HRT was back in the spotlight last night after an Oxford study found it raised the risk of breast cancer by a third.
Researchers said women aged 50 to 69 were 32 per cent more likely to get the disease if they had taken the most common form of the hormone replacement therapy for at least five years.
The danger was twice as high for patients on the treatment for a decade.
The Oxford team said however that the overall risk was still small – and doctors said the benefits often outweighed the risks.
Based on 58 global studies, the research suggested that HRT causes around one in 20 cases of breast cancer – nearly 3,000 a year in Britain.
The Oxford team said however that the overall risk was still small – and doctors said the benefits often outweighed the risks
The extra risk lasted for ten or more years after women stopped the treatment. Only those on it for less than a year were found to have no greater or little chance of cancer.
The study showed that 8.3 per cent of patients taking HRT for five years developed breast cancer, compared with 6.3 per cent of women not on the treatment.
Its authors said they were concerned that GPs were telling women not to worry about the risks.
Without wanting to be ‘unduly alarming’, they suggested the NHS should update its guidelines.
Doctors urged women not to panic however, saying the benefits of relieving night sweats, depression and hot flushes often outweighed the risks.
Others pointed out that most HRT patients would start sleeping better and exercising more, improving their health and lowering their background cancer risk.
Published in the Lancet, the research was by the same Oxford University researchers involved in one of the two original – and much smaller – studies in 2002 and 2003 that first raised the breast cancer link.
It confirmed these original findings and showed the risk persisted much longer than thought.
Author Professor Valerie Beral said: ‘This study has brought together all worldwide evidence.
‘It shows a persistent risk of breast cancer for ten to 15 years even after people stop taking menopausal hormone therapy, this was not known about before.
‘Previous estimates of risks are approximately doubled by the inclusion of the persistent risk after use of the hormones ceases.
‘We are concerned GPs are telling women they don’t need to worry about it.’
Co-author Professor Richard Peto said: ‘We don’t want to be unduly alarming but we don’t want to be unduly reassuring.
‘Guidelines should be reconsidered in light of accurate information. Currently the risk of HRT is misrepresented.
‘The NHS Choices website talks of a breast cancer risk of two per thousand women but actually it is 20 per thousand.’
Baroness Delyth Morgan, of Breast Cancer Care and Breast Cancer Now, said the study provided important new information.
She added: ‘Taking HRT is a really personal decision, and it’s vital that everyone fully understands the benefits and risks, discusses them with their GP and is supported to make the decision that’s right for them.
‘These robust findings also tell us more about the long-term impact of different types of HRT on breast cancer risk, and, rather than causing concern, we hope they will help anyone considering HRT treatment to make an even more informed decision.
‘On balance, many women will feel HRT to be a necessity, as it can be really effective in helping them control debilitating menopausal symptoms such as hot flushes.
‘In order to minimise the risk of breast cancer, it is normally recommended that the lowest effective dose is used for the shortest possible time.’
Dr Louise Newson, a GP who specialises in the menopause, said: ‘The very small increased breast cancer risk needs to be put in context balanced against the health benefits of HRT. Menopause symptoms can be debilitating and HRT transforms the lives of thousands of women.
‘I see a lot of patients who have had breast cancer and chemotherapy but still choose to take HRT because of the benefits, which include protecting against osteoporosis.
‘Most women on HRT will start sleeping better and exercising more, therefore they improve their overall health and lower their background risk of cancer.’
Professor Janice Rymer, of the Royal College of Obstetricians and Gynaecologists, said patients should be warned of the small increase in risk of breast cancer so they can weigh these up against the costs and benefits.
‘Unfortunately, many women are still suffering in silence and are reluctant to seek advice and support due to concerns around the risks of breast cancer associated with HRT,’ she said.
‘These findings should not put women off taking HRT if the benefits – such as protection of bones and decrease in cardiovascular risk – outweigh the risks.
‘To put the risk into context, a woman has greater risk of developing breast cancer if she is overweight or obese compared to taking HRT.’
Professor Martin Marshall of the Royal College of GPs said: ‘We would urge patients not to panic as a result of this research, and to continue taking HRT as it has been prescribed to them – and we would urge prescribers to do so as normal, until clinical guidelines recommend otherwise.’
The extent to which women rely on HRT has been shown by shortages – revealed by the Mail – that have left patients scrambling to get supplies, with some even buying from abroad.
Several hundred thousand British women take the treatment in gels, patches or pills.
Sarah Branch, of the Medicines and Healthcare products Regulatory Agency, said women who have used HRT should be vigilant about signs of breast cancer.
She added: ‘No medicine is completely without risk, but it is important for women to be able to make an informed decision about the risks and benefits.’