How HPV Infection Is Linked to Anal Cancer

Human papilloma virus (HPV), coloured transmission electron micrograph (TEM)
Science Photo Library - PASIEKA/Brand X Pictures/Getty Images

People often refer to HPV as the "cervical cancer virus." However, that's a misnomer. HPV is associated with a number of cancers in both women and men, including anal cancer. Anal cancer risk is associated with the practice of unprotected anal sex. That's in large part because of the potential for HPV infection during anal sex. The association between HIV and anal sex also increases anal cancer risk. Why? Because coinfection with both HIV and HPV increases the likelihood that a high-risk HPV infection will become cancerous.

How Common Is Anal Cancer?

Until recently, cervical cancer was thought to be the main cancer risk associated with HPV infection. Anal cancers and other genital cancers were thought to be relatively rare. However, although the overall anal cancer rate is still low, in certain populations the risk of anal cancer is actually quite high. For example, HIV-positive men who have sex with men (MSM), have been reported to have anal cancer rates that are very high. In fact, they're three times those of the highest cervical cancer rate seen in the general population.

It is hard to pin down the overall incidence of anal cancer since it varies strongly between countries and between populations. However, scientists estimate that there were 24,000 new cases of anal cancer reported in 2008. In addition, several other things are clear. Anal cancers are more common in women in the over 50 age group. However, when looking at younger populations, they're much more common in men. The other thing that's clear is that the incidence of these cancers is on the rise. Studies suggest that anal cancer rates have doubled over the past 20 years. It is estimated that approximately 88 percent of anal cancers are associated with HPV infection.

Risk Factors

Factors that increase a person's risk for developing anal cancer include:

  • having receptive anal sex
  • cigarette smoking
  • a high number of sexual partners
  • ever having been diagnosed with genital warts
  • HIV infection - particularly infections that have caused moderate to severe immunosuppression, even if several years in the past.

However, it's important to know that it is possible to end up with an anal HPV infection and even anal cancer even if you have never had receptive anal sex. The virus can migrate from other genital areas such as the vaginal canal or the perineum.

Will an Anal HPV Infection Definitely Lead to Cancer?

Just as has been seen with cervical HPV infections, only a small number of anal HPV infections progress and become cancerous. Most infections in heterosexual men and women clear within 6 months to a year. Infections tend to last longer in MSM for reasons that are not well understood. Therefore, even if you are diagnosed with an anal HPV infection, it is highly unlikely that you will develop cancer. That is true even if an anal pap smear detects abnormal cells. A large number of low-grade interepithelial neoplasias regress to normal and do not progress to become cancerous.

How to Reduce Your Risk

There are three very good ways to which people can reduce their risk of developing anal cancer. The first is to always practice safe sex. That's particularly true for anal sex, but also for any type of genital sex. Safe sex can't entirely eliminate the risk of HPV infections, which are passed from skin to skin. Still, it can significantly reduce the likelihood of infection.

The other major way to reduce your risk of anal cancer is to be vaccinated with an HPV vaccine. Ideally, individuals should be vaccinated as adolescents — long before they have become sexually active. However, the HPV vaccine may be worth considering even if you have had one or more sexual partners. You should discuss the cost/benefit ratio with your doctor, however, particularly if vaccination is not covered by insurance. Although the HPV vaccines are very safe, they are not cheap.

Finally, you can always reduce your chances of developing anal cancer, as well as a number of other cancers, by quitting smoking. Several studies have pointed to current cigarette smoking as a major risk factor in the development of anal cancer... and we all know that it's associated with other cancer risks as well.

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