p53 expression in colorectal adenomas.
To assess the expression of p53 in premalignant lesions, we examined by immunohistochemistry benign colorectal adenomas (n = 72, measuring more than 6 mm and less than 95 mm in diameter) from patients without (group I, n = 23) or with (group II, n = 49) concurrent sporadic colorectal carcinomas. Using a panel of three monoclonal antibodies (PAb 240, PAb 421, PAb 1801) and two polyclonal antibodies (CM1, C19) immunohistological staining was demonstrated in 26% of the cases (19 of 72 adenomas, 7 of 23 from group I and 12 of 49 from group II). In the majority of the cases, p53 positive foci in the adenomas occurred in the most dysplastic areas, although focal positivity was detected in glands that were histologically normal. Expression of p53 protein was also detected in 21 of 30 (70%) colorectal carcinomas of group II. In two cases focal positive staining was observed in the polyps but not in the concurrent carcinomas. Non-neoplastic colonic mucosa and stromal lymphoid cells were negative in all cases examined. Over-expression of p53 in neoplastic tissues detected by immunocytochemistry is generally believed to correlate with the presence of mutation in the gene. This may not be an absolute rule, because in some hemopoietic malignancies, there is evidence that p53 protein may be detectable in the absence of an underlying mutation. These findings therefore represent the highest incidence in colorectal adenomas of abnormalities in the p53 protein expression, probably largely due to underlying mutations. This study also suggests that immunocytochemical demonstration of p53 protein may be a suitable method for the routine detection of subpopulations of cells which, by clonal expansion, could acquire a growth advantage within an adenoma during the neoplastic process.