Alteration of aberrant DNA methylation is one of the most consistent epigenetic changes found in human cancers. DNA methylation is catalyzed by DNA methyltransferase (DNMT). In this study, we examined DNMT protein expression by immunohistochemistry in surgically resected hepatocellular carcinomas (HCCs). Sections of paraffin-embedded specimens were obtained from 95 patients with HCC between 1989 and 2002. The specimens were stained with anti-DNMTs (DNMT1, DNMT3a and DNMT3b) antibodies. There were statistically significant associations between DNMT protein expression and tumor differentiation (P < 0.05) and intrahepatic metastasis (P < 0.05). DNMT3a protein expression was significantly correlated with portal vein involvement of tumors (P < 0.05). The overall survival rates of patients with DNMT3a-positive HCCs and DNMT3b-positive HCCs were significantly lower than those of patients negative for these proteins (P < 0.005, respectively). To further evaluate the correlation between DNMT protein expression and patient survival, we classified patients into 3 groups: Group 1, DNMT1(+), 3a(–) and 3b(–); Group 2) DNMT1(+), 3a or 3b(+); and Group 3) DNMT1(+), 3a(+) and 3b(+). The overall survival rate of patients in Group 3 was significantly lower than those of patients in Groups 1 and 2 (P = 0.0009). In conclusion, the results of this study suggest that DNMT1, DNMT3a and DNMT3b are cooperatively involved in determining the extent of HCCs, and that DNMT protein overexpression in HCCs may be a predictive factor for poor survival
