Mastoraki, S. Strati, A. Tzanikou, E. Chimonidou, M. Politaki, E. Voutsina, A. Psyrri, A. Georgoulias, V. Lianidou, E., ESR1 methylation: A Liquid biopsy-based epigenetic assay for the follow up of patients with metastatic breast cancer receiving endocrine treatment: Short running title: Liquid biopsy: ESR1 methylation in CTCs and paired ctDNA, Clinical Cancer Research, (24), 1500-1510, 2018, American Association for Cancer Research Inc., 1078-0432