NCIt definition : A precancerous neoplastic intraepithelial process involving the squamous epithelium
of the perianal skin. Clinically, it usually presents as a white or red area in the
perianal skin. Morphologically, it is characterized by full thickness dysplasia of
the squamous epithelium and sometimes of the pilosebaceous epithelium. Human papillomavirus
DNA sometimes may be identified in the dysplastic epithelium. It may recur after treatment,
however only a small percentage of cases progress to squamous cell carcinoma.;