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Nov. 8, 2007 -- Women who use oral contraceptives have an increased risk of developing cervical cancer, but the risk drops quickly once the pill is stopped.
Taking oral contraceptives for five or more years was associated with a doubling of cervical cancer risk in the newly published study.
But risk returned to that of never-users within a decade of stopping oral contraceptives.
The new analysis of data from 24 worldwide studies is one of the most rigorous examinations of cervical cancer risk in oral contraceptive users ever conducted.
Epidemiologist Jane Green, MD, who led the study team, tells WebMD that the findings should be seen as good news for women who take the pill or have taken it in the past.
The study is reported in the Nov. 10 issue of the journal The Lancet.
"We have known that women on the combined estrogen pill are at increased risk [for cervical cancer], she says. "What we haven't known is what happens after they stop taking the pill. Now we know that the risk starts to fall pretty quickly and has gone away 10 years later."
The new analysis of published and previously unpublished data from studies involving more than 16,500 cervical cancer patients and 35,500 women without the disease helps to quantify the risk associated with oral contraceptive use worldwide.
Routine screening for cervical cancer in developed countries like the United States has led to dramatic reductions in incidence.
For every 1,000 women in more developed countries who use the pill between the ages of 20 and 30, the researchers estimated that less than one extra cancer (4.5 instead of 3.8 for never-users) can be expected by the age of 50.
In less developed countries, the risk was estimated to be 8.3 cases per 1,000 decade-long oral contraceptive users, compared with 7.3 cases for every 1,000 never-users of the pill.
The sexually transmitted human papillomavirus (HPV) is a major risk factor for cervical cancer, but having multiple childbirths is also considered a risk factor for the disease.
Because of this, any discussion of risk related to use of oral contraceptives must consider whether women end up having fewer babies because they take them, says Peter Sasieni, PhD, of London's Wolfson Institute for Preventive Medicine.
And since use of oral contraceptives reduces a woman's risk of developing ovarian and endometrial cancer, Sasieni and Green agree that benefits probably outweigh the risks for most women.
Both also agree that the new findings show the importance of regular cervical cancer screening for women who take the pill.
"Regular screening is important for all women, but especially for those taking oral contraceptives," Sasieni says. "A woman who has regular screenings can basically forget about the increase in risk."