Infection With Multiple HPV Types Ups Cancer Risk

Women infected with more than one type of human papillomavirus (HPV) may be at particularly high risk of developing precancerous changes in the cervix, according to a new study.

More than 100 types of HPV exist, some of which cause genital warts. Certain HPV strains can cause high-grade lesions in the cervical tissue, which sometimes progresses to cancer.

Dr. Eduardo Franco of McGill University in Montreal and colleagues followed 2,462 Brazilian women ages 18-60 who underwent multiple HPV tests over four years. Rather than the HPV tests used in clinical practices, which essentially give a "yes/no" answer as to whether a woman has a high-risk type, the researchers used a more sophisticated test that specifically identified around 40 genital HPV types, including those considered high- and low-risk.

Two percent to 3 percent of women at any given test were infected with multiple HPV strains, the investigators found. Twenty-two percent of the women tested positive for different HPV strains at some point during the study period. Compared with women who tested HPV-negative during the first year of the study, those who were infected with one HPV strain were 41 times more likely to develop high-grade cervical lesions. For women who had been infected with two or three HPV types, the risk was 92 times greater. Those with four to six viral types were more than 400 times more likely to develop the lesions.

The researchers found the combination of HPV types 16 and 58 to be particularly risky. HPV-16 is one of four types targeted by the recently approved HPV vaccine Gardasil. Though the vaccine does not protect against HPV-58, Franco said Gardasil would likely take away the risk of co-infection with type 16.

It is not clear why infection with multiple HPV strains increased the odds of precancerous lesions, noted Franco. While it could be the direct effect of the viruses themselves, he said, it is also possible that multiple infections indicate a "faltering of the immune system" in some women, since the body is usually able to fight off HPV.

The study's results could affect cervical cancer screening and diagnosis, said Franco. Many experts argue that screening could be improved by routine use of genetic tests to identify cancer-related HPV types in cervical cell samples, in conjunction with standard Pap exams. By genetically analyzing HPV types, physicians could know if a woman was infected with more than one strain and in need of close monitoring to detect precancerous lesions early. "This is one more piece of evidence for why we would eventually need to test for HPV in the general population," as part of cervical cancer screening, said Franco.

The study, "Human Papillomavirus Infections with Multiple Types and Risk of Cervical Neoplasia," was published in Cancer Epidemiology Biomarkers & Prevention (2006;15:1274-1280).

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