TP53 inactivation and expression of methylation-associated proteins in gastric adenocarcinoma with enteroblastic differentiation.

Gastric adenocarcinoma with enteroblastic differentiation (GAED) is a rare variant of aggressive adenocarcinoma. We demonstrated previously that GAED is genetically characterized by frequent TP53 mutation. In this study, we aimed to further clarify the mechanism of inactivation of TP53 in GAED in the light of promoter methylation of TP53, and expression of methylation-associated proteins such as Ten-eleven translocation (TET) 1 and 5-hydroxymethylcytosine (5-hmc) in addition to ATM mutations. We analyzed 51 cases of GAED. The ATM mutation was detected in only one case. Promoter methylation of TP53 was detected in 18% and frequency of loss of heterozygosity (LOH) at TP53 locus was 37.2%. Reduced TET1 expression was found in 29 cases (56.9%) and was significantly associated with advanced stage (p = 0.01), lymph node metastasis (p = 0.04), and macroscopic type (p = 0.01). Reduced 5-hmc expression was found in 28 cases (54.9%) and was significantly associated with advanced stage (p = 0.01), gender (p = 0.01), tumor location (p = 0.03), tumor size (p = 0.01), and lymph node metastasis (p = 0.01). Among 9 cases with TP53 promoter methylation, reduced expression of TET1 was observed in 6 cases, and reduced expression of 5-hmc was observed in 5 cases. Reduced expression of both TET1 and 5-hmc was significantly associated with adverse clinical outcomes. In summary, promoter methylation of TP53 is partly involved in loss of p53 expression. Aberrant methylation by reduced TET1 and 5-hmc may be involved in the development of aggressive GAED.