Circulating prostate tumor cells detected by reverse transcription-PCR in men with localized or castration-refractory prostate cancer: concordance with CellSearch assay and association with bone metastases and with survival.

BACKGROUND: Reverse transcription-PCR (RT-PCR) assays have been used for analysis of circulating tumor cells (CTCs), but their clinical value has yet to be established. We assessed men with localized prostate cancer or castration-refractory prostate cancer (CRPC) for CTCs via real-time RT-PCR assays for KLK3 [kallikrein-related peptidase 3; i.e., prostate-specific antigen (PSA)] and KLK2 mRNAs. We also assessed the association of CTCs with disease characteristics and survival. METHODS: KLK3, KLK2, and PSCA (prostate stem cell antigen) mRNAs were measured by standardized, quantitative real-time RT-PCR assays in blood samples from 180 localized-disease patients, 76 metastatic CRPC patients, and 19 healthy volunteers. CRPC samples were also tested for CTCs by an immunomagnetic separation system (CellSearch; Veridex) approved for clinical use. RESULTS: All healthy volunteers were negative for KLK mRNAs. Results of tests for KLK3 or KLK2 mRNAs were positive (> or =80 mRNAs/mL blood) in 37 patients (49%) with CRPC but in only 15 patients (8%) with localized cancer. RT-PCR and CellSearch CTC results were strongly concordant (80%-85%) and correlated (Kendall tau, 0.60-0.68). Among CRPC patients, KLK mRNAs and CellSearch CTCs were closely associated with clinical evidence of bone metastases and with survival but were only modestly correlated with serum PSA concentrations. PSCA mRNA was detected in only 7 CRPC patients (10%) and was associated with a positive KLK mRNA status. CONCLUSIONS: Real-time RT-PCR assays of KLK mRNAs are highly concordant with CellSearch CTC results in patients with CRPC. KLK2/3-expressing CTCs are common in men with CRPC and bone metastases but are rare in patients with metastases diagnosed only in soft tissues and patients with localized cancer.

Novel homogenous time-resolved fluorometric RT-PCR assays for quantification of PSA and hK2 mRNAs in blood.

OBJECTIVES: The purpose of this study was to design, validate, and optimize internally standardized real-time quantitative RT-PCR assays and to identify and avoid problems with assay reliability and examine the impact of an exogenous internal standard. DESIGN AND METHODS: The model system consisted of internally standardized quantitative real-time RT-PCR assays specific for PSA and hK2 mRNA based on time-resolved fluorometric detection of lanthanide chelates. RESULTS: Reproducibility was best when large copy numbers (>5000 per milliliter blood) were analyzed. Addition of an exogenous target-mimicking internal standard had no significant effect on the reproducibility of the method, but increased the calculated copy numbers by an average of 2-fold. CONCLUSIONS: We developed an internally standardized, specific and reproducible real-time RT-PCR analysis method for PSA and hK2 mRNA in circulating cells in the bloodstream. Both PSA and hK2 assays are sufficiently sensitive to detect two LNCaP cells per milliliter whole blood.

Cancer-associated changes in the expression of TMPRSS2-ERG, PCA3, and SPINK1 in histologically benign tissue from cancerous vs noncancerous prostatectomy specimens.

OBJECTIVE: To investigate whether messenger ribonucleic acid (mRNA) expression of TMPRSS2-ERG fusion gene, a suggested prostate cancer (PCa) biomarker, was specific to cancerous lesions alone and to study the expression of SPINK1 and PCA3 mRNAs in the same cohort to also explore the proposed mutual exclusivity of TMPRSS2-ERG and SPINK1 expression. METHODS: Levels of 2 TMPRSS2-ERG transcripts, PCA3, and SPINK1 mRNAs were measured with highly standardized reverse transcription quantitative polymerase chain reaction assays in cystoprostatectomy specimens from 19 patients with invasive bladder cancer and 174 radical prostatectomy (RP) samples (88 histologically benign prostate [HBP] tissues and 86 from cancerous lesions) from 87 patients with clinically localized PCa. RESULTS: Expression of TMPRSS2-ERG transcripts was detected in 45 of 88 (51%) HBP tissues from RP specimens and more frequently (57 of 86, 66%) found in cancerous lesions. In contrast, TMPRSS2-ERG expression was detected in only 2 of 19 (11%) cystoprostatectomy specimens, both with incidental PCa foci elsewhere in the gland. Similar trends of changes in the expression of PCA3 and SPINK1 were present in HBP tissue from RP compared with cystoprostatectomy specimens. CONCLUSION: Although the expression of TMPRSS2-ERG, SPINK1, and PCA3 mRNA is higher or more frequently found in cancerous lesions, HBP tissues from patients with clinically localized PCa manifest molecular, mRNA level changes that are absent in cystoprostatectomy specimens lacking incidental PCa foci or infrequent in cystoprostatectomy specimens containing incidental PCa. If this finding is replicated, these molecular assays could be used to inform men with negative biopsy results about the likelihood of cancerous lesions in unsampled regions and hence the need for repeat biopsy.

Circulating biomarkers for prostate cancer.

Due to its significant applicability for early detection, risk prediction and follow-up evaluation, prostate specific antigen (PSA) has revolutionized our ability to treat prostate cancer patients. With the prevalent use of PSA for early detection during the last two decades, disease characteristics have been altered towards early detected, localized tumors with a high chance of cure following local therapy. This advantage faces the risk of overdetection and overtreatment. In addition, PSA lacks both, sensitivity and specificity to accurately detect patients at risk of prostate cancer. Therefore, novel biomarkers are urgently needed to improve identification of men at risk of having the disease and to predict the natural behaviour of the tumor. Recent advances in the evaluation of high-throughput technologies have led to the discovery of novel candidate markers for prostate cancer. This article will briefly discuss current PSA-based strategies and review several novel biomarkers for prostate cancer, detectable in blood.