KLK3 and cancer: Following lung cancer, prostate cancer is the second most common cancer and cause of cancer-related deaths in men worldwide.2 At time of bioptic diagnosis, tumor stage and Gleason score76 plus serum PSA (prostate-specific antigen, also known as kallikrein-related peptidase 3, KLK3) are the most accepted predictors of prognosis of prostate cancer.