Simultaneous Quantification of Prostate-specific Antigen and Human Glandular Kallikrein 2 mRNA in Blood Samples from Patients with Prostate Cancer and Benign Disease

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Detection or quantification of circulating cancer cells has been proposed as an aid in detection and monitoring of several solid tumors. We investigated the classification accuracy of prostate-specific antigen (PSA) and human glandular kallikrein 2 (hK2) mRNA copy numbers in blood for the differentiation of patients with prostate cancer (PC) and benign disease. PSA and hK2 mRNA expression was studied in blood samples from 51 men with PC and 19 men with benign disease. Among the PC patients, 10 had organ-confined disease (pT1-pT2). We used a multiplexed reverse transcription-PCR assay with two highly target-like mRNA internal standards for the simultaneous quantification of PSA and hK2 mRNA. An external calibration curve covered the range of 10(2)-10(6) mRNA copies. PSA and hK2 mRNA were detected in 41 of 51 (median, 1200 copies/0.5 mL of blood) and 43 of 51 (median, 3800 copies/0.5 mL of blood) patients with PC, respectively, whereas only 1 of 19 men with benign disease was positive for both mRNAs (1500 PSA and 3100 hK2 mRNA copies/0.5 mL of blood; P <0.0001, Mann-Whitney U-test). Of the 10 patients with organ-confined PC, only 3 with low Gleason scores (< or =5) were negative for both PSA and hK2 (P = 0.02, Mann-Whitney U-test). The presence of PC cells in the blood circulation is an early event in PC progression, and quantitative assays for PSA and hK2 mRNA discriminate benign from PC cases. Further studies are needed to determine the diagnostic accuracy and prognostic value of the assays.