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). The gene discussed is MUC1; the disease is breast carcinoma.