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Aim: To study the hypermethylation of RASSF1A gene, the expression of RASSF1A protein, and correlation between them and the clinicopathological features of GB cancer.

Methods: Formalin-fixed, paraffin-embedded tumors and non-neoplastic GB tissues [22 carcinomas, 8 adenomas, 26 normal epithelia] were collected from patients who had undergone surgical resection. The methylation status of two region of the RASSF1A CpG islands was determined by methylation-specific PCR (MSP) and the expression of RASSF1A protein was examined by immunohistochemistry using tissue microarrays. K-ras mutation was analyzed by direct sequencing.

Results: Methylation of RASSF1A promoter region 1 was detected in 22.7% (5/22) of carcinomas, 12.5% (1/8) of adenomas, and 0% (0/26) of normal gallbladder epithelium, respectively (P=0.025). Methylation of the first exon region 2 was found in 36.4% (8/22) of carcinomas, 25.0% (2/8) of adenomas, and 8.0% (2/26) of normal gallbladder epithelium, respectively (P=0.038). K-ras mutations were present in 4.5% (1/22) of carcinoma and 25% (2/8) of adenoma. RASSF1A methylaton was not associated with clinicopathological factors and K-ras mutation. Reduction or loss of RASSF1A expression was observed in most methylated adenocarcinomas. In RASSF1A-expressing three human biliary tract cancer cell lines contained unmethylated promoter and exon 1.

Conclusion: Downregulation of RASSF1A expression through DNA hypermethylation may play a role in GB carcinogenesis and RASSF1A hypermethyaltion could be a reliable marker for GB cancer.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA