To investigate the clinical utility of the subforms of free prostate-specific antigen (PSA), namely proPSA and "benign" PSA (BPSA), to improve cancer detection when the percent free PSA level is less than 15%. Percent free PSA, while maintaining sensitivity, has greatly improved the specificity of PSA for the early detection of prostate cancer. A low percent free PSA value indicates a greater risk of cancer, but only 30% to 50% of men with percent free PSA levels of less than 15% actually have cancer at biopsy. Archived sera from 161 consecutive men who were prospectively enrolled in our Early Detection Research Network prostate cancer early detection biomarker program with a percent free PSA value of less than 15% were included in the study. Total PSA, free PSA, proPSA, and BPSA were measured for each sample. The mean total PSA was 6.1 ng/mL (range 1.8 to 24.0). The mean age of the study group was 62 ± 7 years. Prostate cancer was detected in 66 (41%) of 161 men. The area under the curve-receiver operating characteristic for total and percent free PSA was 0.51 and 0.54, respectively. BPSA and proPSA/BPSA both improved cancer detection compared with percent free PSA alone; the improvement was statistically significant (P <0.001). The area under the curve-receiver operating characteristic for proPSA/BPSA was 0.72, giving a sensitivity and specificity of 90% and 46%, respectively. The results of our preliminary studies have suggested that the ratio of proPSA and BPSA can distinguish cancer with greater accuracy when the percent free PSA value is very low (less than 15%), and may, therefore, provide better clinical utility in this lower range of percent free PSA.
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