LONDON: The risk of breast cancer from hormonal replacement therapy (HRT) for the menopause is double what women are currently being told, according to a major piece of research, By Nicola Slawson writes for Huffpost
However, Breast cancer experts were quick to point out that the increase in risk is relative and actual numbers are small, and that other factors have greater risk than HRT.
The increased risk of breast cancer from the hormone therapy lasts more than a decade after treatment stops, the researchers at the University of Oxford also found.
The researchers said that if the associations are causal, this means HRT (also known as MHT) use has already caused around one million breast cancers in western countries – one-twentieth of the total since 1990.
The global analysis used data from more than 100,000 women with breast cancer from 58 epidemiological studies worldwide. The researchers found that all types of MHT, except topical vaginal oestrogens, were linked to an increased risk of breast cancer.
The risks were greater for users of oestrogen-progestagen hormone therapy than for oestrogen-only hormone therapy. Prior to the release of the study, Cancer Research published figures about breast cancer risk, which give some context to the new findings.
It suggests 2% of breast cancer cases in the UK are caused by post-menopausal hormones, 8% of breast cancer cases in the UK are caused by being overweight and or obese, 8% of breast cancer cases in the UK are caused by alcohol drinking and 5% of breast cancer cases in the UK are caused by not breastfeeding.
The Oxford University researchers calculated that one million out of the 20 million breast cancers in western countries since 1990 may have been caused by menopausal hormone therapy. There are about 12 million users of the treatment in Western countries – about six million in North America and six million in Europe, including one million in the UK.
Women tend to begin HRT at around the time of the menopause, when ovarian function ceases, causing symptoms including hot flushes and discomfort.
Although regulatory bodies in Europe and the USA recommend HRT be used for the shortest time that is needed, some clinical guidelines recommended less restrictive prescribing. About five years of use is now common.
Co-author Professor Valerie Beral from the Nuffield Department of Population Health, University of Oxford, said: “Our new findings indicate that some increased risk persists even after stopping use of menopausal hormone therapy. “Previous estimates of risks associated with use of menopausal hormone therapy are approximately doubled by the inclusion of the persistent risk after use of the hormones ceases.”
She added: “Before all we knew was that the risk was increased when they used, the belief was that it went away when they stopped. “The main finding is that we now know the long-term effects, that the risk persists for more than a decade after stopping.”
The authors found that 108,647 women developed breast cancer at an average age of 65 – and almost half of these had used HRT. For women in western countries who have never used HRT, 6.3 women in every 100 on average go on to develop breast cancer between 50 and 69. This was for those who took the treatment for five years, starting at age 50.