Anal cancer shares many similarities with cervical cancer and it has therefore been proposed that cervical HPV management paradigms might successfully be applied to people at high risk of anal squamous cell cancer (ASCC). However, early evidence suggests that approaches developed for the cervix may need to be modified for the anus.
The Study for the Prevention of ANal Cancer (SPANC) set out to gain an understanding of the natural history of anal HPV infection and associated conditions. This could then provide an evidence basis for the development of interventions designed to reduce the clinical burden of ASCC.
From 2010, a total of 617 gay and bisexual men were enrolled into a study requiring five visits over three years. At each visit, participants had an anal swab tested for cytological changes and HPV detection using the Linear Array method. High Resolution Anoscopy was performed at each visit and biopsies taken from any areas suspicious of High grade Squamous Intraepithelial Lesions (HSIL). Unlike most other studies, participants were not routinely treated for any detected clinical abnormalities.
86.7% of participants had ≥1 anal HPV type detected and 29.4% had HPV16. Over one third of participants (35.3%) had no nonovalent prophylactic HPV vaccine (9vHPV)-preventable HPV types detected. HPV16 was the most common prevalent HPV type (29.4%). The incidence of anal HPV16 infection was 3.64 per 100 per year. The incidence of infection with one or more 9vHPV targeted genotypes was 17.78 per 100 per year. There was no difference in incidence of HPV16 or other 9vHPV type by age or HIV status. At baseline, 36.7% had cytological and/or histological HSIL. The number of lifetime receptive anal partners, HIV status and HPV16 were all associated with the detection of HSIL-AIN3.
HPV16 was more likely to persist at six months, compared to other high risk HPV (HRHPV) genotypes. In men with HSIL at baseline, 22% cleared their HSIL at one year. Clearance of HSIL was associated with younger age, but not HIV status. Persistence of HSIL was strongly associated with the detection of any high risk HPV and HPV16 at baseline and persistent infection with these genotypes. Persistence of HSIL was more likely to occur in those with larger lesions.
The high percentage of individuals with prevalent anal high risk HPV and HSIL, together with the transient nature in some participants, suggests that further risk stratification techniques might be helpful in identifying those at highest risk of developing ASCC. Monitoring and treatment resources could then be more specifically targeted at such individuals, reducing unnecessary investigation and treatment.