In serum, the prostate-specific antigen (PSA; kallikrein 3) protein is the most widely studied biomarker in PCa as either a single marker (total PSA or -2 pro PSA) or a combined marker in the Prostate Health Index (PHI: free PSA, total PSA, -2proPSA) or 4kscore (total PSA, free PSA, intact PSA, and human kallikrein 2) [7]. The gene discussed is KLK3; the disease is posterior cortical atrophy.