High prevalence, incidence and clearance of anal high-grade squamous intraepithelial lesions (HSIL) in homosexual men: early evidence from the Study of the Prevention of Anal Cancer (SPANC)
Homosexual men are at increased risk of anal cancer. Screening and treatment of the precursor, HSIL, has been advocated by some, but screening is not recommended in widely-accepted guidelines. We aimed to describe the prevalence, incidence, and clearance rates of anal HSIL, and association with human papillomavirus (HPV) status, in a community-recruited cohort of homosexual men.
Methods: The SPANC study is a three-year prospective study of the natural history of anal HPV infection and cancer precursors in HIV-negative and -positive homosexual men aged ≥ 35 years. At each visit all men undergo an anal swab for cytology and HPV genotyping (Roche Linear Array), followed by high resolution anoscopy-aided biopsy. Anal HSIL was defined as having either anal intraepithelial neoplasia grade 2/3 on histology and/or HSIL/possible HSIL on cytology.
Results: A total of 342 men were recruited by March 2013. Median age was 49 years (range: 35-79) and 28.7% were HIV-positive. At baseline, the prevalence of anal HSIL was 50.0% and 43.9% in the HIV-positive and HIV-negative respectively (p=0.303). Among those free of HSIL at baseline, HSIL incidence was 27.8 and 27.6 cases per 100 person-years in the HIV-positive and HIV-negative (p=0.920). Among those with HSIL at baseline, the clearance rate was 41.0 and 42.7 cases per 100 person-years in the HIV-positive and HIV-negative (p=0.851). Men who tested HPV16 positive on their anal swabs at baseline were significantly more likely to develop incident HSIL (57.1 vs 23.0 per 100 person-years, p=0.010), and less likely to clear prevalent HSIL (17.6 vs. 61.3 per 100 person-years, p=0.001).
Conclusion: Anal HSIL was highly prevalent in homosexual men. Both incidence and clearance of HSIL were common, and were closely associated with HPV16 status. The high rates of clearance are consistent with the observation that anal HSIL progresses to cancer less commonly than high-grade cervical lesions.
