Purpose: Anal intraepithelial neoplasia (AIN) is the accepted precursor of anal squamous cell carcinoma (ASCC). There has long been a hypothesis that treating AIN may prevent ASCC. Many different treatment modalities have been suggested and studied. We conducted this systematic review to evaluate their efficacy and the evidence as to whether we can prevent ASCC by treating AIN.
Methods: MEDLINE and EMBASE were electronically searched using relevant search terms. All studies investigating the use of a single treatment for AIN that reported at least one end outcome such as partial or complete response to treatment, recurrence after treatment and/or ASCC diagnosis after treatment were included.
Results: Thirty studies were included in the systematic review investigating 10 treatment modalities: 5% imiquimod, 5-fluorouracil, cidofovir, trichloroacetic acid, electrocautery, surgical excision, infrared coagulation, radiofrequency ablation, photodynamic therapy and HPV vaccination. All treatment modalities demonstrated some initial regression of AIN after treatment; however, recurrence rates were high especially in HIV-positive patients. Many of the studies suffered from significant bias which prevented direct comparison.
Conclusions: Although the theory persists that by inducing the regression of AIN, we may be able to reduce the risk of ASCC, there was no clinical evidence within the literature advocating that treating AIN does prevent ASCC.
Keywords: AIN; Anal intraepithelial neoplasia; Anal squamous cell carcinoma; Cancer; HIV.