MUTATION ANALYSIS OF THE P53, APC, AND P16 GENES IN THE BARRETTS-ESOPHAGUS, DYSPLASIA, AND ADENOCARCINOMA

Aims-To study the loss of heterozygosity and the presence of mutations at the p53, p16/CDKN2, and APC genes in Barrett's oesophagus, low gra de dysplastic oesophageal epithelium, and adenocarcinoma of the oesoph agus; to relate the presence of alterations at these genes with the pr ogression from Barrett's oesophagus to adenocarcinoma. Methods-DNA was extracted from paraffin blocks containing tissue from Barrett's oesop hagus (12 samples), low grade dysplasia (15 cases), and adenocarcinoma (14 cases). Loss of heterozygosity (LOH) at the p53, p16, and APC gen es was determined by comparing the autoradiographic patterns of severa l microsatellite markers between the normal tissue and the malignant t issue counterpart. SSCP was used to determine the presence of mutation s at p53 (exons 5 to 8), p16 (exon 2), and AFC. Homozygous deletion of the p16 gene was defined through polymerase chain reaction followed b y Southern blot. Results-LOH at the p53, p16, and APC genes was not ob served in Barrett's oesophagus without dysplasia, and increased to 90% (p53), 89% (p16), and 60% (APC) in the adenocarcinomas. The p53 gene was mutated in only two adenocarcinomas (codons 175 and 245). In one c ase a mutation at the APC gene (codon 1297) was found. No patient had mutation at the second exon of p16. However, this gene was homozygousl y deleted in three of the 12 adenocarcinomas. Conclusions-The tumour s uppressor genes p53, p16, and APC are often deleted in adenocarcinomas derived from Barrett's oesophagus. Mutations at these genes are also found in the adenocarcinomas, including the homozygous deletion of the p16 gene. However, the absence of genetic alterations in the Barrett' s oesophagus and the low grade dysplastic epithelia suggest that mutat ions at these genes develop later in the progression from Barrett's oe sophagus to adenocarcinoma.