Impact of screening and ART on anal cancer incidence in HIV-positive men who have sex with men: mathematical modeling study.

BACKGROUND: The incidence of anal cancer is high in HIV-positive men who have sex with men (MSM). We modeled the impact of screening strategies and combination antiretroviral therapy (cART) coverage on anal cancer incidence in Switzerland.

METHODS: Individual-based, dynamic simulation model parameterized with Swiss HIV Cohort Study (SHCS) and literature data. We assumed all men to be HPV infected. CD4 cell count trajectories were the main predictors of anal cancer. From 2016 we modeled cART coverage either as below 100% (corresponding to 2010-2015) or as 100%, and the following four screening strategies: (i) no screening, (ii) yearly anal cytology (Pap smears), (iii) yearly anoscopy and (iv) targeted anoscopy five years after CD4 count dropped below 200 cells/μl.

RESULTS: Median nadir CD4 cell count of 6,411 MSM increased from 229 cells/μl during 1980-89 to 394 cells/μl during 2010-15; cART coverage increased from 0% to 83.4%. Modeled anal cancer incidence peaked at 81.7/100,000 in 2009, plateaued 2010-2015 and decreased to 58.7 by 2030 with stable cART coverage, and to 52.0 with 100% cART coverage. With yearly cytology, incidence declined to 38.2/100,000 by 2030, with yearly anoscopy to 32.8 and with CD4 count guided anoscopy to 51.3. The numbers needed to screen over 15 years to prevent one anal cancer case (NNS) were 384 for yearly cytology, 313 for yearly anoscopy and 242 for CD4 count dependent screening.

CONCLUSIONS: Yearly screening of HIV-positive MSM may reduce anal cancer incidence substantially, with a NNS that is comparable to other screening interventions to prevent cancer.