AN international team of researchers has offered a possible explanation on the higher rates of anal cancer observed in gay men (men who have sex with men (MSM) compared to heterosexual men, (men who have sex with women MSW).In the study to be published in the December edition of the Journal of Infectious Diseases, researchers reported that anal human papillomavirus (HPV) infections were significantly more likely to persist in MSM than MSW.'Compared with MSM, we consistently observed a lower prevalence, incidence, and persistence of anal HPV among MSW,' they stated Human papillomavirus (HPV) was a common infection, which was transmitted sexually. Many sexually active people will be infected with HPV at some point in their lives and most people will have no symptoms.People often clear HPV infection without treatment.Some strains of HPV cause anal and genital warts, and certain strains (often those that don't cause visible warts) can cause cell changes that may lead to anal or cervical cancer. Rates of anal cancer are higher in gay men than heterosexual men and higher rates of anal cancer are seen in HIV-positive gay men.Rates of anal HPV infection alone do not appear sufficient to explain the different rates of anal cancer in gay men and heterosexual men. For example, one study showed that the rate of anal HPV infection was four times higher in gay men. However, rates of anal cancer were 36 times higher.An international team of researchers wanted to investigate whether it was the persistence of anal HPV infection that caused the increased risk of cancer.The research found that as well as overall rates of anal HPV infection being higher in gay men, anal HPV infection was indeed more likely to persist. Gay men were also more likely than heterosexual men to have new HPV infections during the study period, including those strains more likely to cause cancer.Smoking was also associated with the persistence of the anal HPV infection.Although rates of anal cancer are significantly higher in men who have sex with men, it is still a very rare cancer and there is a lot of debate about the value of screening gay men for pre-cancerous anal cell changes caused by HPV.Cigarette smoking was independently associated with the persistence of the infection in MSM.The investigators from Brazil, Mexico and the U.S. hypothesised that the explanation for the higher rates of anal cancer in MSM was the greater persistence of anal HPV infections in MSM compared to more transient infections in MSW.They designed a prospective observational study involving 156 MSM and 954 MSW. None were HIV-positive.The patients were screened for HPV infection at baseline and again after six months. Individuals were also asked to complete a questionnaire enquiring about their demographics, sexual behaviour, smoking habits and substance use.Baseline screening found a similar prevalence of anogenital warts in MSM and MSW (five vs. six per cent). However, MSM were significantly more likely to have anal infection with the cancer-associated HPV-16 strain (10 vs. three per cent).
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