Women undergoing hormone replacement therapy face an increased risk of ovarian cancer, a review claims.

It found the risk rises by 40 per cent after five years’ use – the recommended maximum – compared to a woman who has never had the treatment.

The findings come from an analysis of 52 studies involving 21,488 ovarian cancer patients – mostly from America, Europe and Australia.

Study co-author Professor Sir Richard Peto, from Oxford University, said: ‘For women who take HRT for five years from around age 50, there will be about one extra ovarian cancer for every 1,000 users and one extra ovarian cancer death for every 1,700 users.’ 

The effect was the same for the two main types of HRT – containing oestrogen only, or oestrogen combined with a progestogen. 

Past use of oral contraceptives made no difference, say researchers, even though the pill protects against the disease.

The review was published in The Lancet medical journal and was carried out by the Collaborative Group on Epidemiological Studies of Ovarian Cancer, which compares results from multiple studies of the disease.

However despite the latest results, other experts warn that the dangers of HRT should not be exaggerated.

Professor Rod Baber from the University of Sydney – who is also president of the International Menopause Society – said a previous large trial found no increased risk of ovarian cancer after five years of HRT.

He added that the new analysis found the risk was very low in absolute terms. ‘My advice to women would be that this study at worst suggests a very small increase in risk with use of HRT,’ he said. 

‘This is no reason for them to stop taking their HRT. The benefits of HRT in their own individual case should be weighed up against this information and they should discuss this with their own doctor.’