You always think twice before giving HRT to women

Dr Sally Hope

However, the oestrogen-only form of the treatment has long been associated with an increased risk of uterine cancer.

To reduce this risk, doctors often combine the use of oestrogen with another female sex hormone, progestin.

However, a study by scientists from the Karolinska Institute in Sweden have found that this practice may increase the risk of ovarian cancer.

They compared data on 655 women with epithelial ovarian cancer with that from 3,899 cancer-free women.

They found that oestrogen-only HRT increased the risk of ovarian cancer by 43%.

However, the increased risk associated with a combination of the two sex hormones was even higher - 54%.

This risk was only associated with the on-off use of progestins.

If the hormone was given each day, then women had no increased risk of ovarian cancer at all.

Still a small risk

Overall, the risk of women who take HRT developing ovarian cancer is still small.

In the Swedish study, one out of 100 women between the ages of 50 and 75 will develop ovarian cancer regardless of HRT use.

Consequently, the authors do not recommend changing current prescribing practices.

They said the risk must be balanced against the potential benefits, such as reducing the risk of osteoporosis and heart disease.

This study adds to our overall knowledge of the balance between risks and benefits of taking HRT

Kate Law Cancer Research UK

However, they said: "If our findings are replicated it would be valuable to consider the epithelial ovarian cancer risk increase associated with the use of certain HRT regimens, especially given the prevalence of HRT use and the poor prognosis of epithelial ovarian cancer."

Dr Sally Hope, an Oxford GP and chairwoman of the Primary Care Gynaecology Group, told BBC News Online that the stop-start use of progestin stimulated the ovarian tissues.

However, a constant dose had the opposite effect. This was why women at high risk of ovarian cancer are prescribed the continuous progestin dose contraceptive pill.

She said: "Nobody has focused on the impact of HRT on ovarian cancer before. You always think twice before giving HRT to women, but that is because of the increased risk of breast cancer, which is far more significant."

'Talk to GP'

Kate Law, from Cancer Research UK, told BBC News Online: "This study adds to our overall knowledge of the balance between risks and benefits of taking HRT.

"There was a slight increase in the risk of ovarian cancer, but that has to be balanced against the known benefits of HRT, which include a reduction in risk of osteoporosis and heart disease.

"Women that are taking HRT or are considering it should discuss any concerns they may have with their GP."

The research is published in the Journal of the National Cancer Institute.