Clinical evaluation of anal intraepithelial neoplasia: are we missing the boat?

Background: Anal intraepithelial neoplasia (AIN) is dysplasia in the epithelium of the anus and is a pre-malignant condition associated with a low rate of progression to invasive squamous cell carcinoma (SCC). The natural history of progression for AIN to anal SCC is poorly defined. This study aims to review our experience with AIN and investigate the natural history of progression.

Methods: Data on all patients with AIN from January 2005 to December 2015 were retrospectively reviewed. Three separate databases were searched - Colorectal, Radiation Oncology and Infectious Diseases. All databases were cross-referred to obtain a complete but non-duplicated data set. Electronic charts were reviewed to obtain clinical information.

Results: Twenty-eight patients were identified with AIN of various grades. There were 25 males, three females. Twenty of the male patients were human immunodeficiency virus (HIV) positive. Mean length of follow up was 56 months. Complete regression of AIN to normal was noted in 13 patients (46%). Four patients had persisting AIN III with no evidence of regression or malignant transformation. Nine patients with pre-existing AIN developed SCC (32%). Seven were positive for HIV infection (all males). Median time to progression was 36 months. None of the patients demonstrated clear linear pattern of progression of AIN to SCC.

Conclusion: High grade AIN may progress to anal SCC and surveillance is indicated. The exact natural history of progression for AIN is difficult to predict. There is no linear progression over time evident. HIV patients with AIN are at higher risk of developing SCC.