KLK3 and neoplasm: CTCs also exhibit some unique biochemical properties attributed to the specific tumor markers expressed by CTCs, which can be used to distinguish CTCs from other cells, such as epithelial cell adhesion molecules (EpCAM) and cytokeratin (CK), as well as prostate specific antigen (PSA), epidermal growth factor receptor (EGFR) and carcinoembryonic antigen (CEA), etc. [28,29,30].