Increased risk of anal cancer for all groups with HIV

Gay men are not the only group of HIV-positive patients who have an increased risk of anal cancer, according to North American research published in the online edition of Clinical Infectious Diseases. The researchers found that incidence of the cancer was also significantly higher in non-gay HIV-positive men as well as HIV-positive women when compared to individuals in the general population.

“We confirmed that HIV-infected MSM [men who have sex with men] experienced the greatest risk of anal cancer,” write the authors. “We also found that both HIV-infected other men and women had substantially higher rates than HIV-uninfected men and women, and that HIV-infected other men and women had similar rates.” They believe that their findings may have implications for anal cancer screening strategies.

Thanks to improvements in HIV treatment and care the prognosis of many HIV-positive patients is now near normal. However, HIV-positive patients appear more likely to develop certain malignancies, including anal cancer, compared to their HIV-negative peers.

Understanding the incidence of anal cancer in the different populations affected by HIV can help develop strategies to prevent the cancer.

Therefore investigators from the North American AIDS Cohort Collaboration on Research and Design (NA-ACCORD) analysed findings from 13 US and Canadian studies. Their aims was to determine incidence of anal cancer in HIV-positive patients, who were divided into three categories – MSM, other men and women.

Rates of anal cancer in these HIV-positive patients were compared to those observed in HIV-negative men and women. Analyses were also conducted to see if there were temporal trends in anal cancer incidence, and if any specific risk factors for the malignancy in HIV-positive patients could be identified.

A total of 34,000 HIV-positive patients (55% MSM, 19% other men, 26% women) and 110,000 HIV-negative controls (90% men) were included in the study.

Data gathered between 1996 (the year effective HIV therapy first became available) and 2007 were examined by the investigators.

Incidence of anal cancer in MSM was 131 per 100,000 patient years. Among HIV-positive other men incidence of the malignancy was 46 per 100,000 years, and incidence in HIV-positive women was 30 per 100,000 person years. Incidence was therefore significantly higher in HIV-positive MSM compared to other men (p < 0.01). However, incidence rates for HIV-positive other men and women did not differ significantly.

Over the same period, the incidence of anal cancer in HIV-negative men was just 2 per 100,000 person years. There were no cases of the malignancy in HIV-negative women.

The investigators calculated that the risk of anal cancer was 80-times higher for HIV-positive gay men compared to HIV-negative men (RR = 80.3; 95% CI, 42.7-151.1). HIV-positive other men were almost 27 times more likely to develop anal cancer compared to HIV-negative men (RR = 26.7; 95% CI, 11.5-61.7).

“Our finding of high anal cancer incidence rates in HIV-infected MSM, other men, and women suggests the need for enhanced primary and secondary prevention efforts among all HIV-infected persons, as opposed to a targeted approach,” write the authors

Incidence of anal cancer increased significantly in HIV-positive gay men between 1996-99 and 2000-2003 (p < 0.03). However, new cases of the malignancy then stabilised. A similar trend was observed in HIV-positive other men and women. The investigators suggest that the initial increase was a function of the improved prognosis of HIV-positive patients, which allowed long-term cell changes caused by high-risk strains of human papilloma virus to become cancerous. In contrast, the levelling of cancer rate was attributed to the beneficial effects of antiretroviral treatment on the immune system.

HIV-positive MSM were significantly more likely to develop anal cancer than other HIV-positive men (RR = 3.3; 95% CI, 1.8-6.0). The risk of the cancer was near identical for HIV-positive other men and women.

Other risk factors for the malignancy included older age (RR per additional ten years = 1.3; 95% CI, 1.1-1.5).

A higher baseline CD4 cell count was protective against the development of the cancer (RR CD4 cell count above 500 cells/mm³ vs. 200 cells/mm³ = 0.2; 95% CI, 0.1-0.3).

There is currently disagreement about the value of anal cancer screening for HIV-positive patients. However, the investigators suggest that this is likely to be cost effective. They note “the New York State AIDS Institute guidelines…recommend anal digital rectal examination for all patients, anal targeted anal cytology for MSM, for individuals with a history of anogenital warts, and for women with a history of abnormal cervical or vulvar histology.”

Silverberg MJ et al. Risk of anal cancer in HIV-infected and HIV-uninfected individuals in North America. Clin Infect Dis, online edition. DOI: 10.1093/cid/cir1012 (click here for the free abstract).