A meta-analysis carried out by Oxford University claims that hormone replacement therapy increases the risk of ovarian cancer.

In the analysis, published in The Lancet researchers analysed 52 studies involving 21,000 women and found that even those who took it for less than five years raised the risk level. Although risk declined the longer ago use had ceased, about 10 years after stopping long-duration hormone therapy use there was still an excess of serous or endometrioid tumours.

The researchers said that “the increased risk may well be largely or wholly causal; if it is, women who use hormone therapy for five years from around age 50 have about one extra ovarian cancer per 1,000 users and, if its prognosis is typical, about one extra ovarian cancer death per 1,700 users”. They added that the findings that ovarian cancer risk is greatest in current users of hormone therapy, falls after use ceases, and varies by tumour type, “strongly suggest a causal relationship”.

The analysis notes that at present, the World Health Organisation, European and US guidelines about hormone therapy “do not mention ovarian cancer, and the UK guidelines (which are due to be revised) state only that risk may be increased with long-term use”.

Katherine Taylor, acting chief executive at Ovarian Cancer Action, said that “we welcome any new research which helps us to build on our knowledge [but] it’s important to remember though, that every woman is different and they may each have different risk factors”. She added that for example, “we know that a woman's genetic make-up can have a significant impact on her likelihood of developing ovarian cancer, particularly in the case of mutations in the BRCA1/2 genes. Knowing her BRCA status could affect a woman’s decisions around her health care. It could help her to decide whether HRT is the right path”.