Transcriptionally silenced genes have a repressive epigenetic state that compacts chromatin. Repressive epigenetic marks include non-acetylated histones, lysine methylation at H3K27 and H3K4 and cytosine methylation at CpGs21. Active DNA demethylation is tightly regulated and requires a series of enzymatic reactions that proceed through the BER pathway. This mechanism of epigenetic alteration is likely responsible for upregulation of pro-tumorigenic genes, as it has been identified for dynamic, context dependent modification of DNA22, 23.