Abstract: Objective To investigate the relationship of gastric carcinogenesis to promoter methylation and expression of the Proto-cadherin-8（PCDH8） gene，as well as to expression of Dnmt1 protein. Method Samples of cancerous and normal gastric mucosa were obtained surgically from 60 patients with primary gastric cancer. Methylation-specific PCR was used to determine the methylation status of the PCDH8 promoter，while immunohistochemistry was used to measure levels of PCDH8 and Dnmt1 proteins. Results Among the 60 patients，33（55.0%） showed a methylated PCDH8 promoter in samples of cancerous tissue，compared to only 2（3.3%） who showed a methylated promoter in normal samples（χ^２=38.76，P＜0.001）.Methylation status of the PCDH8 promoter showed no significant association with patient age，sex，or TNM stage；methylation was， however， associated with lymph node metastasis（χ^２=17.47，P＜0.001）. Gastric cancer tissue showed significantly lower levels of PCDH8 protein than normal tissue（11.7% vs 90.0%，χ^２=73.65，P＜0.001） and significantly higher levels of Dnmt1 protein（73.3% vs 5.0%，χ２=58.79，P＜0.001）.In gastric cancer samples， the level of PCDH8 protein correlated negatively with that of Dnmt1 protein（r=-0.544，P＜0.001）. Conclusion Methylation of the PCDH8 promoter and elevated expression of Dnmt1 may be associated with the occurrence of gastric cancer.

Key words: Gastric neoplasm, Protocadherin 8, Dnmt1, Gene methylation