[Immunochemical evidence of a mutated p53 protein expressed in human colorectal adenocarcinoma]

Evidence is accumulating that the p53 anti-oncogene is a key gene in the genesis of carcinoma in human colon and rectum. Although mutations of the p53 gene have been shown to be frequent, the protein was present in only approximately 50 percent of specimens examined. However only one monoclonal antibody recognizing an epitope present on wild-type p53 had been used. We studied the p53 expression in a series of 16 colorectal carcinoma specimens using 3 different monoclonal antibodies (pAb 421, 1801, 240). Specific immunofluorescent staining was quantified by dual parameter (DNA/p53) flow cytometry. Two different types of preparations were compared in order to verify the conservation of the antigen. Nuclear suspensions prepared from frozen tumor fragments were shown to produce results equivalent to those of whole cell preparations originating from fresh surgical specimens. The p53 protein was detected in 9 of the 16 cancers with pAb 421 and 240 monoclonal antibodies (8 of which were also positive for pAb 1801 antibody). Four additional tumors were considered positive for pAb 240 antibody alone. Overall, 13/16 cancer specimens were shown to present immunoreactivity for pAb 240 antibody. Topography of staining was investigated by immunohistochemistry with peroxidase methods. Eight cases were informative, 6 of which presented nuclear staining compatible with the cytometry results. There was one discordant case i.e. pAb 240 antibody being positive on cytometry and entirely negative on immunohistochemistry. This small series allowed us to show that 81 percent of tumor samples stained with monoclonal antibody pAb 240, considered to be specific to mutated protein, and that some tumors express a p53 protein which is not detected with terminal sequence-specific antibodies.