A STUDY OF STABILIZATION OF P53 PROTEIN VERSUS POINT MUTATION IN COLORECTAL-CARCINOMA

Abnormalities of the p53 tumour suppressor gene occur in many types of cancer including approximately 60% of colorectal carcinomas. This stu dy investigates in 47 colorectal carcinomas the relationship between s tabilised p53 protein detected by immunocytochemistry (ICC), and p53 m utation. 27 cases stained positively with the antibody PAb1801. Sequen cing of exons 5-8 revealed 19 mutations in 18 of these cases (one tumo ur contained two different mutations). A rapid, non-radioactive method was developed to screen for mutations in this region of the gene invo lving Single Strand Conformational Polymorphism analysis (SSCP) and a MspI restriction digestion. This screen detected 17/19 (89%) of the se quenced mutations, and a further four mutations in 20 PAb1801 negative cases that were confirmed by sequencing. Reproducibility of ICC in de tecting stabilised protein was assessed by restaining the 47 cases wit h the antibody DO7 after pre-treatment to optimise detection. Fewer ca ses were negative with DO7 although overall concordance with PAb1801 w as good. A substantial proportion of carcinomas with stabilised p53 as detected by ICC do not contain mutations in exons 5-8, whilst some mu tations (the majority in exon 6) are not associated with stabilisation .