p53 overexpression as a marker of malignancy in gastric biopsies

Inactivation of the p53 tumour-suppressor gene is the commonest genetic abnormality in human cancers. This results in a conformational change in the p53 protein, and a consequent prolongation in its half-life; thereby permitting the identification of p53 immunoreactivity in malignant cells. Such reactivity is observed in up to 57% of gastric carcinomas, and is a proven indicator of poor prognosis. We have investigated the use of p53 immunohistochemistry in the diagnosis of malignancy in pre-operative gastric biopsy specimens. Using a three-stage immunoperoxidase technique, p53 expression was examined in 117 gastric biopsies obtained during flexible upper gastrointestinal endoscopy: 80 of these biopsies were from known gastric carcinomas, 20 from benign gastric disorders and 17 from normal gastric mucosa. Of the gastric cancers 40% (n = 32) exhibited overexpression of p53. No reactivity was observed in any of the biopsies of gastric ulcers, polyps or normal mucosa. The expression of p53 by gastric carcinomas improved the diagnostic accuracy of conventional histopathology from 86% to 92.5%; with 5% of biopsies incorrectly diagnosed and 2.5% of an equivocal appearance. These results demonstrate that the detection of p53 is a highly specific marker of gastric malignancy, and that such a technique can easily be performed on biopsies obtained at endoscopy.