Women who take hormone replacement therapy (HRT) are at greater risk of being diagnosed with ovarian cancer, a new study has concluded.
HRT users are also more likely than others to die of the disease, according to research published in the Lancet medical journal.
Researchers funded by Cancer Research UK estimate that the use of HRT resulted in an additional 1,300 women in Britain contracting ovarian cancer between 1991 and 2005, of whom 1,000 died.
It is also claimed that over a five year period one extra case of ovarian cancer is diagnosed for every 2,500 women who take HRT, while use of the therapy is thought to be responsible for causing one additional death from the disease among every 3,300 women who take it.
The study is based on the latest findings from the Million Women Study, a national survey of health in females aged over 50 in Britain.
Scientists examined almost 950,000 women for the research, with participants representing a quarter of all females aged between 50 and 64 in the UK.
They found that the risk of contracting ovarian cancer increased regardless of which type of HRT women were taking, while their chances of being diagnosed with the disease were shown to return to a normal level within a few years of ceasing to use the treatment.
Previous results from the Million Women Study have linked HRT to an increased risk of breast cancer and endometrial cancer, which affects the lining of the womb.
Lead researcher and director of Cancer Research UK’s epidemiology unit at Oxford University, professor Valerie Beral, described the latest findings as "worrying".
"The results of this study are worrying because they show that not only does HRT increase the risk of getting ovarian cancer, it also increases a woman's risk of dying of ovarian cancer," she said.
"This study, along with our previous research, clearly demonstrates the cancer risks of taking HRT."
Ovarian cancer is the fourth most common cancer in women in the UK with almost 7,000 new cases diagnosed each year.
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