AN IMMUNOHISTOCHEMICAL STUDY OF THE SIMULTANEOUS EXPRESSION OF BCL-2 AND P53 ONCOPROTEINS IN EPITHELIAL TUMORS OF THE COLON AND RECTUM

Objective.--Bcl-2 and p53 genes may participate in a common pathway fo r regulation of apoptosis. The aims of this study were (1) to study th e immunohistochemical expression of the bcl-2 oncoprotein in colorecta l 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 expressio n of bcl-2 and p53 oncogenes in colorectal tumors. We examined 6 color ectal hyperplastic polyps, 33 adenomas, and 61 carcinomas. Setting.--R egional academic medical center. Methods.-An immunohistochemical study with bcl-2 and p53 antibodies was performed on frozen sections of col orectal tumors. The levels of bcl-2 and p53 expression were evaluated using a semiquantitative grading system. Two-color immunohistochemistr y was performed to examine the intracellular colocalization of bcl-2 a nd p53 in all tumors with a strong positivity for both antigens. Resul ts.--Bcl-2 was expressed in 28 (85%) of the 33 adenomas, whereas p53 w as 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 on coproteins. There was no correlation between the number of cells expre ssing bcl-2 and the number expressing p53 in a given carcinoma. No cor relation was observed between the expression of bcl-2 or p53 and the e stablished prognostic factor. Conclusion.--Abnormal bcl-2 oncoprotein expression appears earlier than p53 accumulation in colorectal carcino genesis. This study suggests that there is more than one sequence and mechanism of bcl-2 and p53 gene deregulation in colorectal carcinomas.