Anal cancer is more common in MSM and even more common if they have HIV. Anal intra-epithelial neoplasia (AIN) appears to be the precursor and considerable effort is being directed toward evaluating the effectiveness of screening for and treating AIN to prevent anal cancer. This is analogous to the cervical screening programs in wealthy countries. But AIN screening and treatment differs from cervical screening and treatment in several key ways that may delay its introduction into routine clinical care.
First we do not fully understand the natural history of AIN, and particularly why AIN is so prevalent (20 to 50% of HIV+ MSM) when anal cancer is relatively rare. Second, the process of screening for AIN is troubled by problems with non-specific cytology and a resulting high demand for uncomfortable high-resolution anoscopy. Third, there is no consensus on the ideal treatment for AIN; most treatments involve high rates of recurrence, complications, or both.
While we await resolution of these uncertainties, some guidelines recommend regular digital rectal examination (DRE) for early detection of anal cancer. Anal cancers smaller than 3cm when they are treated, have significantly lower recurrence rates and higher five-year survival, suggesting that regular digital examinations will be beneficial. Interim data from a retrospective analysis of anal tumour size will be presented. An ongoing study of routine DRE at Melbourne Sexual Health Centre suggests that the rate of referral for non-cancer diagnoses (false positives) is low and the examination is acceptable to MSM in the HIV clinic.
