Prolonged use of oral contraceptives (OCs) is associated with an increased risk of cervical cancer, a new analysis has confirmed. The relative risk in women who had taken OCs for five years and over was almost double that of non-users, the researchers found.

However, this effect was also reversible. Once women came off the pill, the risk of cervical cancer declined and after 10 or more years it had returned to the same level as in women who had never taken oral contraceptives. Given that the incidence of cervical cancer rises with age, and taking into account the reduced risk of ovarian and endometrial cancers seen with OCs, the study outcomes are not a reason for younger women to stop taking the pill, the authors suggested.

Researchers from the International Collaboration of Epidemiological Studies of Cervical Cancer, led by Dr Jane Green from the Cancer Epidemiology Unit at the University of Oxford, UK, analysed data from 24 epidemiological studies involving, respectively, 16,573 and 35,509 women with and without cervical cancer. The results were published in the latest edition of The Lancet (2007; 370:1609-1621).

Among current users of oral contraceptives, the data revealed, the risk of invasive cervical cancer rose with increasing duration of use. In women who had taken the pill for five years or more, the relative risk of cervical cancer compared with women who had never taken the pill was 1.90 (95%, confidence interval 1.69-2.13). Using OCs for 10 years between the ages of around 20 and 30 years was estimated to increase the cumulative incidence of invasive cervical cancer by age 50 from 7.3 to 8.3 per 1,000 in less developed countries and from 3.8 to 4.5 per 1,000 in more developed countries.

Once women came off the pill, the risk of cervical cancer started to fall and after 10 or more years it was comparable to that of women who had never taken OCs, the analysis showed. A similar pattern of risk was seen for both invasive and in situ cervical cancer, as well as in women testing positive for high-risk human papillomavirus (the sexually transmitted virus that causes cervical cancer).

In the long term, Dr Green commented, the small increases in the risk of cervical and breast cancer observed with OC use are outweighed by the reduced risk of ovarian and endometrial cancer.

The study results came shortly after data from a Belgian study, presented at the annual meeting of the American Heart Association, suggested that taking oral contraceptives could increase the risk of atherosclerosis by 20-30% for every 10 years of use.