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Background: Epigenetic silencing of tumor-related genes, due to CpG island methylation, is considered to be an important mechanism for the development of many tumors, including gastric cancinoma. DNA methylation of multiple CpG sites in promoter regions of several tumor related genes, such as hMLH1, p14, p16, and APC has reported in gastric carcinoma. Recent studies indicate that aberrant CpG island methylation, and subsequent silencing of the COX-2 promoter, has been observed in a subset of gastric carcinomas (GC). To determine the occurrence of CpG island hypermethylation in GC in relation to H. pylori infection, the status and level of CpG methylation in promoter region of COX-2 was analyzed in early and advanced gastric carcinomas as opposed to normal gastric tissues. Materials and Methods: The extent of promoter methylation of COX-2 gene was assessed quantitatively using Pyrosequencing (PS) in 60 early gastric cancers (EGC) and 60 advanced gastric cancers (AGC) samples harvested upon gastrectomy, and 40 normal gastric mucosa samples from patients with benign gastric pathology. Giemsa stain was performed to detect H. pylori in neoplastic and non-neoplastic gastric mucosa. Gene product was studied by immunohistochemistry and the relationship between methylation profile of gene promoter and clinicopathological parameters was analyzed. Results: The PS analysis of GCs revealed a high frequency of COX-2 methylation in 30.0% (36/120). The methylation frequency for COX-2 gene by PS techniques was significantly higher in EGCs than in AGCs (40.0% and 20.0%, respectively, p<0.05) There was a significant difference of COX-2 methylation in between GCs and normal gastric tissues (30.0% vs. 10.0%, respectively by PS, p<0.05). The mean methylation level in 8 CpG sites of COX-2 promoter by PS was 19.9%, 33.5%, and 18.5% in normal gastric tissue, EGCs, and AGCs respectively. COX-2 gene methylation was significantly associated with H. pylori infection (p<0.001). However, the methylation of COX-2 promoter by PS was not correlated with reduced or absent expression of COX-2 protein (p>0.05). Conclusion: we found that COX-2 promoter methylation was significantly higher in the tumor tissues and was early event for gastric carcinoma development, but not in progression of GC. These results suggest that COX-2 gene methylation may be important in the initial development of gastric carcinogenesis and the H. pylori infection is associated with promoter methylation of COX-2 gene. Furthermore, standard PCR followed by PS could be a more specific and quantitative method providing a more comprehensive picture of the distribution of DNA methylation throughout the promoter regions of specific genes, which will be of benefit in oncology research. Note: This abstract was not presented at the AACR 101st Annual Meeting 2010 because the presenter was unable to attend. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 157.

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