DNMT1-regulated hypermethylation of the TSG RUNX3 promoter region is a new insight and an early event in breast cancer predominantly in TNBC (triple-negative breast cancer) (Widschwendter and Jones, 2002; Jung et al., 2007; Jiang et al., 2008; Subramaniam et al., 2009; Shin et al., 2016). Here, DNMT1 is linked to breast cancer.