Volume-based evaluation of serum assays for new prostate-specific antigen isoforms in the detection of prostate cancer

Objectives. Recently, disease-specific isoforms of the prostate-specific antigen (PSA) have been identified. We evaluated the efficacy of precursor isoforms of PSA (pPSA) and an internally cleaved form of PSA referred to as the benign prostatic hyperplasia-associated PSA (BPSA) for the detection of prostate cancer. Methods. Serum concentrations of [-21, [-4], and [-7]pPSA, sum pPSA [-2] + [-4] + [-7]pPSA), and BPSA were retrospectively measured in 43 selected men. The median total PSA levels in men with and without cancer were 6.5 mug/L (range 0.4 to 12.1 mug/L) and 6.1 mug/L (range 3.7 to 21.5 mug/L, respectively. Of the 43 men, 15 had clinical T2 prostate cancer with an ultrasound-estimated prostate volume (PV) of greater than 50 mL, 13 had clinical T2 prostate cancer with PV less than 25 mL, and 15 were prostate cancer free with PV greater than 50 mL. Results. The median values for BPSA, free-to-total PSA ratio (f/tPSA), and benign-to-total PSA ratio (B/tPSA) differed statistically between men with cancer and a PV less than 25 mL and men with cancer and a PV greater than 50 mL (P <0.05) and between the men with cancer and a PV less than 25 mL and men without cancer and a PV greater than 50 mL (P <0.005). All evaluated variables had no correlation with tumor volume in 15 men who had undergone radical prostatectomy. Conclusions. In this preliminary study, the level of [-21, [-4], sum pPSA, and BPSA seemed to be PV related, but only BPSA and B/tPSA and f/tPSA were significantly associated with PV. Therefore, pPSA did not aid in better discriminating cancer from noncancer.