First, to confirm the presence of hypermethylation in the CDO1 promoter region in serum cfDNA of BC patients, we performed the MethyLight assay to measure the PMR of CDO1 in cohort II, which included serum samples from 113 BC patients (stages I–IV) and 68 control patients (31 normal individuals and 37 patients with breast benign diseases). The gene discussed is CDO1; the disease is breast fibrocystic disease.