The largest-ever study to determine whether a well-known cancer-causing virus is a risk factor for prostate cancer has found no connection between the two. According to new Public Health Sciences Division research, infection with human papillomavirus (HPV), which has been linked to genital and anal cancers, doesn't increase a man's changes of developing prostate cancer.
Although prostate cancer shares some risk factors with cervical, vaginal and anal cancers-tumors known to be strongly associated with prior infection with subtypes of the human papillomavirus (HPV)-researchers found no evidence for a link between viral strains known as HPV-16 and HPV-18 and prostate cancer.
The study should help put to rest questions first raised in 1990, said Dr. Janet Stanford, a PHS investigator and lead author.
"The observation that some aspects of sexual behavior-such as early age at first intercourse, higher numbers of lifetime sexual partners and a history of sexually- transmitted disease-have been linked to an elevated risk of prostate cancer focused attention on the possible role of infectious agents in prostate-cancer development," she said.
Stanford said that although several sexually-transmitted exposures have been examined in relation to prostate cancer, recent concern has centered on human papillomaviruses, some of which have been causally linked to anogenital tumors such as cervical and anal cancers.
"Several prior studies have reported a positive association between serological evidence of HPV infection and prostate cancer, but there were concerns about study methodology and limited study sizes," she said. "Our study is the largest conducted to date to assess the potential role of HPV-16 and HPV-18 in relation to risk of prostate cancer."
The results appear in the August issue of Cancer Epidemiology, Biomarkers and Prevention. Co-authors included Dr. Karin Rosenblatt at the University of Illinois at Urbana-Champaign; Dr. Joseph Carter, Human Biology; Lori Iwasaki, PHS; and Dr. Denise Galloway, PHS and Human Biology.
HPVs are sexually-transmitted viruses that are best known for causing genital warts. While all of the approximately 100 HPV subtypes can cause the growth of abnormal cells, usually only the high-risk variety-which include HPV-16 and HPV-18-are linked to cancer.
Plausible connections
Researchers tested serum samples from 642 King County men between the ages of 40 and 64 who had been diagnosed with prostate cancer for the presence of antibodies to HPV-16 and HPV-18. Antibodies are produced by immune-system cells upon exposure to infectious agents and persist in the blood serum for years after infection. For comparison, scientists also tested for the antibodies in blood serum from 570 men of similar age who did not have a history of prostate cancer.
Overall, researchers found no association between infection with either HPV-16 or HPV-18 and the risk of prostate cancer, although men who tested positive for antibodies to both viral subtypes had a slightly higher risk relative to men who tested negative for both subtypes.
"These results indicate that if there is an infectious agent that enhances risk of prostate cancer it is not likely to be HPV-16 or HPV-18," Stanford said. "However, it is possible that other as yet unrecognized viruses may play a role. It is also plausible that earlier associations with measures of sexual activity may be somewhat confounded by a man's hormonal milieu, which may differ among men with different sexual practices."
