Two recent, large studies looked at the links between hormone replacement therapy (HRT) and breast cancer. They found that prolonged use of HRT increases a woman’s risk of breast cancer.

The size of the risk varies with the type of HRT used and increases the longer HRT is taken. Once HRT is stopped the risk begins to reduce and after five years reaches the same level as in women who have not taken HRT.

There are three main types of HRT prescribed in the UK:

• oestrogen-only therapy
• combined therapy (oestrogen and progestogen)
• tibolone (Livial)

The following figures give some idea of the level of risk of breast cancer in women who have never taken HRT and with the different types of HRT.

Women who have never taken HRT

For every 1000 women aged 50, who never take HRT, 32 will develop breast cancer by the age of 65.

Women who take oestrogen-only HRT for 5 years

For every 1000 women aged 50, who take oestrogen-only HRT for the next 5 years, 33-34 will develop breast cancer by the age of 65.

So, this is an extra 1-2 cases for every 1000 women taking the HRT.

Women who take oestrogen-only HRT for 10 years

For every 1000 women aged 50, taking oestrogen-only HRT for the next 10 years, 37 will develop breast cancer by the age of 65.

So, this is an extra 5 cases for every 1000 women taking the HRT.

Women who take combined HRT for 5 years

For every 1000 women aged 50, 38 will develop breast cancer by the age of 65.

So, this is an extra 6 cases for every 1000 women taking combined HRT.

Women who take combined HRT for 10 years

For every 1000 women aged 50, 51 will develop breast cancer by the age of 65.

So, this is an extra 19 cases for every 1000 women, taking combined HRT.

Women who take tibolone

The figures for tibolone are less certain but probably the amount it increases the risk of breast cancer is in between that for oestrogen-only and combined HRT.

These results clearly show that taking HRT for 5 years or more does increase breast cancer risk and that long-term HRT use should be avoided if at all possible. Although in women of 50 years or over the benefits of short-term use of HRT to control distressing menopausal symptoms, may still outweigh any risks.

These figures only apply to women over the age of 50. So far, the evidence is that in younger women who have an early menopause, taking HRT up to the age of 50 does not increase the risk of breast cancer compared to other women of the same age who have not had their menopause.

If a woman over 50 who has been on HRT for more than 2 years stops HRT her risk of breast cancer gradually reduces. After 5 years her risk is the same as in women who have never taken HRT.

The current guidance from the Department of Health is

• for women under 50 years HRT may be used for treating menopausal symptoms and preventing bone thinning (osteoporosis)
• for women over 50 years HRT may be given as a short-term treatment for menopausal symptoms. However, the lowest possible dose should be prescribed for the shortest possible time, and the treatment needs to be reviewed with your doctor at least once a year

This answer can only give a general picture, and the risks and benefits of HRT vary from one woman to another. If you are concerned talk to your GP who can help you to weigh up the pros and cons in your personal situation.