It has been shown that DNMT-inhibiting cytosine nucleoside analogs, decitabine, azacitidine, and zebularine, have a significant effect on several cancers such as myeloid leukemia (AML) (Flotho et al., 2009), breast cancer (Chen et al., 2012), gastric cancer (Tan et al., 2013), colorectal cancer (His et al., 2005), endometrial cancer (Cui et al., 2010), lung cancer (Luszczek et al., 2010), colorectal cancer (Xiong et al., 2009), and prostate cancer (Walton et al., 2008). This evidence concerns the gene DNMT1 and breast cancer.