Women who take hormone replacement therapy are more likely to be diagnosed with ovarian cancer and to die of the disease, according to a study published in the Lancet* today.
Results from the Million Women Study, which is the biggest study of its kind in the world, show that over five years there is one extra case of ovarian cancer in every 2,500 women who take HRT. And for every 3,300 women who take HRT, there will be one additional death from ovarian cancer.
The researchers, who are largely funded by Cancer Research UK, estimate that use of HRT since 1991 has resulted in an extra 1,300 cases and 1,000 deaths from ovarian cancer.
The study also suggests that a woman's risk of ovarian cancer returns to a normal level within a few years of stopping HRT.
Ovarian cancer is the fourth most common cancer in women in the UK with almost 7,000 new cases each year. The five year survival rate for the disease is less than 30 per cent which reflects the fact that ovarian cancer is often diagnosed at a late stage.
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."
Previous results from the Million Women Study have linked the use of HRT with breast and endometrial cancer (cancer of the womb lining). Combined with ovarian cancer, these three diseases account for almost 40 per cent of all cancers in women in the UK and 25 per cent of cancer deaths.
The overall incidence of these three cancers in women who take HRT is 31 cases for every 1,000 women over five years. This compares with 19 cases in women who have never taken HRT.
The Million Women Study represents a quarter of all women aged 50 to 64 in the UK. This research involved nearly 950,000 women in that age group. Around a third of the women were taking HRT and a further fifth had taken it in the past. The women were followed up for an average of almost seven years.
The research showed that the risk of ovarian cancer was increased regardless of which kind of HRT the women were taking.
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 chose to take HRT should aim do so for clear medical need and for the shortest possible time."
Source: Cancer Research UK