ormone replacement therapy can triple the risk of breast cancer, the biggest ever study has found, following more than a decade of controversy.
Last year the National Institute of Health and
Care Excellence (Nice) changed guidance to encourage more doctors to prescribe HRT claiming too many menopausal women had been left suffering in silence.
HRT is used to treat uncomfortable symptoms of the menopause – such as hot flushes, migraines, disrupted sleep, mood changes and depression – by topping up the decreased levels of hormones produced by the body.
But doctors were reluctant to prescribe it after a study in 2002 suggested it could raise the risk of cancer, a claim later widely disputed.
Now new findings by the Institute of Cancer Research and Breast Cancer Now suggest the original risk had actually been underestimated.
A study of 100,000 women over 40 years found those who took the combined oestrogen and progestogen pill for around five years were 2.7 times more likely to develop cancer compared to women who took nothing, or only the oestrogen pill.
The risk rose to 3.3 times for women who took the drugs for 15 years or more.
Around 14 in 1,000 women in their 50s are expected to develop breast cancer, but that rises to 34 in 1000 for women taking the combined pill, the study suggests.
“Our research shows that some previous studies are likely to have underestimated the risk of breast cancer with combined oestrogen-progestogen HRT,” said study leader Professor Anthony Swerdlow, of The Institute of Cancer Research.
“We found that current use of combined HRT increases the risk of breast cancer by up to threefold, depending on how long HRT has been used.
“Our findings provide further information to allow women to make informed decisions about the potential risks and benefits of HRT use.”
Since then the number of women taking HRT has more than halved with around one in 10 eligible patients now using the drugs, approximately 150,000 women.
More recently a review by Imperial College and a 10-year study by New York University found no evidence of a link, adding further to the confusion and last year the National Institute for Health and Care Excellence (Nice) changed its guidance to encourage doctors to offer HRT claiming one million women were suffering in silence.
At the time Nice said that the cancer risk was 27 in 1,000 so the new research, which followed 100,000 women for 40 years, increases that risk by 54 per cent.
The health watchdog said that the new study should not change how doctors prescribed HRT.
We found that current use of combined HRT increases the risk of breast cancer by up to three fold, depending on how long HRT has been used
Professor Anthony Swerdlow, Institute of Cancer Research
Professor Mark Baker, director of the Centre for Guidelines at NICE, said: “As with Nice guidance this study recognises there is no increased risk of breast cancer with oestrogen-only HRT but the combined HRT can be associated with an increased risk of breast cancer.
“The guideline makes clear that menopausal women should be informed that the impact of HRT on the risk of breast cancer varies with the type of HRT used.
“The message from our guidance to women is clear – talk about the menopause with your clinician if you need advice on your symptoms - it’s very important to discuss the options to find what might help you.”
The new study also found that the risk declined when women stopped taking HRT and there was no danger at all for women only taking oestrogen, which accounts for half of all prescriptions.
Baroness Delyth Morgan, chief executive at Breast Cancer Now, said: “Whether to use HRT is an entirely personal choice, which is why it’s so important that women fully understand the risks and benefits and discuss them with their GP. We hope these findings will help anyone considering the treatment to make an even more informed decision.
“On balance, some women will feel HRT to be a necessity. But in order to minimise the risk of breast cancer during treatment, it is recommended that the lowest effective dose is used for the shortest possible time.
“The good news is that the increased risk of breast cancer begins to fall once you stop using HRT.”
Experts said that for many women the risks would be outweighed by the daily benefits to quality of life.
"HRT is an effective treatment for menopausal symptoms, particularly with the management of hot flushes,” said Dr Heather Currie, spokeswoman for the Royal College of Obstetricians and Gynaecologists (RCOG) and chairwoman of the British Menopause Society (BMS).
“Women need clear, evidence-based information to break through the conflicts of opinion and confusion about the menopause.
“For many women, any change in breast cancer risk is outweighed by the benefit on their quality of life, bearing in mind that there are many other factors that increase the risk of breast cancer, for example lifestyle factors."
The research was published in the British Journal of Cancer.
During the menopause the body levels of the hormones oestrogen and progestogen begin to fall which can lead to many uncomfortable symptoms. HRT replaces those hormones.
What are the benefits of HRT?
Various studies have shown that HRT prevents hot flushes., improves sleep, lessens aches and pains, improves mood and alleviates depressive symptoms, reduces the risk of osteoporosis, lowers cholesterol and reduces the risk of cardiovascular disease and colo-rectal cancer
Why is HRT linked to cancer?
Cancer growth is known to be stimulated by hormones so increasing levels could boost tumour growth. Some cancer drugs now work by targeting receptors on cancer cells to prevent hormones getting inside.
What is my risk of cancer if I take combined HRT?
The usual risk or cancer for a woman of menopausal age is around 14 in 1,000. The new study suggests that combined HRT raises that risk to 34 in 1,000.
Am I at risk of I take oestrogen only HRT?
No, there is no link between oestrogen only HRT and an increased risk of breast cancer.
Can I switch to oestrogen only?
Around half of women are already prescribed oestrogen only HRT but it is usually recommended for women who have already had a hysterectomy as it can raise the risk of womb cancer.
What should I do if I am worried about taking combine HRT?
Many women will feel the benefits outweigh the risks, but women who are concerned should talk to their GP.
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