Photo: Laboratory of Tumor Virus Biology/NIH

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Just over 20 percent of men with prostate cancer tested positive for the human papilloma viruses, or HPVs, an analysis published Monday in the journal Infectious Agents and Cancer found. The link suggests the viruses might be among the causes of a cancer that kills an estimated 30,000 American men each year, supporting the case for universal vaccination, the researchers said.

"The data may indicate that HPV infection may be transmitted during sexual activity and play causal role in prostate cancer, as well as cervical cancer [in women]," co-author James Lawson, a professor at the University of New South Wales in Australia, said in a statement. "Although HPVs are only one of many pathogens that have been identified in prostate cancer, they are the only infectious pathogen we can vaccinate against, which makes it important to assess the evidence of a possible causal role of HPVs in prostate cancer," he said.

Lawson and colleague Wendy Glenn at the University of New South Wales reviewed data from 26 previous studies on HPVs and their links to prostate cancer. The high-risk HPV types 16 and 18, which cause the majority of cervical cancers in women, have been identified in normal, benign, and malignant prostate tissues, they found. As many as 45 percent of American men 18 to 59 years old are positive for some form of genital HPV, according to the U.S. Centers for Disease Control and Prevention. These infections have been linked with cancers in the genital area in the past, the agency said.

The prevalence of high-risk HPV DNA, which indicates the presence of cancer-causing types, was significantly higher in prostate cancers compared to normal and benign prostate controls, according to Lawson and Glenn. Recent studies found that 231 of 1,071 prostate cancers -- or roughly 22 percent -- were HPV positive, whereas only 74 of 1,103 benign prostate controls -- just under 7 percent -- were HPV positive, they said. "We found reasonably consistent evidence that high-risk HPVs are significantly more prevalent in prostate cancers than in normal prostate tissues and benign prostate tissues," Glenn said.

How HPV infection potentially leads to prostate cancer in men is not clear and studies exposing normal prostate cells to HPVs are needed to investigate these mechanisms, the researchers said. It's possible that the viruses play an indirect role of in cancer formation by inhibiting the protective function of specific enzymes, they said. The viruses also might cause inflammation of the prostate, which can lead to benign prostate enlargement and later prostate cancer, they added. "HPVs are a common cause of cancers in men -- mainly genital cancers of the anus and penis, but also ... cancers of the mouth, tongue, and throat," Lawson said.

"It is therefore plausible that HPVs may also play a role in prostate cancer and that HPV vaccination may help prevent prostate cancer," Lawson said.