A RETROSPECTIVE AND PROSPECTIVE OVERVIEW OF PROSTATE-SPECIFIC ANTIGEN

Since the identification of prostate-specific antigen (PSA), continued technological advances have provided highly sensitive assays for its quantification. Given its lack of disease specificity, and its recent detection at low levels in an increasing number of non-prostatic tissu es, PSA is far from being the perfect ''tumour'' marker (biological ma rker). However, the positive predictive value of PSA for assessing can cer risk makes PSA the most useful ''tumour'' marker for monitoring pr ogression and response to treatment among patients with prostate cance r. Earlier detection through screening for elevated levels of PSA, whi le controversial, has been proposed as a way to decrease prostate canc er mortality. Haematogenous identification of PSA mRNA may provide sta ge-related prognostic information, and the use of ultrasensitive assay s for PSA may permit earlier identification of residual or recurrent c ancer, following treatment and the initiation of adjuvant therapy. Var ious PSA-related concepts, including the ratio of ''free'' PSA and com plexes of PSA with the protease inhibitor, alpha(1)-antichymotrypsin, to total PSA, have been proposed and placed within diagnostic and mana gement algorithms. Elevations of PSA in other irregularities of the pr ostate, notably in benign prostatic hyperplasia, and the increasing fr equency and number of non-prostatic tissues, including those in women, expressing PSA, have implications for future immunoassays for PSA and strategies for immunotherapy using PSA-based monoclonal antibodies or vaccines, as well as for the molecular basis for its anomalous expres sion and physiological function(s).