BRITAIN: Women who use a certain type of hormone replacement therapy are twice as likely to develop breast cancer as those who do not use any form of HRT at all, new research shows.
The study - published yesterday in the British medical journal The Lancet - of more than one million participants, found that post-menopausal women using the combined oestrogen-progestagen treatment were at a greater risk than those using other types of HRT.
Research found the risk increased by 45 per cent among users of tibolone, another form of the treatment, and by 30 per cent among users of oestrogen-only HRT.
The study showed that if a woman stopped taking HRT, within a few years her risk of developing breast cancer dropped back to that of non-users. In light of the study, Britain's Committee on Safety of Medicines has reviewed data and written to all health professionals.
Their advice, while not going as far as saying that women should stop taking HRT, is that doctors should carefully discuss with their patients the risks and benefits of treatment and review each case individually.
They said the results of the study did not mean any urgent changes to women's treatment were necessary.
Dr John Toy, medical director of Cancer Research UK, said while other reports had shown the risk of breast cancer increased in women taking HRT, the "vast" new study gave an accurate picture of the size of the effect.
"On a national scale, with so many women taking HRT, the number of extra cases of breast cancer has been quite large, but the increased risk does start to fall on stopping treatment. A woman wanting to take HRT for a long time would be extremely wise first to consider carefully the findings of this large study and other relevant research," Dr Toy said.
Cancer Research UK's Epidemiology Unit in Oxford monitored more than one million women between the ages of 50 and 64 who joined the study between 1996 and 2001. Half the women were using HRT or had done so in the past.
After 2.6 years of follow-up, 9,364 cases of breast cancer were found. After 4.1 years, 637 breast cancer deaths were registered among all the women studied.