To understand the current research status on gene-specific DNA methylation in blood-based DNA as a screening biomarker for breast cancer early detection, we reviewed recent studies which investigated blood-based DNA methylation of BRCA1, APC, RARB, ESR1, CDH1, SYK, TIMP3, GSTP1, DAPK, and IGF2 between BC patients and healthy controls [38]. This evidence concerns the gene ESR1 and breast cancer.