Women who take the contraceptive Pill over many years greatly increase their risk of cervical cancer, a major scientific study has shown.

Researchers found that the risk of contracting cancer doubled after ten years or more of Pill use, while women who took the Pill for five years or less had a 10 per cent increased risk. The findings, which came from 12,500 women with cervical cancer in 24 countries, are robust enough to remove any doubts about a link between oral contraceptives and cervical cancer.

However, doctors emphasised that it was still unknown to what extent the risk remained after a woman stopped taking the Pill. About 3,200 women have cervical cancer diagnosed each year in Britain. The lifetime risk of a cervical cancer diagnosis is 1 in 80.

Amy Berrington, from Cancer Research UK’s Epidemiology Unit at the Radcliffe Infirmary, Oxford, said that more work was needed to determine the longer-term risks.“However, the public health implications of these findings largely depend on whether this risk remains long after use of hormonal contraceptives has stopped and this cannot be properly evaluated from published data. There is some evidence to suggest that the risk may drop after women stop using the Pill but further research is needed to confirm this.”

She said that the World Health Organisation was funding an investigation to provide answers to that part of the puzzle.

The scientists from Cancer Research UK and the International Agency for Research on Cancer in France reviewed data from 28 published studies in 24 countries, including Britain and the US. Their findings, reported today in The Lancet, say that the longer women use the Pill, the greater the risk of developing cervical cancer.

They found that women who used the pill for five years or less had a 10 per cent increased risk of cervical cancer when compared with women who had never taken it. This increased risk rose to 60 per cent with five to nine years of use and doubled with ten years of use or over.

A similar pattern of increased risk was seen when researchers took into account other factors that could influence cervical cancer risk, such as smoking, their number of sexual partners, whether they had previously attended cervical cancer screening and whether they used barrier methods of contraception.

Infection by some types of sexually transmitted human papilloma virus (HPV) is thought to be the most important trigger for cervical cancer.

But whether women infected with HPV go on to develop the disease may be influenced by other factors, such as using hormonal contraceptives.

Lesley Walker, director of information at Cancer Research UK, said: “Previous studies have shown that the Pill may increase the risk of breast cancer and lower the risk of ovarian cancer. Now the new data suggests that it could raise the risk of cervical cancer.

“It’s vitally important that we continue to gather all the information we can on cancer risk and the Pill, so women can make fully informed choices about contraception. We would continue to stress the importance of cervical screening whether or not women use the Pill.”

Anne Weyman, chief executive of the Family Planning Association, said that for the vast majority of women the benefits of using the Pill greatly outweighed the risks. “The Pill is highly effective in preventing pregnancy and reduces the risk of both cancer of the ovaries and womb,” she said.

She pointed out that HPVs were found in more than 99 per cent of cases of cervical cancer and remained the most important risk factor. “These findings suggest that the longer a woman uses the Pill, the greater her risk of developing cervical cancer, but the UK’s national cervical screening programme means the absolute risk of developing cervical cancer remains very low,” she said.

“It is essential that women continue to take up the offer of regular cervical smears to safeguard their sexual health.”

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