Supplementary Material for: Follow-up time of anal cancer screening among women living with HIV at high risk of developing anal cancer

Introduction: Screening for anal cancer can help in its secondary prevention. We examined follow-up time for anal cancer screening among high-risk women living with HIV (WLHIV) and whether it varies with the number of risk factors for developing anal cancer.

Methods: A retrospective cohort study involving high-risk WLHIV under 65 enrolled in Medicaid for at least two years across 16 US states plus D.C. from 2009 to 2012. High risk was defined by a history of abnormal cervical test results or genital warts. Initial anal cancer screening was the first screening after a high-risk diagnosis, with results classified as normal or abnormal. Follow-up was until the next screening. Follow-up time was analyzed using the Kaplan-Meier estimator and the Cox Proportional Hazards model.

Results: Our cohort included 4,340 high-risk WLHIV, mean (±SD) age 41.8 (±10.2). About 18% (763/4,340) had both risk factors, while 9% (374/4,340) had abnormal results on their initial anal cancer screening. The median time, or the time at which 50% of the cohort received follow-up screening, was 17.53 (95% CI = 16.13, 18.30) months overall. Follow-up screening was more common in women with both risk factors for developing anal cancer compared to those with one risk factor [median time: 10.13 (95% CI = 8.90, 11.47) vs. 19.56 (95% CI = 18.36, 21.40) months; adjusted hazard ratio (aHR) = 1.53 (95% CI = 1.38, 1.68). The follow-up was also more common in women with abnormal results on the initial screening compared to those with a normal result [median time: 7.00 (95% CI = 5.40, 9.23) vs. 18.91 (95% CI = 17.92, 20.12) months; aHR = 2.00 (95% CI = 1.76, 2.28).

Conclusion: Follow-up time for anal cancer screening in high-risk WLHIV was about 1.5 years but varied according to the risk of developing anal cancer. Future research should examine the guideline-concordance of follow-up screening time given the recently issued guidelines for anal cancer screening.