Women who take the birth control pill for 10 years have nearly double the normal risk of developing cervical cancer, but the risk begins falling as soon as they stop and returns to near normal within 10 years, according to a study released Thursday.
The study confirms previous research linking the pill with an increased risk of cervical cancer and reveals for the first time that the risk falls after pill use stops, said Dr. Jane Green, a University of Oxford clinical epidemiologist who led the study, which was reported in the medical journal Lancet.
Green said that the pill's increased risk of cervical cancer -- like its increased risk of breast cancer, revealed in previous studies -- is small and is "outweighed by reduced risks for ovarian and womb cancer."
The results should "reassure women that fear of cervical cancer should not be a reason not to take oral contraception," wrote Dr. Peter Sasieni, a professor at the Queen Mary University of London, in an editorial accompanying the report.
Researchers were interested in how long the increased risk persisted, because the incidence of cervical cancer peaks in women's 30s, several years after many have stopped using the pill.
Green and her colleagues from the International Collaboration of Epidemiological Studies of Cervical Cancer combined results from 24 studies involving more than 52,000 women in 26 countries.
In industrialized countries, they concluded, the overall rate of cervical cancer among women who have never taken the pill is 3.8 cases per 1,000 women. The rate rises to 4.0 per 1,000 in women who took the pill for five years and 4.5 for those who took it for 10 years.
For women who are well-screened, Sasieni said, that translates into an additional two cases per 10,000 women. In less-developed countries where screening is not as prevalent, however, that translates to an increased risk of about 40 cases per 10,000, he said.
The hormones contained in the pill are only a secondary cause of cervical cancer, Green and Sasieni emphasized. The disease's primary cause is the human papillomavirus. Researchers are not sure how the pill's hormones increase risk, but they may work by making cervical cancer cells more susceptible to infection or by accelerating the cancer's progression once an infection occurs.
Increased use of HPV vaccines should significantly reduce the incidence of the disease, said Dr. Lesley Walker, director of Cancer Research UK, which sponsored the study along with the World Health Organization and the International Agency for Research on Cancer.