p53 protein expression in transitional mucosa and adenocarcinomas of the colorectum.

Transitional mucosa, the nonneoplastic mucosa adjacent to colorectal adenocarcinomas, exhibits some morphologic and histochemical abnormalities. It is unclear, however, whether transitional mucosa is a preneoplastic or reactive phenomenon. Though normal p53 functions as a tumor suppressor, p53 gene alterations have been proposed as a step in malignant transformation, and aberrant p53 protein expression has been described in a high percentage of colonic adenocarcinomas. Since p53 protein normally has a short half-life, immunohistochemical detection of the protein is considered to be evidence of abnormal p53 expression. We analyzed p53 protein expression immunohistochemically on frozen tissue samples of transitional mucosa, normal mucosa, and tumor from 20 cases. In all 20 cases the transitional mucosa and normal mucosa failed to express p53, while 13 of 20 adenocarcinomas showed positive immunoreactivity characterized by intense nuclear staining. There was no correlation between tumor stage and p53 expression. The absence of staining for p53 protein in TM does not support the theory that transitional mucosa is a preneoplastic phenomenon.