While normally confined within theprostate, small quantities of PSA can be detected in semen and blood.In serum, a minor fraction of PSA is present in its free form (fPSA),while the predominant molecular form is an 80–90 kDa complexof PSA with α1-antichymotrypsin.10 PCa alters the microarchitecture within the prostate, which leadsto higher quantities of PSA leaking out into the blood. Here, KLK3 is linked to posterior cortical atrophy.