Association of p53 accumulation with TP53 mutations, loss of heterozygosity at 17p13, and DNA ploidy status in 273 colorectal carcinomas

The aim of this study was to establish an experimentally based cutoff level for assessing p53 immunoreactivity in colorectal tumors. The accumulation of p53 protein in 273 colorectal tumors was correlated with previously obta ined data on TP53 mutation and loss of heterozygosity at two 17p13 loci in the same tumors. The monoclonal antibody PAb 1801 was used for p53 staining , and the results obtained by immunohistochemistry and immunoblotting were similar. Mutation analyses of exons 5-8 were performed using constant denat urant gel electrophoresis followed by sequencing. There were no statistical ly significant differences for any measured TP53 gene alteration between th e group of tumors without p53-positive nuclei (n = 83) and the group with < 5% positive nuclei (n = 58). The majority of mutations within these groups were deletions/insertions and nonsense mutations without p53 accumulation. Therefore, we assume that 5% p53-positive nuclei is the relevant cutoff lev el to assess TP53 damage in colorectal tumors. A prerequisite for this reco mmendation is optimal conditions for p53 protein detection. The parameters for p53 dysfunction were correlated to DNA aneuploidy measured by flow cyto metry. TP53 mutations were significantly associated with DNA aneuploidy (P < 0.00001), and a nonrandom distribution of TP53 gene alterations among dip loid (DI = 1), hyperdiploid (1.0 < DI < 1.3), and highly aneuploid (DI > 1. 3) tumors indicates that DNA hyperdiploid tumors constitute a separate deve lopmental entity different from tumors with gross aneuploidy.