Background HPV vaccination of school-aged boys will prevent anal cancer in future generations. Vaccination of gay men up to age 26 is recommended in several jurisdictions, but vaccination is generally not recommended at older ages because of a concern of possible lack of efficacy due to past or current HPV infection. Anal cancer screening, based on the model of cervical cancer screening, has also been proposed as a means to reduce morbidity.
Methods The Study of the Prevention of Anal Cancer (SPANC) is a three-year prospective study of the natural history of anal HPV infection and cancer precursors in HIV-negative and -positive gay men aged ≥35 years. At each visit all men receive an anal swab for cytology and HPV genotyping, followed by high resolution anoscopy-directed biopsy for histological assessment.
Results At the end of June 2015, 595 men had been enrolled. Median age was 49 and 35.3% were HIV-positive. Men of all ages enrolled in SPANC were likely to report multiple sexual partners in the past 6 months (overall 73.4% of 35–44 year olds decreasing to 62.1% of 65+ year olds, p trend = 0.03). The prevalence of HPV16, the genotype responsible for >90% of anal cancer, was 29.4% in 35–44, 30.8% in 45–54, 34.2% in 55–64 and 19.0% in 65+ year olds (p trend = 0.54), with no difference by HIV status. The incidence of HPV16 decreased with age from 5.6/100 person years (PY) in 35–44 year olds to 2.9/100PY in 55–64 year olds. There was no incident HPV16 in men aged 65+ (p trend = 0.059). At baseline, the prevalence of anal high grade intraepithelial neoplasia (HSIL) was higher in HIV-positive than in the HIV-negative participants (46.9% vs 32.3%, p < 0.001). Among those with HSIL at baseline, the clearance rate was similar between HIV-positive and -negative participants (38.4 vs 38.0 per 100PY, p = 0.636).
Conclusions Gay men in SPANC reported multiple sexual partners across the adult age-range, and incident HPV16 continued to be detected in men up to their seventh decade of life. This suggests that HPV vaccination of adult gay men may prevent infection and have a role in cancer prevention. Anal HSIL is highly prevalent, particularly among HIV-positive men, but there are high rates of clearance without treatment. These data suggest that a screening test which can distinguish persistent from transient HSIL is required. The role of HPV biomarkers in identifying those HSIL lesions most likely to persist should be investigated.