Compared to the healthy controls, the methylation levels did not show a significant difference in most of the CpG sites of these genes in the BC cases, except for a few CpG sites including BRCA1 (cg13782816), APC (cg01240931 and cg14511739), ESR1 (cg25565730), CDH1 (cg26508465), and GSTP1 (cg06841499) (see Supplementary Table S4). Here, ESR1 is linked to breast cancer.