Objective: Bcl-2 and p53 genes may participate in a common pathway for regulation of apoptosis. The aims of this study were (1) to study the immunohistochemical expression of the bcl-2 oncoprotein in colorectal tumors, (2) to correlate it with that of p53 protein overexpression, and (3) to compare it with histopathologic prognostic factors, such as TNM classification and grade.
Design: Prospective study of expression of bcl-2 and p53 oncogenes in colorectal tumors. We examined 6 colorectal hyperplastic polyps, 33 adenomas, and 61 carcinomas.
Setting: Regional academic medical center.
Methods: An immunohistochemical study with bcl-2 and p53 antibodies was performed on frozen sections of colorectal tumors. The levels of bcl-2 and p53 expression were evaluated using a semiquantitative grading system. Two-color immunohistochemistry was performed to examine the intracellular colocalization of bcl-2 and p53 in all tumors with a strong positivity for both antigens.
Results: Bcl-2 was expressed in 28 (85%) of the 33 adenomas, whereas p53 was expressed in only one adenoma, which had areas of in situ carcinoma. Bcl-2 and p53 were each expressed in 43 (70.4%) of the 61 carcinomas. Thirty-one (50%) of the colorectal carcinomas coexpressed the two oncoproteins. There was no correlation between the number of cells expressing bcl-2 and the number expressing p53 in a given carcinoma. No correlation was observed between the expression of bcl-2 or p53 and the established prognostic factor.
Conclusion: Abnormal bcl-2 oncoprotein expression appears earlier than p53 accumulation in colorectal carcinogenesis. This study suggests that there is more than one sequence and mechanism of bcl-2 and p53 gene deregulation in colorectal carcinomas.