Women who take hormone replacement therapy (HRT) for the menopause, even for only a few years, may have an increased risk of developing ovarian cancer, a new study has found.

Ovarian cancer is commonly referred to as the ‘silent killer' because its symptoms can often be confused with other illnesses, such as gastrointestinal disorders. As a result, most patients are not diagnosed until they are in the advanced stages of the disease.

Almost 250,000 women worldwide develop the disease every year, including around 330 women in Ireland.

UK researchers carried out a detailed analysis of 52 studies involving almost 22,000 women with ovarian cancer living in Europe, North America and Australia. These studies represent almost all of the epidemiological evidence ever gathered on HRT use and the risk of ovarian cancer.

They found that women who use HRT for only a few years are 40% more likely to develop cancer of the ovaries compared to women who have never taken HRT.

"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," said the study's co-author, Prof Sir Richard Peto, of the University of Oxford.

Current European and World Health Organization (WHO) guidelines for HRT do not make any mention of ovarian cancer.

The researchers found that the greatest risk appeared to be among current or recent HRT users - within the last five years . However, even though the risk of cancer fell over time if treatment was stopped, those who had used it for at least five years still had an increased risk of developing ovarian cancer even 10 years later.

The researchers also noted that while there are four main types of ovarian cancer, this increase in risk was only seen in two types. However these are the two most common types - serous and endometriod ovarian cancer.

"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 worldwide guidelines," commented study co-author, Prof Dame Valerie Beral, of the University of Oxford.

Details of these findings are published in the journal, The Lancet.