Malignant progression of anal intra-epithelial neoplasia.

Background: Anal intra-epithelial neoplasia (AIN) is believed to be a precursor to squamous cell carcinoma of the anus. The risk of developing anal cancer in patients with AIN, although known to occur, has been thought to be relatively low. This study reviews our experience with AIN, reviewing the incidence and risk factors for development of invasive malignancy and the outcome of present management strategies.

Methods: This study examined a cohort of 72 patients identified from a prospective database with AIN from a single institution between January 1996 and December 2004. A single pathologist examined all pathological specimens.

Results: There were 72 patients (52 women) and the median age was 49 years (range, 18-81 years). We identified progression of AIN to invasive malignancy in eight patients despite undergoing surveillance. Regression following treatment or biopsy was seen in 25 patients. Four patients required stomas for incontinence following treatment.

Conclusion: This study has shown a high rate of progression to invasive malignancy (11%) with AIN despite surveillance. The patients at risk of developing squamous cell carcinoma were the immunocompromised and those with genital intra-epithelial field change. Treatment of AIN has significant complications and despite treatment, invasive cancers do occur. Decisions made for treatment of AIN can affect treatment choices if invasive malignancy develops.