Apr 18, 2007
Figures from the Million Women Study suggest 1,000 extra women in the UK died from ovarian cancer between 1991 and 2005 because they were using HRT.
The researchers, writing in the Lancet, said HRT increased the risk of ovarian, breast and womb cancers.
Experts said current advice would not change and women should be on HRT for the shortest possible time.
Previous results from the Million Women Study, published in 2003, showed use of combined HRT doubles the risk of breast cancer.
The findings prompted recommendations that women weigh up the risks and benefits of HRT and take the smallest possible dose for the shortest possible time.
The new analysis of 948,576 postmenopausal women showed a 20% increased risk of developing and dying from ovarian cancer in HRT users, compared with those who had never used the treatment.
This translates to one extra case of ovarian cancer for every 2,500 women taking HRT and one extra death from ovarian cancer in every 3,300 users.
The increased risk was the same for all types of HRT.
Risk of ovarian cancer in women taking HRT returned to normal within a few years of stopping treatment.
Lead researcher, Professor Valerie Beral - director of Cancer Research UK's epidemiology unit at the University of Oxford - said: "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.
"This study, along with our previous research, clearly demonstrates the cancer risks of taking HRT."
The team said overall ovarian, breast and womb (endometrial) cancer accounted for 40% of all cancers diagnosed in UK women and that the total incidence of the three is 63% higher in those taking HRT.
Professor John Toy, Cancer Research UK's medical director said: "This study clearly shows that taking HRT increases a woman's chance of getting ovarian cancer and her chances of dying from the disease.
"Considering this alongside the increases in risk for breast and endometrial cancer, women should think very carefully about whether to take HRT.
"And women who choose to take HRT should aim do so for clear medical need and for the shortest possible time."
And Annwen Jones, chief executive of leading charity Ovarian Cancer Action said the study provided further evidence of the risks linked to HRT.
In the UK the number of HRT users fell from two million in 2002 to one million in 2005, according to data from the General Practice Research Database.
Professor Stephen Franks, professor of reproductive endocrinology at Imperial College London, said: "My general view is that patients with symptoms of the menopause should be treated, but it's always a balance of risks and benefits."
He added that it was advisable not to take any medicine longer than needed.
A spokesman for the Medicines and Healthcare products Regulatory Agency said the new data was being studied by an expert group but the advice was unlikely to change, and HRT remained an effective treatment for the short-term relief of menopausal symptoms in the majority of women.
He added: "Any woman on HRT who is concerned should discuss her need to continue treatment with her doctor."