Figure 6.

Models of morphogenesis of sporadic adenomatous polyps. (A) Transformation of a single epithelial cell occurs at the base of the crypt (arrow) by virtue of APC inactivation. The transformed cell proliferates and passively migrates upward as a result of routine epithelial turnover. Once the transformed cells reach the superficial portion of the mucosae, they continue to proliferate and migrate and begin to populate the superficial mucosae of the adjacent crypts. The adenomatous epithelium thereby confronts the normal epithelium of the adjacent crypts, pushing the latter downward and gradually replacing it from top-to-bottom. (B) Similar to A except that the initial transformation event occurs in an epithelial cell in the intercryptal zone lying between crypt orifices (arrow). (C) En face view of surface, indicating spread of intercryptal dysplastic epithelial cell to adjacent crypts.