Impact of the HIV epidemic on the incidence rates of anal cancer in the United States

Abstract

Background: The risk of anal cancer is substantially increased in HIV-infected individuals. Thus, the HIV epidemic may have influenced the increasing anal cancer trends in the United States. We estimated the impact of the HIV epidemic on trends in anal cancer incidence in the United States during 1980-2005.

Methods: Data on anal cancer cases with and without AIDS were obtained from the HIV/AIDS Cancer Match Study. The number of HIV-infected anal cancer cases without AIDS was estimated from the number of anal cancers occurring before diagnosis of AIDS. The proportion of anal cancer cases with HIV infection in the general population was calculated. We estimated temporal trends in the incidence rates of anal cancer in the general population overall and after exclusion of HIV-infected cancer cases by calculating annual percent changes and 95% confidence intervals (CIs) using a Joinpoint log-linear model. All incidence rates were standardized to the 2000 US population by age, sex, and race.

Results: During 1980-2005, of the 20 533 estimated anal cancer cases, 1665 (8.1%) were HIV-infected. During 2001-2005, the proportion of anal cancer cases with HIV infection was the highest-1.2% (95% CI = 0.93 to 1.4%) among females and 28.4% (95% CI = 26.6 to 29.4%) among males. During 1980-2005, HIV infection did not have an impact on the trends in anal cancer among females (incidence rates increased by 3.3% [95% CI = 3.0 to 3.7%] annually overall, and by 3.3% [95% CI = 2.9 to 3.6%] annually without HIV-infected anal cancer cases) but had a strong impact on the trends in anal cancer among males (incidence rates increased by 3.4% [95% CI = 2.9 to 3.9%] annually overall, and by 1.7% [95% CI = 1.2 to 2.3%] annually without HIV infection).

Conclusion: During 1980-2005, the increasing anal cancer incidence rates in the United States were strongly influenced by the HIV epidemic in males but were independent of HIV infection in females.

Figures

Figure 1.

Anal cancer incidence in the general population with and without HIV-infected anal cancer cases, by age and sex, between 1980 and 2005. The solid lines represent the overall incidence rates of anal cancers in the general population; the dashed lines represent the incidence rates for anal cancers without HIV-infected anal cancer cases; the dark gray shaded areas represent anal cancer cases with AIDS, and the light gray shaded areas represent anal cancer cases with HIV-only. A) Incidence rates in males. B) Incidence rates in females. C) Incidence rates in males, stratified by age group. D) Incidence rates in females, stratified by age group.

Figure 2.

Anal cancer incidence in the general population in males and females by age group. Solid lines represent rates in females and dashed lines represent rates in males. A) Incidence rates in males and females overall. B) Incidence rates in males and females in the absence of HIV-infected anal cancer cases.