A CDC recommendation report issued by the Advisory Committee on Immunization Practices released late this summer calls for a better understanding of anal cancer development and screening among a population at high risk -- men who have sex with men (MSM). Although there's still uncertainty about the best way to screen for and treat anal cancer, here's what we know right now about who gets it, and what to look out for if you're worried.
Most often, anal cancer is caused by human papillomavirus (HPV), a sexually transmitted infection that takes up residence in the outermost layer of the skin or mucous membranes. This virus is stunningly common -- the most prevalent sexually transmitted infection in the U.S. Every year, 14 million new people get infected, with an estimated 79 million people infected in total. There are over 150 different kinds of HPV spread through skin to skin contact -- about 40 of which infect the genital tract. The ubiquity of HPV and ease of transmission means that people who end up getting HPV usually do so when they're young and with one of their first sexual partners.
Most of the time, HPV infection goes undetected and doesn't cause any health problems. Out of the 150 different types of the virus, only a few are known to cause clinical symptoms. Some strains of HPV, such as types 6 and 11, cause genital warts which can form in or around the genitals or anus. While likely to be a source of stress and discomfort, genital warts generally don't progress to cancer. They're considered by clinicians to be clinically benign -- while they may be annoying, they won't kill you.
Other strains of HPV can be dangerous. Two types of HPV, types 16 and 18, are known to cause cancer of the cervix, vulva, penis, and anus. People with HPV who go on to develop cancer first develop abnormal skin growths called high-grade squamous intraepithelial lesions (HSILs). These pre-cancerous growths, when left untreated, can go on to develop into cancer.
Men who have anal sex with men (MSM) are more likely to get anal HPV than men who only have sex with women. Researchers estimate that the prevalence of anal HPV among men who only have sex with women is around 15% while anal HPV prevalence for MSM is around 60%. If you add HIV into the mix, infection risk goes up still -- one study published by HIV Medicine found that 77% of MSM with HIV were also infected with anal HPV; another study published by the Journal of Infectious Diseases found that over 90% of MSM with HIV were infected with at least one strain of HPV.
This excerpt was cross-posted with the permission of BETAblog.org.