KLK3 and cancer: Clinically validated protein-based biomarkers such as human epidermal growth factor receptor 2 (HER2), prostate-specific antigen (PSA), cancer antigen 125 (CA125), carcinoembryonic antigen (CEA), and alpha-fetoprotein (AFP) are already widely used for early detection, prognosis, and monitoring of therapeutic efficacy across various cancer types (Table 1) [50].