Figure 4.

Survey of the research development of the molecular forms of prostate-specific antigen (PSA): Approximate years of discovery are indicated on the left. Each box represents a different molecular form of PSA. The Bayer cPSA assay measures PSA bound to α₁-antichymotrypsin (PSA-ACT) and PSA bound to α₁-protease inhibitor (PSA-API). BPSA, BPH-associated free PSA; proPSA, precursor form of free PSA; “intact” PSA, other inactive and intact PSA, which also detects proPSA; PSA-A2M, PSA bound to α₂-macroglobulin. Reprinted, with permission, from Stephan C et al. Urology. 2002;59:2–8.⁸⁶