Anal infection with HPV-16, the type of human papillomavirus most strongly associated with anal cancer, is most common in HIV-positive gay men, similar between HIV-negative gay men and HIV-positive heterosexual men, and lowest among HIV-negative heterosexual men, according to a meta-analysis of studies of HPV-16 prevalence in men published in Clinical Infectious Diseases.
Anal cancer is relatively rare, affecting approximately 35,000 people each year worldwide. But previous studies have provided some evidence that anal cancer is more common in men who have sex with men (MSM) and especially in those who are HIV positive.
A previous meta-analysis of 95 published studies by the same research group showed that HPV-16 is the HPV type most strongly associated with anal cancer. The newly published analysis investigated in more detail show differences in the risk of anal HPV infection in men, according to HIV status and sexual orientation.
Systematic review identified 79 studies which reported on the prevalence of anal HPV-16 and other potentially carcinogenic HPV types in men, stratified by sexual orientation and HIV status. The studies included 23,700 people, of whom 12,215 participants in 43 studies had undergone anal examination in addition to HPV DNA testing.
In those who underwent an anal cytopathology examination, 5737 had normal anal cytology, 4907 had a low-grade abnormality, 1548 had a high-grade abnormality and 23 were diagnosed with anal cancer. (High-grade abnormalities in anal cells may lead to the development of anal cancer.)
Meta-analysis showed that anal HPV-16 prevalence was highest among HIV-positive MSM (30%), similar between HIV-negative MSM and HIV-positive men who have sex with women (MSW) (14% and 11% respectively) and lowest among HIV-negative MSW (3%). Any type of anal HPV was detected in 81% of HIV-positive MSM, 47% of HIV-negative MSM, 44% of HIV-positive MSW and 12% of HIV-negative MSW.
Low-grade and high-grade diagnoses were more common in HIV-positive MSM than HIV-negative MSM (59% vs 42%, p < 0.0001) but there was no difference in the prevalence of anal cytology abnormalities by HIV status in MSW (who comprised 11.5% of the entire population and 7.5% of those who received anal cytology examination).
Compared to MSW, the prevalence of HPV-16 was almost five times higher in HIV-negative MSM (prevalence ratio 4.8, 95% CI 3.8-6.1) and twice as high in HIV-positive MSM (prevalence ratio 2.0, 95% CI 2.5-8.9).
When compared to HIV-negative men, HIV-positive MSW had a higher prevalence of HPV-16 (PR 3.5, 95% CI 2.4-5.2), as did HIV-positive MSM (PR 1.5, 95% CI 1.3-1.6).
HPV-16 prevalence was highest among men with diagnoses of high-grade anal abnormalities (43-49%) with no significant difference according to HIV status or sexual orientation.
The meta-analysis also showed that even in men with normal anal cytology, the prevalence of HPV-16 was much higher in MSM, especially in HIV-positive MSM (22%, compared to 13% in HIV-negative MSM and 7% in HIV-positive MSW).
The study authors say that HIV-positive MSM “clearly stand out from other male sub-populations in terms of their anal HPV-16 prevalence, and are hence priorities for male anal cancer prevention.”
But they also warn that the high prevalence of HPV-16 in the MSM populations studied means that recommendations to vaccinate MSM under the age of 45 (or 27 years in some countries) may have limited effectiveness. They draw attention to international and national guidelines which recommend either regular digital rectal exams or anoscopy for HIV-positive MSM as secondary prevention measures for anal cancer.