Incidence and epidemiology of anal cancer in the multicenter AIDS cohort study

Abstract

Objective: To examine the incidence and risk factors for anal cancer in a multicenter cohort of human immunodeficiency virus (HIV) positive and HIV-negative men who have sex with men followed between 1984 and 2006 (Multicenter AIDS Cohort Study).

Methods: Prospective analysis using Poisson regression and Cox proportional hazard models and a nested case-control study using conditional logistic regression.

Results: There were 28 cases of anal cancer among the 6,972 men who were evaluated. The incidence rate was significantly higher in HIV-positive men than in HIV-negative men (incidence rate = 69 vs 14 per 100,000 person-years). Among HIV-positive men, anal cancer incidence was higher in the highly active antiretroviral therapy (HAART) era than the pre-HAART era (incidence rate = 137 vs 30 per 100,000 person-years). In multivariate analysis restricted to the HAART era, anal cancer risk increased significantly with HIV infection (relative hazard = 4.7, 95% confidence interval = 1.3 to 17) and increasing number of unprotected receptive anal sex partners at the first 3 study visits (P trend = 0.03). Among HIV-positive men, current HAART use did not decrease anal cancer risk.

Conclusions: HIV-positive men had increased risk of anal cancer. Improved survival of HIV-positive individuals after HAART initiation may allow for sufficient time for human papillomavirus-associated anal dysplasias to develop into malignancies, thus explaining the increased incidence of anal cancer in the HAART era.

Figure 1

Comparison of the number of unprotected receptive anal sexual partners reported at the first three semi-annual study visits in those men in the study who later developed anal cancer compared to all other study participants. Median (white line), 25% and 75% (upper and lower bounds of box), 95% confidence limits (bracketed lines), and outliers are displayed above.

Figure 2

Kaplan-Meier probability curve of time free of anal cancer in HIV-positive (HIV+) men in the pre-HAART(1984–1995) and HAART (1996–2006) eras compared to HIV-negative (HIV-) men. Age is used as the time axis. Staggered entry is used to assume time of origin back to age 30 for all participants. This includes men enrolled in each of the three study enrollment calendar periods (1984–85, 1987–91, and 2001–03).