A woman's risk of developing cervical cancer increases the longer she takes oral contraceptives, according to a study published in today's issue of the Lancet, BBC News reports (BBC News, 4/4). Researchers from Cancer Research UK's Epidemiology Unit in Oxford, England, and the International Agency for Research on Cancer in Lyon, France, examined 28 studies -- half of which were conducted in developing countries and half of which were conducted in the United States or Europe -- that included 12,531 women with cervical cancer. Researchers combined data from the studies to examine the link between invasive and non-invasive cervical cancer and the duration and time since last use of hormonal contraceptives (Smith et al., Lancet, 4/5). Researchers found that women who had used oral contraceptives for less than five years had a 10% increased risk of cervical cancer, compared with women who had never taken birth control pills; women who had taken the pills for five to nine years had a 60% increased risk; and women who had taken the pill for 10 years or longer had twice the risk of developing cervical cancer (Reaney, Reuters, 4/3). Researchers also compiled data separately from the 12 studies -- which included approximately 3,000 women -- that restricted analysis to women who tested positive for human papillomavirus, which is known to cause the majority of cervical cancer cases. The researchers found the same pattern of increasing risk with longer oral contraceptive use even when a woman's HPV status, smoking status, number of sexual partners, use of barrier contraception and access to regular Pap tests were taken into account. The researchers said that the findings demonstrate that the relative risk of cervical cancer becomes larger with the increasing duration of oral contraceptive use "in virtually every way that data were examined." The researchers state that more studies are necessary to determine if the findings are "biased or confounded" by HPV infection, which they said is "likely to be the most important cause of cervical cancer" (Lancet, 4/5). The researchers said that "some evidence" exists to suggest that a woman's increased risk of the cancer drops after she discontinues taking the pills but it is unclear (Boseley, Guardian, 4/4). Dr. Amy Berrington, one of the researchers, said that the next step is to further investigate this possibility, adding that the results of that research would be available sometime next year (Reuters, 4/3).

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The U.K. Family Planning Association said that despite the study's findings, the benefits of the birth control pill "greatly outweig[h]" the potential increase in cancer risk, according to London's Guardian. FPA CEO Anne Weyman added that the pill is "highly effective" in preventing pregnancy and can reduce a woman's risk of ovarian and uterine cancers. Lesley Walker of U.K.-based Cancer Research said there have also been studies indicating that oral contraceptives could raise a woman's risk of breast cancer, adding, "It's vitally important to gather all the information we can on cancer risk and the pill so that women can make fully informed choices about contraception" (Guardian, 4/4). The researchers said that it is very important for all women to be screened for cervical cancer regardless of whether they take oral contraceptives (BBC News, 4/4).