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Because intrauterine devices (IUDs) pass through the cervix, concern has been raised that use of these highly effective reversible contraceptives might affect risk for cervical cancer. To explore the possible associations between IUD use, cervical cancer risk, and presence of cervical human papillomavirus (HPV) DNA, researchers pooled international data from 10 case-control studies of cervical cancer and 16 survey studies of HPV prevalence. Information on IUD use was obtained via interviews, and HPV status was determined with polymerase chain reaction–based assays. The case-control studies involved 2205 women with cervical cancer and 2214 matched controls without cervical cancer; an additional 15,272 healthy women participated in the HPV prevalence studies.
In meta-analyses adjusted for factors such as number of previous Pap smears, cervical HPV DNA status, and age at sexual debut, a protective association was found between ever use of an IUD and cervical cancer (odds ratio, 0.55; P<0.0001), whether squamous-cell carcinoma (OR, 0.56; P<0.0001) or combined adenocarcinoma and adenosquamous carcinoma (OR, 0.46; P=0.035). This benefit was not related to duration of IUD use. Among women without cervical cancer, IUD use was not associated with detection of cervical HPV DNA.
Castellsagué X et al. Intrauterine device use, cervical infection with human papillomavirus, and risk of cervical cancer: A pooled analysis of 26 epidemiological studies. Lancet Oncol 2011 Oct; 12:1023. (http://dx.doi.org/10.1016/S1470-2045(11)70223-6)
Comment
The mechanisms by which intrauterine device use might lower the rate at which human papillomavirus infection progresses to cervical cancer remain unclear. The authors hypothesize that IUDs might exert this protective effect by inducing a chronic, low-grade, sterile inflammatory response in the endocervical canal that could modify the course of HPV infection. Alternatively, preinvasive cervical lesions might be removed when the device is placed or removed. Although the authors controlled for many confounders, the possibility remains that screening bias led to residual confounding. Although types of IUDs were not specified in this analysis, in the countries where these studies were conducted, few women use hormone-releasing IUDs; thus, future work should be aimed at examining whether levonorgestrel-releasing IUDs prevent cervical cancer.