Colon cancer: p53 expression and DNA ploidy. Their relation to proximal ordistal tumor site

Overexpression of nuclear p53 and DNA ploidy were analyzed in a series of 6 5 colorectal adenocarcinomas and correlated with standard clinical and path ological variables (Dukes stage, tumor site, histological grade and type, a nd nature of the tumor margins). Immunohistochemical tests were done with the DO-7 monoclonal antibody, usin g formalin-fixed tissue samples and an antigen retrieval solution. Levels o f p53 expression were evaluated using a semiquantitative grading system (CA S 200, BD). Nuclear staining of more than 15% of neoplastic cells was obser ved in 35 samples (53.8%), which were classified as p53-positive. DNA conte nt was measured by flow cytometry in samples of fresh tissue. Tumor site had a significant direct relationship with DNA ploidy (p < 0.01) and p53 expression (p < 0.001). Proximal tumors were more frequently diplo id than were distal tumors (78.6% vs 32%). Moreover, distal neoplasms showe d more p53 expression than proximal tumors (64.6% vs 14.3%). However, there was no correlation between the other clinical or pathological variables an d the pathological parameter p53 expression and DNA ploidy. Our data suppor t the hypothesis that mechanisms of colorectal carcinogenesis may differ in proximal and distal neoplasms.