drunkOvarian cancer is slightly more common among women who take hormone replacement therapy (HRT), even for short amounts of time, according to the largest analysis of the subject to date.

Researchers from the University of Oxford, who are partly funded by Cancer Research UK, found there was an increased risk of developing ovarian cancer in women who had used HRT for less than five years.

“Research had already shown an increased risk of ovarian cancer for women using HRT for longer than five years. But this new, comprehensive analysis shows there’s also a risk if you use HRT for less time than that,” said Fiona Osgun, health information officer from Cancer Research UK.

The study, published in The Lancet, combined and analysed the results from 52 different studies that, collectively, involved 21,488 women from North America, Europe and Australia. The findings revealed that women using HRT for just a few years were around 40 per cent more likely to develop ovarian cancer than women who had never used HRT – although the overall (absolute) risk remains small.

“For women who take HRT for five years from around age 50, there will be about one extra ovarian cancer for every 1000 users and one extra ovarian cancer death for every 1700 users,” said Professor Sir Richard Peto, co-author of the study.

While the increased risk of getting ovarian cancer decreased over time after stopping treatment, women who had used HRT for five years or more still had a slightly increased risk of the disease 10 years later. However, the study wasn’t able to make predictions about risk over a longer period of time. The treatment is already known to slightly increase the risk of breast cancer, and some forms of HRT can also affect the risk of womb (endometrial) cancer.

Professor Dame Valerie Beral, co-author of the study, said the study could influence current HRT guidelines. “The definite risk of ovarian cancer even with less than five years of HRT is directly relevant to today’s patterns of use – with most women now taking HRT for only a few years – and has implications for current efforts to revise UK and worldwide guidelines,” she said.

The study was funded by the Medical Research Council and Cancer Research UK.

Now available: an exclusive GM special report on the latest developments in ovarian cancer. Download your free copy today.