cancer and there has been no consensus about the results. However, a meta-analysis of the studies estimates that there is no increase in risk when HRT is taken for up to five to ten years. If the length of treatment is extended to eight to fifteen years the increase appears to be about 25 – 30%.

Despite the worries over an increase in risk, it should be noted that these studies have taken place looking at women who had taken HRT following a natural menopause. Women who have an early surgical menopause would have naturally been producing oestrogen and its’ supplementation is simply replacing what they would normally produce.

Studies have also indicated that those women who do develop breast cancer whilst using HRT have a better prognosis and there is a decrease in the death rate compared to those who have not taken the supplements, however, this could be due to the fact that the women and their GP’s are more aware and will be more vigilant about checking their breasts regularly.
Factors to consider include:

  • previous history of oestrogen-dependent cancers
  • family history of cancer
  • starting menstruation before the age of eleven
  • not having a child or having your first child after the age of 30
  • being overweight
  • women who have diets high in fat and low in fibre also have higher levels of oestrogen in the blood

The million women study

The Million Women Study has recently finished its study into the effects of HRT on more than one million women and is currently undertaking an analysis of the research data. Initial results indicate that the current use of hormone replacement therapy (HRT) increases the incidence of breast cancer.

1,084,110 UK women aged 50-64 years were recruited into the Million Women Study between 1996 and 2001. They provided information about their use of HRT and other personal details and were followed up for cancer incidence and death.

The researchers found that half the women had used HRT; of the study sample there were 9364 cases of invasive breast cancers and 637 breast cancer deaths were registered after an average of 2.6 and 4.1 years of follow-up, respectively. These results seem to indicate that current users of HRT at recruitment were more likely than never users to develop breast cancer (by 1%) and to die from it by (1.22%).

However, previous users of HRT were, not at an increased risk of incident or fatal disease. The researchers did note that the incidence was significantly increased for current users of preparations containing oestrogen only, but that the magnitude of the associated risk was substantially greater for oestrogen-progestogen than other types of HRT. Results varied little between specific oestrogens and progestogens or their doses; or between continuous and sequential regimens.

In current users of each type of HRT the risk of breast cancer increases with increasing total duration of use. 10 years use of HRT is estimated to result in five additional breast cancers per 1000 users of oestrogen-only preparations and 19 (18-20) additional cancers per 1000 users of oestrogen-progestogen combinations. You can find out more about the results and analysis at the Million Women website.

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