Evaluation and comparison of two new prostate carcinoma markers - Free-prostate specific antigen and prostate specific membrane antigen

BACKGROUND. Two new prostate cancer markers; free-prostate specific antigen (f-PSA) and prostate specific membrane antigen (PSMA) were recently introduced. This report summarizes a prospective two-year multicenter test of their diagnostic or prognostic capabilities. Total PSA was also measured. METHODS. There were four clinical groups studied: (1) 226 individuals from a screening project undergoing ultrasound and biopsy evaluation had markers obtained: (2) 68 patients suspected of having prostate cancer and undergoing 2 or more biopsies had the markers obtained on multiple occasions: (3) 100 patients undergoing radical prostatectomy had markers obtained pre- and post-operatively: and (4) 31 patients with metastatic prostate cancer each had multiple samples for marker assay obtained over a 2-year period. In all, 465 patients had one or more samples obtained and studied. RESULTS. Free-PSA affords little additional diagnostic advantage compared with total PSA in the screening population. The reciever operating characteristic curves for diagnostic accuracy were ranked: (1) PSA density; (2) total PSA; (3) f-PSA; and (4) PSMA. PSMA showed the best correlation with stage of the primary tumor in the screened group. In the multiple negative biopsy group, f-PSA varied from 12 to 21%. PSMA values were evaluated in all histologic categories. PSA density was greater than or equal to 0.15 in all categories. In the prostatectomy cases PSA values postoperatively were quite low in Stage II; f-PSA was of no value. Later, f-PSA was increased In association with elevated total PSA values. Mean PSMA values were above normal in all postoperative time periods except in Stage III patients at 6 months to 1 year postoperatively. PSA densities were all greater than or equal to 0.15. In patients with metastatic carcinoma, elevated PSMA values correlated best with a poor prognosis (clinical progression), as has been described. CONCLUSIONS. These data suggest that f-PSA values do not provide additional diagnostic benefit compared with total PSA in screening populations, in the presence of suspected cancer, postprostatectomy, or in metastatic disease. PSMA is of prognostic significance, especially in the presence of metastatic disease, and correlates well with the stage of disease in cancers detected in a screened population. (C) 1996 American Cancer Society.