The researchers also report that smoking increases the risk of infection with specific types of HPV among both HIV-infected and uninfected older men by up to 20 percent. This is the first large U.S. study of a group of HIV-infected and uninfected men between the ages of 40 and 69 who have sex with men. Study participants were examined twice a year for up to 25 years.

"Invasive anal cancer is a health crisis for gay, bisexual and other men who have sex with men," said Dorothy J. Wiley, associate professor at the UCLA School of Nursing and lead author of the study, which was published Nov. 20 in the journal PLOS ONE. "Right now, invasive anal cancer rates among HIV-infected men who have sex with men surpass rates for seven of the top 10 cancers in men."

The study, which involved more than 1,200 participants, was performed at four sites in the United States. Nearly 49 percent of the men were HIV-positive. During semi-annual visits, all the men were examined for demographic, sexual, behavioral and HIV-infection characteristics and were tested for HPV.

The researchers found that HPV infections were common among all the men in the study and that the proportion of men affected by HPV remained consistently high across the 40-69 age range. However, HIV-infected men between the ages of 40 and 69 showed a higher risk for HPV infection than HIV-uninfected men.

The study also found that for HIV-positive men, taking antiretroviral therapies as prescribed appeared to lower their risk for the HPV infections that cause cancers. Avoiding tobacco use also lowered the risk of HPV infections among all the men.

"This study highlights the benefit of adhering to HIV treatment, which among HIV-infected men who have sex with men, is important for cancer-prevention strategies," Wiley said.

The next step in this research is to begin looking at ways to develop better, more effective HPV infection-prevention strategies, including vaccination for age-eligible males and screening and treatment programs for high-risk men who have sex with men to prevent invasive cancers.

"Right now, we perform colonoscopies to prevent colon cancer, where 53 men per 100,000 are diagnosed annually," Wiley said. "Unfortunately, we do not provide screening tests routinely for anal cancer for men who have sex with en, where the numbers are much higher -- 78 men per 100,000."