KLK3 and cancer: In addition to the classic circulating biomarkers useful for cancer patients’ follow-up and diagnosis, such as the carcinoembryonic antigen (CEA) or the prostate-specific antigen (PSA), whose importance in routine oncology is well established, the liquid biopsy (LB) approaches include the detection of circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), circulating miRNAs and tumor-derived extracellular vesicles (EVs).