ESR1 and breast cancer: In previous studies, we identified a subset of breast cancer cell lines and primary breast cancers that exhibit aberrant DNA hypermethylation that results in concurrent epigenetic silencing of multiple methylation-sensitive genes (including CEACAM6, CDH1, CST6, ESR1, GNA11, MUC1, MYB, TFF3 and SCNN1A) secondary to DNA methyltransferase enzyme hyper activity associated with overexpression of DNMT3b (12).