Women who take hormone replacement therapy (HRT) for more than 10 years double their risk of ovarian cancer, American researchers have found.

Women who take hormone replacement therapy (HRT) for more than 10 years double their risk of ovarian cancer, American researchers have found.

A study of 46,000 women on HRT found the risk increased with length of use but declined again when women stopped taking it.

The finding adds to research showing HRT carries a small increased risk of cancer of the breast, the endometrium (lining of the womb) and now of the ovaries.

However, HRT is also believed to reduce the risk of heart disease, which is likely to be much greater than the slight increase in cancer risk. HRT also protects the bones, reducing the risk of the bone thinning disease, osteoporosis.

In the latest study, researchers from the American Cancer Society in Atlanta point out that ovarian cancer is rare, affecting 1.7 per cent of the population, so a doubling of the risk only increases it to 3.4 per cent.

Their research, published in the Journal of the American Medical Association, looked only at women using oestrogen-based HRT.

Newer types of HRT include both oestrogen and progestogen and the risks associated with this type of HRT is unknown.

The women were among more than 200,000 recruited in the early Eighties for a study of cancer prevention. The researchers followed the 46,000 who were either taking HRT or had recently taken it for 14 years, until 1996.

They found that 944 women developed ovarian cancer. Those using HRT in 1982 had a 51 per cent higher risk of developing the disease. Those who used it for 10 or more years had a 120 per cent increased risk.

The researchers say that further large studies are needed to test their findings and to examine whether oestrogen combined with progestogen has the same effect.

A review based on 51 studies of HRT in 21 countries published in The Lancet in 1997 concluded there was a small increased risk of breast cancer in women taking HRT.

The risk amounted to two additional cases in every 1,000 women aged under 70, on top of the 45 cases that would be expected.

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