Genetic alterations during neoplastic progression in Barrett's esophagus

The aim of our study was to better understand the molecular mechanisms during neoplastic progression in Barrett's esophagus, mainly focusing on p 16 gene transcriptional silencing and the role of disruption of the APC/Β-catenin/Tcf pathway. In addition. expression and mutation of p53 during the neoplastic progression from Barrett's esophagus to adenocarcinoma was characterized and an evaluation of the correlation between gene mutation and/or protein accumulation with clinicopathological findings and survival was performed. In cbapter 2. a methodological validation of microdissection and DNA extraction from archival tissue sections is reported. This procedure allows 15 PCR reactions to be routinely performed on lesions as small as I mm in diameter. Its usefulness was demonstrated in the study of loss of heterozygosity (LOH) on chromosome 18q. In chapter 3. we established a new method for promoter hypermethylation analysis based on bisufite modification followed by PCR single-strand conformation analysis (MS-SSCA). The application for p 16 gene promoter hypermethylation analysis showed that this approach is rapid. specific. semi-quantitative and works well with DNA extracted from microdissected fixed tissue sections. In chapter 4, we characterized expression and mutation of p53 during the neoplastic progression from Barrett's esophagus to adenocarcinoma. and test the reliability of immunohistochemistry for p53 overexpression as an indicator of p53 mutation in this context. A evaluation of the association of both gene mutation and protein accumulation with clinicopathological findings and survival were also studied. In chapter 5. we determined whether there is a correlation between 13-catenin nuclear accumulation and exon 3 mutation of this gene. Expression and mutation of 13- catenin in the progression of Barrett's esophagus to adenocarcinoma were characterized. In chapter 6. to investigate the potential role of p16 gene inactivation during neoplastic progression in Barrett's esophagus. we analyzed pl6 gene promoter hypermethylation. mutation. LOH of 9p2 J as well as expression of p 16 protein. The relationship among these features was also determined. In chapter 7, our findings are discussed in the context of the current literature.