KLK3 and prostate cancer: PSA, which is the most common prostatic marker, has a high specificity for prostate cancer, but its expression cannot be detected in ~5% of patients with high-grade PCa (Epstein, 1993; Van Der Toom et al., 2019) or, conversely, leads to the overdiagnosis of clinically insignificant cancer (Tan et al., 2019).