Objectives: Inactivation of the p53 tumor suppressor gene is considered to be a late event involved in the malignant transformation of colorectal adenoma to cancer. Thus, its detection is thought to provide useful information for the clinical management of colorectal neoplasms. We devised a rapid screening test for allelic loss of the p53 gene by non-radioisotopic single-strand conformation polymorphism analysis.
Methods: Biopsy materials from 119 colorectal tumors obtained at endoscopy were examined. Three intragenic polymorphic sites were amplified by polymerase chain reaction using DNA extracted from these materials, and amplified DNA fragments were subjected to non-radioisotopic single-strand conformation polymorphism.
Results: This method can detect a loss of heterozygosity (LOH) of the p53 locus from samples containing over 40% tumor derived DNA, and the combination of the three polymorphic markers encompassed 62.4% of Japanese patients as informative. In adenocarcinoma, an LOH was detected in 51.5% (17 of 33) of the samples and in 12.2% (4 of 33) of tubular and/or tubulovillous adenomas. The p53 gene was mutated only in samples carrying an LOH, that is 64.7% (11 of 17) of carcinomas and 25.0% (1 of 4) of adenomas, but there were no mutation in samples retaining both alleles. The presence of an LOH was statistically correlated both with p53 mutation and malignant histology (chi 2 test, p < 0.05).
Conclusions: This method can detect LOH from biopsy material obtained at endoscopy. LOH in the p53 locus precedes mutation of the p53 gene, and its detection provides useful information of malignancy in colorectal tumors.