Squamous differentiation in colorectal adenomas. Literature review, histogenesis, and clinical significance.

Patterns of stratified squamous epithelium have been recognized recently in colorectal adenomas. Light microscopic and keratin immunohistochemical analysis of four cases in the present report suggested origin from large intestinal reserve cells, with impaired and disorderly maturation in the squamous foci. One case had an invasive adenocarcinoma separately in the same polyp, bringing the reported incidence of malignant transformation in these adenomas to seven of 48 (15 percent). Evidence is presented to support the notion that squamous differentiation may be an inherently neoplastic phenomenon in colorectal adenomas, which may be added to the list of markers for colorectal polyps at higher risk for malignant transformation.