Several genes in breast cancer exhibit CpG island hypermethylation, and in several instances, aberrant activity of DNA methyltransferases led to the hypermethylation and silencing of HOXA5, TMS1, p16, RASSF1A, and BRCA1 genes with tumour suppressor behavior [11,13,75,161,162,163]. The gene discussed is BRCA1; the disease is breast carcinoma.