Our study revealed that the bivalent mark H3K4me3+H3K27me3 was strongly associated with heavy CpG methylation in the 3′-shore of TET1 in GC cell lines, in which TET1 transcription was repressed, supporting previous reports that such bivalent marks are common in adult tumor cells and lead to transcriptional silencing [17, 18]. This evidence concerns the gene TET1 and neoplasm.