Background
People with HIV (PWH) have a higher anal cancer incidence than the general population. Although most PWH live in sub-Saharan Africa, data about the association of HIV and anal cancer in this region are scarce. We examined anal cancer incidence rates among privately insured people with and without HIV in South Africa.
Methods
We did a retrospective cohort study using reimbursement claims data from a South African medical insurance scheme (01/2011-07/2020) to assess anal cancer rates among people with and without HIV aged ≥18 years. We defined anal cancer diagnoses as ≥2 claims with ICD-10 codes for anal cancer (C21). Using proportional hazards survival models, we estimated adjusted hazard ratios (aHRs) for the association of HIV and incident anal cancer. The multivariable model included sex, HIV status, age, population group, calendar year, history of genital warts, and history of other sexually transmitted infections (STIs). Among women, we also estimated aHRs for the association of past cervical precancer and an incident anal cancer diagnosis.
Results
We included 1,068,915 people of whom 557,717 were women (52%) and 69,985 (7%) were PWH. The median age at the start of time-at-risk was 39.7 years (interquartile range [IQR] 33.4-47.3) in PWH and 36.3 years (IQR 26.1-49.9) in people without HIV. Over 3,933,145 person-years, 122 incident anal cancers were diagnosed for a crude incidence rate of 3.1/100,000 person-years (95% confidence intervals [CI] 2.6-3.7). PWH had a four-fold higher risk of an incident anal cancer diagnosis than people without HIV (Table). Anal cancer rates increased with older age, and they did not differ by sex. A history of genital warts was associated with a substantially higher risk of an incident anal cancer diagnosis, but we did not find a clear association with a history of other STIs. Among women, a prior diagnosis of cervical precancer was associated with an almost six-fold increased risk of developing anal cancer (aHR 5.70; 95% CI 1.75-18.58).
Conclusions
We found that PWH in South Africa had considerably higher anal cancer rates than people without HIV. Older individuals, people with a history of genital warts, and women with a prior diagnosis of cervical precancer were also at increased risk of developing anal cancer – these groups may benefit from risk-targeted anal cancer screening, as recommended by the International Anal Neoplasia Society’s consensus guidelines for anal cancer screening.
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