NCIt definition : A precancerous neoplastic intraepithelial process involving the anal canal. When it
is clinically noticeable, it may appear as an eczematous or papillary lesion, plaques,
or papules. Morphologically, it is characterized by loss of epithelial stratification
and nuclear polarity, cytologic atypia, and the presence of mitotic figures. It may
be classified as low or high grade.;