We next analyzed the DNA methylation levels of RNF144A promoter at the R1 and R2 regions by pyrosequencing in normal mammary epithelial cell line HBL100 and 5 representative breast cancer cell lines, including MCF7, T47D (luminal‐type), MDA‐MB‐453 (HER2‐positive), BT20, and MDA‐MB‐231 (TNBC). Here, ERBB2 is linked to breast cancer.