DNMT1 and breast cancer: Epigenetic silencing of tumour suppressors by CpG island hypermethylation is a common hallmark of cancer,42 and OCT4 directly binds to the promoter of DNMT1 and enhances its expression in mesenchymal stem cells.43 DNMT1 is required to maintain DNA methylation patterns in mammalian cells and is thought to be the predominant maintenance methyltransferase gene.44 The estrogen receptor alpha (ERα) is considered to be involved in breast cancer progression.45 ERα modulates transcription by forming complexes with other proteins and then binding to the estrogen response elements (EREs).