Abstract 3754: DNA methylation in hepatocellular carcinoma

Abstract

Abstract Hepatocellular carcinoma (HCC) is the third most common cause of cancer death in the world. In the last three decades, HCC incidence has been increasing throughout the western world and research to uncover molecular mechanisms and markers of the disease has expanded. DNA methylation is a relevant molecular alteration in liver carcinogenesis. We carried out a retrospective study of 31 HCC cases to better understand the role of promoter methylation and global methylation changes in association with viral status, smoking exposure and other clinicopathological characteristics of HCC. Levels of DNA methylation were determined by pyrosequencing in DNA extracted from tumor and non-tumor adjacent tissue. We selected a panel of genes previously found to be implicated in epigenetic changes during liver carcinogenesis. The promoter regions of P16, APC, RASSF1A, CHGA and TP73 were investigated and the promoter region of the interspersed repetitive element LINE1 was used as a marker of global DNA methylation. We found statistically significant differences between the levels of DNA methylation in tumor and non-adjacent tumor tissue for P16, APC and TP73. Elevated methylation percentages were found for all markers in tumor tissue when compared to the corresponding non-tumor tissue DNA (P16tumor =35.9% vs. P16normal =4.9%, p<0.0001; APCtumor =42.1% vs. APCnormal =12.5%, p<0.0001; TP73tumor =37.7% vs. TP73normal =23.6%, p=0.007). Global methylation levels as measured by LINE1, were significantly lower in tumor tissue than in non-tumor adjacent tissue DNA (LINE1tumor =55.9% vs. LINE1normal =72.7%, p<0.0001). Statistically significant differences were also found between smokers and non-smokers in the levels of global DNA methylation of tumor tissue DNA (LINE1non-smokers = 60.30% vs. LINE1smokers=69.04%, p=0.05). Additional research into the association between DNA methylation and viral hepatitis status revealed no statistically significant differences between HCV carriers and non-carriers for any of the methylation markers studied. Clinicopathological characteristics of these patients were also analyzed in association with DNA methylation. Differences in tumor stage and survival were not associated with a statistically significant difference in DNA methylation percentages of tumor tissue DNA for these markers. However, CHGA promoter methylation was statistically significantly higher in low grade tumors than high grade tumors (CHGAgrade >2 = 19.83% vs. CHGAgrade ≤2 = 22.11%, p=0.04). Our results suggest that smoking might affect epigenetic mechanisms involved in liver carcinogenesis, and revealed potentially new prognostic epigenetic markers. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 3754. doi:10.1158/1538-7445.AM2011-3754