Women who use oestrogen-only hormone replacement therapy (HRT) to relieve menopausal symptoms after a hysterectomy have a reduced risk of developing or dying from breast cancer.
This is the conclusion of a US study of around 7,500 women who took oestrogen-only HRT or a placebo for about six years then stopped.
Previous research indicates that the more common form of HRT, which contains both oestrogen and the hormone progesterone, increases the risk of developing breast cancer.
In this new study, around five years after stopping treatment, 151 women in the oestrogen-only HRT group developed breast cancer, versus 199 women in the placebo group, a difference of 23 per cent.
Women in the HRT group who did develop breast cancer were also 63 per cent less likely to die from the disease.
Oestrogen-only HRT is known to be linked to cancer of the womb and for this reason is only given to women who have undergone a hysterectomy.
The new results, published in The Lancet Oncology journal, come from the Women’s Health Initiative (WHI), a major US study of post-menopausal women launched in 1993.
The study showed that women who had oestrogen-only HRT had long-lasting protection against breast cancer.
But this potential benefit needs to be balanced against an increased risk of blood clots and strokes associated with HRT, say the researchers, who were led by Professor Garnet Anderson, from the Fred Hutchinson Cancer Research Centre in Seattle.
And women with a family history of breast cancer do not seem to benefit from the protective effects of oestrogen-only HRT.
The researchers said that the study does not support the use of oestrogen solely to reduce breast cancer risk.
Professor Jack Cuzick, a Cancer Research UK epidemiologist based at Queen Mary, University of London, said the results were important: “This is the first randomised controlled trial of oestrogen-only HRT and breast cancer risk, and is well designed. So although this study contradicts some research showing that oestrogen-only HRT moderately increases the risk of breast cancer, it shouldn’t be ignored. We need further research to clarify exactly how oestrogen-only HRT affects breast cancer risk in women of different ages and family histories.
“If a woman is considering starting or stopping HRT, or using it for a long time, she should discuss it with her doctor who can help weigh up the benefits and risks of different types of HRT and make the right choice based on her own circumstances.
“There are different types of HRT, and it’s clear that combined types increase the risk of breast cancer and other health problems. For women who’ve had a hysterectomy, oestrogen-only HRT is an effective short-term treatment for menopausal symptoms. But women taking it should use the lowest dose possible for as short a time as they need it.”
- Anderson, G. et al. (2012). Conjugated equine oestrogen and breast cancer incidence and mortality in postmenopausal women with hysterectomy: extended follow-up of the Women’s Health Initiative randomised placebo-controlled trial The Lancet Oncology DOI: 10.1016/S1470-2045(12)70075-X