NCIt definition : An assay system that indirectly measures the amount of three forms of prostate-specific
antigen (PSA) in a patient serum sample and then uses those values to calculate a
score that estimates the patient's probability of having prostate cancer. The PSA
forms that are examined are total PSA, free PSA, and an isoform of PSA that has a
propeptide comprised of two amino acid residues ([-2]proPSA).;