The precursor tissue of ordinary large bowel cancer.

Hyperplastic polyps are 10 times as common as adenomas and must be distinguished from them since they are unrelated as a precursor tissue to either adenomas or carcinomas. Only adenomas are relevant to the development of the common moderately and well-differentiated large bowel cancer. Depending on three related factors (increasing size, a sessile rather than pedunculated mode of growth, and a villous rather than tubular microscopic architecture), one may find minute (1 to 2-mm) or microcancer with increasing frequency in adenomas. However, despite unlimited opportunity to do so, minute or microcancer has not been observed in normal mucosa, i.e., unassociated with adenomatous tissue. The same findings obtain in familial polyposis. In this condition, in grossly normal areas of mucosa, adenomas (but not carcinomas) as small as one or two crypts have been found. Direct one-step transformation from normal crypt cells to cancer, without formation of adenomatous epithelium, does not seem to be the usual pathway.