Promoter methylation caused by overactive DNA methyltransferases has been implicated in the silencing of ~75 key tumor suppressor genes (TSG) related to breast tumor genesis; these include genes for cell cycle regulation, DNA repair, breast cancer (BRCA1, BRCA2), cell-signaling pathways, and estrogen-α and progesterone receptors [15]. Here, BRCA1 is linked to breast cancer.