Prognostic values of 5-hmC, 5-mC and TET2 in epithelial ovarian cancer

DNA methylation is an important epigenetic modification that is frequently altered in cancer. Recent reports showed that the level of 5-hydroxymethylcytosine (5-hmC) was altered in various types of cancers. The influence of DNA methylation in epithelial ovarian cancer (EOC) is not fully understood. Therefore, the aim of the present study was to investigate factors involved in DNA demethylation in EOC compared with normal ovarian tissues. We examined the expression of 5-hmC, 5-mC, and TET2 by immunohistochemistry in 130 cases of EOC and 40 cases of normal ovarian tissues. We assessed the prognostic values of 5-hmC, 5-mC, and TET2 in clinical outcome of EOC. We discovered a significant decrease in 5-hmC and TET2 expression in EOC compared with normal ovarian tissues. In contrast, there was a significant increase in 5-mC expression in EOC compared with normal ovarian tissues. The expression of 5-hmC, 5-mC, and TET2 correlated with pathologic stage, tumor grading, lymph node metastasis, and vascular thrombosis. Furthermore, decreased level of 5-hmC predicts poor prognosis of EOC patients. The expression of 5-hmC was an independent prognostic factor for overall survival of EOC patients. The data suggest that loss of 5-hmC is an epigenetic event of EOC, and the expression of 5-hmC could serve as a prognostic factor for EOC.