KLK3 and prostate cancer: Based on prostate specific antigen (PSA) level, tumor grade, and the extent of primary tumor in the prostate gland, clinically localized prostate cancer is classified into low-risk (PSA ≤10 ng/ml, Gleason score ≤6, and stage T1c–T2a), intermediate-risk (PSA >10 but ≤20 ng/ml, Gleason score 7, or stage T2b), and high-risk (PSA >20, Gleason score ≥8, or stage T2c) (2, 3).