Molecular forms of PSA.

Molecular forms of serum PSA (prostate specific antigen) have been developped to improve total PSA sensitivity and specificity in prostate cancer diagnosis and staging. Total PSA is measured in bound (complexed PSA) and unbound (free PSA) molecular forms. Their levels in absolute values and in relation to total PSA (f/t PSA and c/t PSA) have been evaluated. The percentage of free PSA is more specific but less sensitive than tPSA and it is not recommended as a first line diagnostic test. It may be useful as a second-line test, prescribed by the urologist after a first series of negative biopsies. There is general agreement that at high sensitivity, cPSA provides, higher specificity compared with tPSA in the gray zone (2-10 ng/ml). Nevertheless the widespread use of tPSA an the small benefit in terms of specificity explains why cPSA is not generally recommanded. Molecular derivates of tree PSA have been identified : proPSA (precursor inactive form of PSA), intact PSA (an additionnal form of proPSA that is found intact and inactive), human Kallikrein 2 and BPSA (for benign PSA wich is associated to BPH) have been evaluated. Preliminary studies did not have demonstrate their ability to discriminate between cancer and BPH, and did not define cutoff values.