KLK3 and benign prostatic hyperplasia: PSA exists in the bloodstream in several specific forms, including free and complexed (e.g., α-1-antichymotrypsin) forms; free PSA is composed of three isoforms: i-PSA (inactive PSA), pro-PSA (proenzyme PSA), and BPH-PSA (benign prostatic hyperplasia-PSA).