KLK3 and neoplasm: Similar to clinical tumor markers, such as prostate-specific antigen, which are routinely used in patients for cancer screening or therapy monitoring, xenograft growth induced by transplanted tumor cells expressing a secreted luciferase from the marine copepod Gaussia princeps (GLuc) can be quantitatively monitored based on GLuc activity levels determined ex vivo in small-volume blood or urine samples [20–26].