Studies have provided conflicting data for calendar trends in anal cancer among HIV+ individuals, one of the most frequent cancers in this population. Our objective here was to compare the risk of anal cancer between HIV+ and HIV- individuals in North America, and how this relationship has changed over time.

We conducted a cohort study involving 12 cohorts from North America followed between 1996 and 2007. Anal cancer incidence rates were compared between HIV+ men who have sex with men (MSM), HIV+ non-MSM (including women), and HIV- individuals. We calculated rate ratios (RRs) using multivariable Poisson regression with adjustment for age, sex, race/ethnicity (26% imputed), and calendar era. We next determined whether the adjusted RR for HIV+ compared with HIV- controls has changed over time. Since only a subset of cohorts contributed HIV- controls, we also computed age- and sex- and race-standardized incidence ratios (SIR) using national U.S. SEER rates.

Cohort-specific HIV+ anal cancer incidence rates ranged across cohorts from 0 to 154 cases per 100,000 person-years. The cohort-specific prevalence of MSM explained 58% of the total variability in rates. Overall, there were 111 anal cancer diagnoses among 15,907 HIV+ MSM, 38 diagnoses among 18,239 HIV+ non-MSM, and 79 diagnoses among 115,469 HIV- individuals. The corresponding adjusted RRs were 66.6 (95% CI: 36.9-120.2) for HIV+ MSM and 23.4 (95% CI: 11.9-46.1) for HIV+ non-MSM compared with the HIV- control group. For both HIV+ MSM and non-MSM, the RR was highest in 1999-2002, but the RR decreased for both groups in the most recent calendar era, 2003-2007 (Table 1), although the differences were not statistically significant (p>0.2) comparing RRs across eras. Inferences were similar for SIRs.

Despite an aging HIV+ population with presumed longer exposure to the oncogenic effects of human papillomavirus, the relative incidence of anal cancer among HIV+ individuals in the most recent calendar era has not increased. It is possible that improvements in immune function resulting from effective antiretroviral therapy contributed to this result.