EVALUATION OF 6 ANTIBODIES FOR IMMUNOHISTOCHEMISTRY OF MUTANT P53 GENE-PRODUCT IN ARCHIVAL COLORECTAL NEOPLASMS

Immunohistochemical detection of intranuclear p53 gene product may ind icate mutation of the p53 suppressor gene on chromosome 17p. We used s ix commercially available antibodies for p53 immunohistochemistry on 1 9 archival colorectal neoplasms and compared the results with the muta tion status of the p53 gene and 17p allelic deletion status. By Friedm an's ranking analysis, use of mouse monoclonal antibody DO7 with Targe t Unmasking Fluid (TUF) for antigen retrieval was the most sensitive a nd specific procedure (P<0.0001). Six of 7 cases with high expression (p53 Labeling Index >30 per cent using a CAS 200 image analyser) had p 53 mutation. Of seven tumours without expression (LI <1 per cent), six had no mutation and one had a truncating mutation which prohibited nu clear localization of gene product. The low expression group (1 per ce nt <LI <30 per cent, n=5) consisted of three tumours without and two t umours with mutation. The sensitivity of high expression with the DO7- TUF method for p53 gene mutation was 67 per cent with specificity of 9 0 per cent, predictive value of a positive of 86 per cent, predictive value of a negative of 75 per cent and efficiency of 79 per cent. This study suggests that immunohistochemistry is valuable for assessing p5 3 gene mutations in colorectal neoplasms, but further study is needed to elucidate the precise link between immunohistochemistry and molecul ar genetic alterations.