Purpose: Prostate-specific antigen (PSA) test has become a widely used screening test in prostate cancer (CaP). However, low specificity of serum PSA leads to many false-positive and false-negative results and clinical uncertainty. Development of CaP-specific diagnostic and prognostic markers is needed. Detection of circulating PSA-expressing cells (CPECs) in blood and bone marrow of CaP patients has potential in molecular diagnosis and prognosis. Our novel observations of the frequent presence of CPECs in CaP patients with organ-confined disease by reverse transcription (RT)-PCR-PSA assay in epithelial cells enriched from peripheral blood (ERT-PCR/PSA) have led us to test the hypothesis that CPECs have diagnostic potential for CaP.
Experimental design: Epithelial cells from peripheral blood of radical prostatectomy patients or prostate biopsy patients were isolated using antiepithelial cell antibody, Ber-EP4-coated magnetic beads, and total RNA specimens from these cells were analyzed for PSA expression by RT-PCR.
Results: Peripheral blood specimens of 108 of 135 (80.0%) CaP patients were positive in ERT-PCR/PSA assay. Peripheral blood specimens from 45 control men were virtually negative (97.8%). In the blinded investigation, 84 patients who had biopsy for suspicion of CaP were evaluated by ERT-PCR/PSA assay. Eighteen of 22 (81.8%) patients with biopsy-proven CaP were positive, and 54 of 62 (87.1%) patients with biopsy negative for CaP were negative in this assay (P < 0.001).
Conclusions: Our study provides intriguing novel results showing that the majority of patients with clinically organ-confined CaP contain CPECs. Strong concordance between the biopsy results and ERT-PCR/PSA assay (sensitivity 81.8%; specificity 87.1%) suggests a potentially new diagnostic application of this type of assay in CaP diagnosis.