HIV infection has been major driver of anal cancer burden

Rising rates of anal cancer among men in the USA have been heavily influenced by the HIV epidemic since the 1980s, a study shows.

However, the authors found that while rates of anal cancer are higher in women than men, and have also increased during the same period, HIV infection has not significantly contributed to this.

Meredith Shiels (National Cancer Institute, Rockville, Maryland) and colleagues used data collected between 1980 and 2005 from the HIV/AIDS Cancer Match (HACM) Study, which incorporates 17 HIV/AIDS and cancer registries. During this time there were 20,533 anal cancer cases, of which 1665 (8.1%) occurred in HIV-infected patients.

Between 1980 and 1984 and 2001 and 2005, the incidence of anal cancer rose from 0.44 to 0.93 cases per 100,000 men and the proportion of anal cancers in HIV-positive men rose from 1.1% to 28.4%. Overall, 83.5% of HIV-infected anal cancer cases were in men who have sex with men.

Rates of anal cancer also increased in women. The authors estimated that between 1980 and 1984 and 2001 and 2005 the incidence of anal cancer rose from 0.68 to 1.29 per 100,000 years, and the proportion of anal cancer among HIV-positive women rose from 0% to 1.2%.

Shiels and colleagues found that while HIV-infected anal cancer cases strongly influenced the overall trend in incidence in men, exclusion of HIV-related cases had no effect on the increase in incidence rate in women.

While anal cancer is rare in the USA, it is the fourth most common cancer among HIV-infected individuals. The authors say that the association is likely to be related to anal human papillomavirus (HPV) infection, which is transmitted during anal sex. HIV-related immunosuppression may also impair the immune response to HPV infection, making HIV-infected individuals more susceptible to anal cancer.

They say that their findings could influence potential public health strategies such as HPV vaccination or Papanicolaou testing.

"Measures that would effectively prevent anal cancer in HIV-infected males could markedly reduce anal cancer rates at the population level," they write in the Journal of the National Cancer Institute. "In contrast, very few females with anal cancer were HIV-infected, and more research is needed to understand causes of rising anal cancer incidence in females."

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