Expression of p53 and bcl-2 in adenomas and colorectal carcinoma

Recent publications have associated p53 and bcl-2 genes in the process of neoplastic transformation. As the colonic adenoma-carcinoma sequence is an adequate natural model for carcinogenesis, it was considered interesting to analyze the expression of bcl-2 and p53 in these neoplasms. Seventy three adenomatous polyps (adenomas) and 60 adenocarcinomas of the colon and rectum were studied. Adenomas showed mild dysplasia in 16, moderate in 27, severe in 15 and focal carcinoma in the remaining 15. Adenocarcinomas surpassed the deep muscle layer in every case and were moderately differentiated. The studied gene expression was analyzed immunohistochemically using antibodies bcl-2 from Dako and p53 from Novocastra, both at a 1:100 dilution. Cytoplasmic stain for bcl-2 and nuclear stain for p53 above 10% of the cells were considered positive for each gene respectively. Results showed that there was accumulation of p53 protein in 26/58 (45%) adenomas with different grades of dysplasia. This result is similar to the reactivity found in adenomas with focal carcinoma where 8/15 (53%, p = 0.4) were positive but different from adenocarcinomas which were positive in 47/60 (78%, p = 0.0001). Regarding bcl-2, positivity was found in 53/73 (73%) of all the adenomas whereas adenocarcinoma showed expression in 14/60 (23%, p = 0.0000). When adenomas were grouped according to their degree of dysplasia and the existence of focal carcinoma, a diminishing frequency of reactivity for bcl-2 was found and when adenomas with three different grades of dysplasia were fused together, 47/58 (81%) were positive and this was compared with adenomas having focal carcinoma, 6/15 (40%) and with adenocarcinoma, 14/60 (23%), they showed significant differences (p = 0.001 and p = 0.0000 respectively). The analysis of the frequency of expression for both genes studied in the different lesions described yielded an inverse relation between them. This study allows the conclusion that the expression of bcl-2 is an early event in carcinogenesis and that it is replaced by nutation of p53 as the neoplastic change progresses.