Women who reported using an intrauterine device (IUD) for contraception had almost half the risk of developing cervical cancer compared to those who had not, data from a large epidemiological study that involved more than 20,000 women indicate.

Although it is well known that IUDs reduce a woman’s risk of developing endometrial cancer, the devices’ affect on cervical cancer risk was unclear until now.

To better understand this relationship, Xavier Castellsagué, MD, of L’Hopitalet de Llobregat in Catalonia, Spain, and colleagues analyzed data from 10 cervical cancer case-control studies and 16 HPV prevalence surveys. The final pooled analysis included data from women with information available on IUD use, which encompassed 2,205 cases of cervical cancer and 2,483 matched case controls.

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The researchers found a strong inverse association between IUD use and cervical cancer, after adjusting for potential confounding factors including the number of previous Pap smears, number of sexual partners and age at first intercourse.

Women who had ever used an IUD had a 44% reduced likelihood of developing squamous cell carcinoma (P<0.0001) and a 54% reduced risk of developing adenocarcinoma or adenosquamous carcinoma (P=0.035) compared with those who had never used an IUD.

“Our data suggest that use of IUDs significantly reduces the risk of cervical cancer and that this effect does not seem to be due to differences in screening histories between users and nonusers,” the researchers wrote in Lancet Oncology.

This reduced risk occurred within the first year after initiating IUD use and did not increase or decrease depending on the duration of use, with protective effects remaining significant after 10 years.

Interestingly, no association was found between IUD use and the prevalence of HPV DNA in women without cervical cancer, suggesting that IUD use does not prevent HPV infections from occurring, but instead may mediate the progression of HPV to cervical cancer.

The researchers offered several hypotheses to explain the protective effects of IUDs, suggesting that device insertion and removal may destroy precancerous lesions, or that it may induce “a chronic mucosal inflammation and long-lasting immune response” that could halt progression.

In an accompanying editorial Karl Ulrich Petry, MD, of Klinikum Wolfsburg in Wolfsburg, Germany, wrote that the findings provide “a high level of evidence to contradict a widespread assumption that IUD use increases the risk of cervical cancer.”

“[These] surprising results should spark new research and might lead to revision of our current understanding of the genesis of cervical cancer,” he added.

Castellsagué X et al. Lancet Oncology. 2011;doi:10.1016/S1470-2045(11)70223-6.

Petry KU. Lancet Oncology. 2011;doi:10.1016/70255-8.