Bcl-2 expression in colorectal tumours. Correlation with p53, mdm-2, Rb proteins and proliferation indices

Immunostaining for bcl-2 protein was performed in 27 colorectal adenomas an d 108 colorectal adenocarcinomas. The aim of the study was to determine bcl -2 expression in correlation with p53, mdm-2 and Rb expression, with prolif eration indices (Ki-67-LI, PCNA-LI) as well as with conventional clinicopat hological variables. A higher proportion of adenomas (30.8%) than carcinoma s (16.7%) expressed bcl-2 and conversely, a lower proportion of adenomas (7 .4%) than carcinomas expressed p53 (57.1%), the difference being statistica lly significant (p<0.0001). No correlation of bcl-2 expression with p53 exp ression (parallel or inverse) as well as with the other parameters studied was observed in any tumour. The bcl-2(+)/p53(-) subgroup of cancers showed a trend for correlation with negative lymph node status. Our data suggest, that bcl-2 expression may be involved in the early phase of colorectal carc inogenesis regardless of p53 status, while p53 function may be involved in a late stage of the adenoma-carcinoma sequence. P53 is apparently not invol ved in the regulation of apoptosis in the colorectal neoplasias or perhaps bcl-2 expression, as an early event in colorectal tumours, may occur before changes of p53 take place. Tumours with bcl-2(+)/p53(-) immunophenotype ar e frequently associated with negative lymph node status and seem to have a less aggressive behavior.