Breast cancer risk from HRT 'underestimated'
The risks of hormone replacement therapy (HRT) may have been underestimated, experts have said.
Women taking combined HRT to combat the effects of the menopause are more likely to develop breast cancer, with risk increasing the longer it is used, the study found.
The new study, published in the British Journal of Cancer, found that those taking oestrogen plus progestogen HRT were 2.74 times more likely to develop breast cancer.
And those who had been using the combined HRT for 15 or more years had a 3.27 times increased risk, the study found.
But once HRT-use ended the increased risk returned to normal levels, the authors stressed.
Those taking oestrogen-only HRT did not have an increased risk, they found.
The findings were drawn from thousands of women taking part in the Breast Cancer Now Generations Study - a major study following more than 100,000 women for 40 years to investigate the causes of breast cancer.
Experts analysed data over six years from almost 40,000 menopausal women - 775 of whom developed breast cancer.
HRT is used to treat symptoms of the menopause - such as hot flushes, migraines, disrupted sleep, mood changes and depression - by replacing hormones lost through the menopause.
For around 10pc of women, symptoms can last for up to 12 years. The average age for menopause in the UK is 51. Around one-in-ten women use HRT during their 50s.
Research has shown that HRT increases the risk of breast and ovarian cancer, while links have also been made with stroke and heart attack.
But the authors of the latest study said that previous studies could have underestimated the risk of breast cancer because they did not use updated information on women's use of HRT over time. "Our research shows some previous studies are likely to have underestimated the risk of breast cancer with combined oestrogen-progestogen HRT," said study lead author Anthony Swerdlow, professor of epidemiology at The Institute of Cancer Research, London.
"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.
Commenting on the study, Dr Heather Currie, spokeswoman for the Royal College of Obstetricians and Gynaecologists (RCOG) and chairwoman of the British Menopause Society (BMS), said HRT is an effective treatment for menopausal symptoms, however, the risks and benefits are different for each woman. "Women need clear, evidence-based information to break through confusion about the menopause," she said.