An overview of anal intraepithelial neoplasia.

Anal intraepithelial neoplasia (AIN) and anal squamous cell carcinoma (ASCC) are on the rise in the United States, especially among men who have sex with men, HIV-positive or other immunocompromised patients, and women with a history of cervical, vaginal, or vulvar cancer. Strong evidence supports the human papillomavirus as the causative factor in anal dysplasia; reducing the risk of HPV infection can reduce rates of ASCC. High-risk patients should be screened for AIN, but no universal screening guidelines exist, and more studies are needed to develop a national protocol for screening and management of patients with AIN.