Thus, we confirmed that the promoter CpGI of WNT1 was hypermethylated in the cfDNA of patients with metastatic LBBC and that this aberrant methylation showed a high diagnostic accuracy to detect this BC subtype, suggesting that the hypermethylation of WNT1 could be a suitable biomarker for cancer detection and monitoring of metastatic patients. The gene discussed is WNT1; the disease is breast cancer.