KLK3 and prostate cancer: PSA was selected as the third tumor marker because of its importance for the characterization and risk assessment of prostate cancer prior to therapy [40,41,42,43] and to demonstrate the possibility of multiplexed quantification of antigens (AGs) with significantly different sizes (approximate values for the carcinoembryonic antigen (CEA): 180 kDa; neuron-specific enolase (NSE): 95 kDa; and prostate-specific antigen (PSA): 32 kDa).