Until recently, the diagnosis of prostate cancer (PCa) was based on measuring the concentration of prostate-specific antigen (PSA) in blood, a pathological examination of biopsy material, positron emission tomography (PET) imaging of metabolic activity using 18F-flourodeoxyglucose (FDG) or 11C-acetate, and proliferation activity using radiolabeled choline [1,2]. Here, KLK3 is linked to prostate cancer.