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LINE- 1 hypomethylation level as a potential prognostic factor for epithelial ovarian cancer

A genome-wide hypomethylation is a common and crucial event in cancer. This study was to evaluate common epithelial ovarian cancer (EOC) if long interspersed element-1 (LINE-1) repetitive sequences methylation levels are progressively decreased during multistage carcinogenesis and there are the correlation between LINE-1 methylation levels and clinicopathologic characteristics. A total of 59 pairs of microdissected EOC tissues obtained from patients with EOC were examined for the methylation levels of LINE-1 repetitive sequences by a COBRALINE-1 (combined bisulfite restriction analysis of LINE-1) PCR protocol. The methylation levels were correlated with clinicopathologic parameters to determine the potential role of global hypomethylation as a prognostic marker for EOC. The LINE-1 methylation levels of 59 EOCs, 34.87 ± 7.39%, were lower than in representative normal ovarian tissues (46.89 ± 8.31%; 95% CI: 9.42–14.62; P< 0.001, paired-two-tailed t test). A decrease in the LINE-1 level of methylation was correlated with histological subtypes, higher FIGO and advanced tumor grade. Patients with greater hypomethylation (i.e., a methylation level ≤ 34.87%) had poorer mean overall survival (P= 0.003) and a lower mean progression-free interval (P< 0.001). Therefore, progressive decrease in LINE-1 methylation level is a common and important epigenetic process in ovarian multistep carcinogenesis. Moreover, the COBRALINE-1 method has the potential to be used as a tumor marker for EOC.