Frequent loss of a p53 allele in carcinomas and their precursors in ulcerative colitis.

Allelic deletions of the p53 gene previously were demonstrated by Southern hybridization to occur in high frequency in sporadic colon carcinomas and in a variety of other human tumors. We have examined the frequency of allelic loss of the p53 gene in carcinoma and dysplasia arising in patients with chronic ulcerative colitis who are heterozygous for the codon 72 polymorphism in exon 4 of the p53 gene. Cells derived from carcinoma and dysplasia specimens from 10 patients who were heterozygous at this locus were sorted by flow cytometry on the basis of DNA content. The p53 exon 4 region was amplified from diploid and aneuploid populations, via a polymerase chain reaction (PCR), and digested with BstUI. Three of three carcinomas, four of six dysplasias, and one patient who was indefinite for dysplasia demonstrated evidence of allelic loss of the p53 gene. Seven of ten cases of sporadic colon carcinoma, analyzed for comparative purposes, exhibited loss of a p53 allele. These results demonstrate that PCR analysis, followed by restriction endonuclease digestion of a polymorphic locus, can provide a rapid, definitive method for analyzing loss of heterozygosity in small numbers of cells from colonic mucosa. Such loss precedes cancer in ulcerative colitis and can be present in its earliest histologically identifiable precursor.