DNMT1 and breast cancer: Here we use treatment with the DNMT1 inhibitor, 5-Aza-2′-deoxycytidine or decitabine (5-Aza-dC) of Tamoxifen-sensitive (ERpos, MCF7) and -resistant (ERneg, TMX2-28) cell lines to show that inhibition of methylation affects proliferation only in the cell line model for ERneg, Tamoxifen-resistant breast cancer.