Anal neoplasm Anal intraepithelial neoplasia 2019-01-15T10:14:28Z Risk factors for AIN and anal cancer consist of clinical factors and behaviors that are associated with the acquisition and persistence of human papilloma virus (HPV) infection. Anal cancer is defined as cancer arising from the squamous epithelium of the anus, making it distinct from colorectal cancer. The anal canal consists of stratified squamous epithelium originating outside the body and extending into the anus up to the dentate line, the point where it intersects the columnar epithelium of the rectum. Thus, the vast majority of anal cancer is squamous cell carcinoma (SCC), with a small minority consisting of adenocarcinoma or skin cancer variants. Anal cancer is preceded by intraepithelial neoplasia, a premalignant lesion. Anal intraepithelial neoplasia (AIN) is a premalignant lesion of the anal mucosa that is a precursor to anal cancer.