A 14-year study of 212,000 women found that those who had used oestrogen-only replacement therapy (HRT) for ten years or more had doubled their risk of ovarian cancer. The increased risk remained even in women who had come off HRT 29 years earlier.

The mechanism was uncertain but other studies noted that reduced levels of gonadotrophin endocrines, which occurs during oestrogen-only HRT, had been linked to higher risks of ovarian cancer.

A US study of 46,000 women confirmed that those that took the oestrogen-only form of HRT for more than ten years had doubled their risk of developing ovarian cancer. The risk reduced with time off the therapy.

Ovarian cancer generally affects about 1.7% of the female population so, even doubled, is still quite small. A separate review of HRT research concluded that it also increased the risk of breast cancer in women under 70 from 4.5% to 4.7%.

The researchers noted that:

• HRT had been found to reduce the risk of heart disease by a greater extent

• little work had been carried out out on the risks from the newer forms of HRT which combine oestrogen and progestogen