Women on hormone replacement therapy are at increased risk of ovarian cancer, a study of nearly one million postmenopausal British women suggests.

Prof. Valerie Beral of Cancer Research UK and her team concluded an extra 1,000 women died from ovarian cancer between 1991 and 2005 because they were using HRT.

Dr. Jonathan Lee says the study found women on hormone replacement therapy faced a subtantial increase in risk of ovarian cancer.
(CBC)

Those receiving HRT had a 20 per cent higher risk of developing ovarian cancer compared to those who never took the hormones. The risk increased the longer women were on the therapy, the team reports in Thursday's online issue of the journal The Lancet.

In Canada, 80 per cent of women diagnosed with ovarian cancer lose their lives. About 1,700 die annually.

The therapy also led to increases in incidence of breast and endometrial cancers compared to those who never used the hormones, the study's authors found.

The good news is that the increased risk for ovarian cancer tended to diminish within a few years of stopping HRT, the British researchers found.

HRT prescriptions fall

HRT, once a popular treatment for menopausal women, was linked to higher rates of breast cancer, heart attack and stroke in the 2002 Women's Health Initiative study in the U.S.

Last year, 5.5 million prescriptions were written for HRT in Canada, fewer than half of those written in 2001.

"If we looked at a random population of 2,500 women taking hormone replacement therapy, there would be one extra case of ovarian cancer, so that is a substantial increase in risk," said Dr. Jonathan Lee, a cancer researcher at the University of Ottawa.

Reduction in the use of HRT should translate into five per cent fewer cases of ovarian cancers and deaths in Canada, estimated Dr. Steven Narod of Women's College Research Institute in Toronto.

"With these new data on ovarian cancer, we expect the use of HRT to fall further," Narod wrote in a commentary accompanying the study. "We hope that the number of women dying of ovarian cancer will decline as well."

A study in Thursday's New England Journal of Medicine added to the evidence that HRT raises the risk of breast cancer, with rates of the disease falling nine per cent from 2001 to 2004.

There is still a role for HRT, which is effective in treating symptoms of menopause such as hot flashes. The key, doctors say, it to be selective about when and if to use it.