Hormone replacement therapy (HRT) may actually cut the risk of breast cancer, a new study suggests, in a finding which could alleviate fears surrounding the treatment.
Millions of women in Britain face debilitating effects from menopause such as hot sweats, depression and sleep problems.
Yet doctors are often reluctant to prescribe HRT because previous studies have shown it increases the risk of breast cancer.
But new findings show that women who were only given oestrogen replacement, rather than the double hormonal treatment of progestin and oestrogen, actually cut their cancer risk by 23 per cent.
It is the equivalent of the chance of developing cancer falling from three women in 100 to two in 100.
“Menopausal hormone therapy with oestrogen plus progestin and oestrogen alone continues to be used by millions of women worldwide,” said lead author Dr Rowan Chlebowski, chief of Medical Oncology, at the University of California, Los Angeles (UCLA).
“Nonetheless, after nearly half a century, menopausal hormone therapy influence on breast cancer incidence and mortality remains unsettled, with discordant findings from prospective observational studies compared to findings from randomized clinical trials.”
Around 13 million women are menopausal or post-menopausal in Britain yet only one million currently take HRT, despite huge benefits.
In two randomised trials involving more than 27,000 women, those who received the two hormones saw their risk of breast cancer rise by 29 per cent compared to those on a placebo, while the chance fell for those on the single hormone.
Currently oestrogen-only HRT is only prescribed to women who have had a hysterectomy - an operation to remove the womb - because the hormone is known to increase the risk of womb cancer.
But 60,000 women undergo a hysterectomy every year in Britain and by the age of 60 one in five women have had the procedure, so tens of thousands of women could benefit from taking the oestrogen only drug.
The new findings may also open the door to more women choosing to have a hysterectomy so that they could safely take HRT afterwards.
Dr Melanie Davies, Consultant Gynaecologist, University College London Hospitals (UCLH), said: “The finding of benefit from oestrogen-only HRT is surprising.
“Oestrogen and progestin have opposite effects on the breast, so that standard combined HRT increases cancer risk but oestrogen-alone reduces risk.
“This adds to the information available for women considering HRT, and in particular can reassure women who have had a hysterectomy and take oestrogen.”
In 2015 guidance from the National Institute of Health and Care Excellence (Nice) said that too many women were suffering in silence because they were not being prescribed HRT and urged GPs to be more open about the benefits and risks.
Yet in recent years observational studies have continued to show an increased risk for both forms of the therapy, leading doctors to often discourage women from taking it.
In contrast, the new trials were randomised controlled experiments in which half the women were given placebo and half HRT, so are much higher quality, and likely to show the true picture.
And although the trials involved older forms of the treatment, the newer versions may even work better at protecting women, as they are more like the body’s own hormones. The findings were presented at the San Antonio Breast Cancer Symposium in Texas.