Application of immunomagnetic beads in combination with RT-PCR for the detection of circulating prostate cancer cells

Circulating Tumor DNA for Early Cancer Detection

BACKGROUND

Cancer cells release circulating tumor DNA (ctDNA) into the bloodstream, which can now be quantified and examined using novel high-throughput sequencing technologies. This has led to the emergence of the "liquid biopsy," which proposes to analyze this genetic material and extract information on a patient's cancer using a simple blood draw.

CONTENT

ctDNA has been detected in many advanced cancers. It has also been proven to be a highly sensitive indicator of relapse and prognosis. Sequencing the genetic material has also led to the discovery of mutations targetable by existing therapies. Although ctDNA screening is more expensive, it is showing promise against circulating tumor cells and traditional cancer biomarkers. ctDNA has also been detected in other bodily fluids, including cerebrospinal fluid, urine, saliva, and stool. The utility of ctDNA for early cancer detection is being studied. However, a blood test for cancer faces heavy obstacles, such as extremely low ctDNA concentrations in early-stage disease and benign mutations caused by clonal hematopoiesis, causing both sensitivity and specificity concerns. Nonetheless, companies and academic laboratories are highly active in developing such a test.

CONCLUSION

Currently, ctDNA is unlikely to perform at the high level of sensitivity and specificity required for early diagnosis and population screening. However, ctDNA in blood and other fluids has important clinical applications for cancer monitoring, prognosis, and selection of therapy that require further investigation.

Dissecting the Heterogeneity of Circulating Tumor Cells in Metastatic Breast Cancer: Going Far Beyond the Needle in the Haystack

Although the enumeration of circulating tumor cells (CTC) defined as expressing both epithelial cell adhesion molecule and cytokeratins (EpCAM⁺/CK⁺) can predict prognosis and response to therapy in metastatic breast, colon and prostate cancer, its clinical utility (i.e., the ability to improve patient outcome by guiding therapy) has not yet been proven in clinical trials. Therefore, scientists are now focusing on the molecular characterization of CTC as a way to explore its possible use as a “surrogate” of tumor tissues to non-invasively assess the genomic landscape of the cancer and its evolution during treatment. Additionally, evidences confirm the existence of CTC in epithelial-to-mesenchymal transition (EMT) characterized by a variable loss of epithelial markers. Since the EMT process can originate cells with enhanced invasiveness, stemness and drug-resistance, the enumeration and characterization of this population, perhaps the one truly responsible of tumor recurrence and progression, could be more clinically useful. For these reasons, several devices able to capture CTC independently from the expression of epithelial markers have been developed. In this review, we will describe the types of heterogeneity so far identified and the key role played by the epithelial-to-mesenchymal transition in driving CTC heterogeneity. The clinical relevance of detecting CTC-heterogeneity will be discussed as well.

Chemoaffinity capture of pre-targeted prostate cancer cells with magnetic beads

BACKGROUND

Prostate circulating tumor cells (PCTCs) in circulation are shed from either a primary tumor or metastases, which are directly responsible for most prostate cancer deaths. Quantifying exfoliated PCTCs may serve as an indicator for the clinical management of prostate cancer, isolating and removing of PCTCs could potentially reduce prostate cancer metastasis, and culturing and characterizing captured PCTCs could facilitate the development of personalized treatment options. Prostate-specific membrane antigen (PSMA) is an established biomarker for prostate cancer being strongly expressed on prostate tumor cells associated with high-grade primary, androgen independent, and metastatic tumors.

METHODS

Suspensions of PSMA+ (LNCaP) cells were pre-targeted with the irreversible PSMA inhibitor biotin-PEG(12)-CTT-54 to serve as a bait to capture PSMA+ cells using streptavidin-coated magnetic beads. Decreasing numbers of LNCaP cells were spiked into blood to determine the cell captured efficiency, recovery and viability.

RESULTS

High selectivity, recovery, and viability were achieved for the capture of PSMA+ cells in both model experiments with mixtures of LNCaP cells and WBCs as well as blood samples spiked with LNCaP cells. As low as 10 cells were captured from 1 ml of blood with nearly 90% viability. More importantly, captured cells could be subsequently propagated in vitro.

CONCLUSIONS

This methodology for the detection, isolation, and culture of PCTCs from peripheral blood can serve as an effective tool for the detection of metastatic prostate cancer, treatment monitoring, and the development of personalized therapy based on the responsiveness of PCTCs to chemotherapeutic strategies.

Detection of disseminated tumor cells in bone marrow of gastric cancer using magnetic activated cell sorting and fluorescent activated cell sorting

BACKGROUND AND AIM

Magnetic activated cell sorting (MACS) and fluorescent activated cell sorting (FACS) were employed to enrich and detect the gastric cancer cells from a cell line in a model system, and to enrich and detect disseminated tumor cells (DTCs) from bone marrow (BM) of patients with gastric cancer.

METHODS

Fifteen patients with benign gastric lesions and 35 patients with gastric cancer who received curative operations between December 2002 and June 2003 were selected. Mononuclear cells were separated from their BM. Cells from cell line OCUM-2M were seeded with 10-grade ratio into mononuclear cells from patients with benign gastric lesion. After labeling by MACS minibeads conjugated with cytokeratin (CK) 7/8 antibodies, anti-CK-fluorescein isothiocyanate (FITC), and anti-CD45-perdinin chlorophyll protein (PerCP), the samples were enriched twice using an MS+/RS+ positive separation column. The FACS analysis was conducted on these samples before and after MACS enrichment. The results were analyzed using clinopathological parameters.

RESULTS

Disseminated tumor cells were detected in the BM of 25 (71.43%) patients with gastric cancer. The frequencies of DTCs were 1.38 x 10(-8)-2.40 x 10(-5), 2.19 x 10(-7)-3.70 x 10(-5), 4.01 x 10(-6)-8.57 x 10(-5) in patients with well, moderately, and poorly differentiated carcinoma, respectively (P = 0.026). Disseminated tumor cells in BM had close correlation with tumor tumor-node-metastasis (TNM) stage (P = 0.034) and cancer-free survival (P = 0.035).

CONCLUSION

Disseminated tumor cells are very common in the BM of gastric cancer patients. Poor histological differentiation and more advanced TNM stage have more DTCs in the BM of gastric cancer patients. Patients with DTCs tend to have a poor prognosis.

Detection of circulating tumor cells in prostate cancer patients: methodological pitfalls and clinical relevance

Disseminated malignancy is the major cause of prostate cancer-related mortality. Circulating tumor cells (CTCs) are essential for the establishment of metastasis. Various contemporary and molecular methods using prostate-specific biomarkers have been applied to detect extraprostatic disease that is undetectable by conventional imaging techniques, assessing the risk for disease recurrence after therapy of curative intent. However, the clinical relevance of CTC detection is still controversial. We review current literature regarding molecular methods used for the detection of CTCs in the peripheral blood and bone marrow biopsies of patients with prostate cancer, and we discuss the methodological pitfalls that influence the clinical significance of molecular staging.

Application of immunomagnetic cell enrichment in combination with RT-PCR for the detection of rare circulating head and neck tumor cells in human peripheral blood

Detection of rare, circulating tumor cells (CTC's) in human peripheral blood is a potential indicator of prognosis and diagnosis in oncology. Typical methods to detect these CTC's are either by immunocytochemistry (ICCS) or RT-PCR. However without accurate, rapid, and reproducible enrichment processes, these detection techniques are labor intensive and/or unreliable. In this article, a repeatable enrichment process that included a flow-through immunomagnetic cell separation system, the quadrupole magnetic sorter (QMS) was optimized with the aid of a statistical analysis software package. The QMS was operated in a negative mode of operation by immunomagnetically targeting normal human peripheral blood lymphocytes (PBL) through the CD45 surface marker. Three head and neck squamous carcinoma cell lines (HNSCC), Detroit-562, SCC-4, and CAL-27, were used to determine the sensitivity of RT-PCR for the epidermal growth factor receptor (EGFR) in spiked PBL. The detection purity needed for detection was found to be one cell in 10(4), one cell in 10(3), and one cell in 10(5) for the Detroit-562, SCC-4, and CAL-27, respectively. The actual number of cancer cells needed for RT-PCR detection ranged from 30 to 1 cell. To mimic the potential concentration of rare CTC present in peripheral blood of cancer patients, the spiking concentration was chosen to be one cancer cell per 10(5) total leukocytes from healthy donors. Using a single step immunomagnetic labeling, the final, optimized enrichment process produced a 57.6 +/- 30.3-fold (n = 6) enrichment of the rare cancer cells with a final cancer cell recovery of (77.8 +/- 6.6)%.

Correlation between CD8+ T cells specific for prostate-specific antigen and level of disease in patients with prostate cancer

Modest work has been performed to improve the sensitivity of residual disease detection or investigate the contribution that the immune system makes in controlling metastatic tumor growth, in particular, the frequency and biological actions of peptide-specific CD8+ T lymphocytes in limiting metastatic disease and/or maintaining remission. Fifty-three peripheral blood samples from 32 prostate cancer (PC) patients were investigated for the presence of circulating prostate-specific antigen (PSA)-expressing cells (CPECs) using a highly sensitive and specific assay combining immunomagnetic epithelial cell enrichment with nested RT-PCR of PSA mRNA. Using HLA-A2 tetramer complexes, frequency of CD8+ T cells specific for PSA-derived peptides was determined. Additionally, serum concentrations of PSA and testosterone were measured. CPECs were detected in 26% of peripheral blood samples from PC patients. CD8+ T cells specific for PSA-derived peptides were detected at low frequency in HLA-A2-positive PC patients. The correlation between these PSA-specific CD8+ T cells and residual prostate tumor cells and clinical measures was investigated. Our data suggest that frequency of PSA-specific CD8+ T cells is correlated to CPECs, but not to serum PSA level.

Detection and isolation of circulating tumor cells in urologic cancers: a review

The American Cancer Society has estimated that in 2003, there will be approximately 239,600 new cases of urologic cancer diagnosed and 54,600 urologic cancer-related deaths in the United States. To date, the majority of research and therapy design have focused on the microenvironment of the primary tumor site, as well as the microenvironment of the metastatic or secondary (target) tumor site. Little attention has been placed on the interactions of the circulating tumor cells and the microenvironment of the circulation (i.e., the third microenvironment). The purpose of this review is to present the methods for the detection and isolation of circulating tumor cells and to discuss the importance of circulating tumor cells in the biology and treatment of urologic cancers.

Preliminary study of immunomagnetic quantification of circulating tumor cells in patients with advanced disease

OBJECTIVES

To enumerate the amount of circulating tumor cells (CTCs) in patients with advanced prostate cancer and to investigate the relationship between these numbers, prostate-specific antigen (PSA) and prostate-specific membrane antigen (PSM) expression, and clinical parameters.

METHODS

Whole blood was collected in proprietary CellSave tubes. Mononuclear cell fractions were isolated using epithelial cell antibody-coated magnetic nanoparticles. On one half of each immunomagnetically enriched cell fraction, automated fluorescent microscopy was used to identify the epithelial tumor cells. From the remainder of each sample, RNA extraction, cDNA synthesis, and polymerase chain reaction amplification of PSA and PSM were performed.

RESULTS

Eighty-four patients with advanced prostate cancer submitted 130 samples for analysis. Intact CTCs were identified in 62% of samples; 83.3% of CTC-positive and 0% of CTC-negative samples were reverse transcriptase-polymerase chain reaction positive for PSA and PSM (P = 0.001). A significant positive correlation was found between the CTC number and PSA (r = 0.49), alkaline phosphatase (r = 0.47), and lactate dehydrogenase (r = 0.55) levels, and a significant negative correlation with hemoglobin (r = -0.35). The initial Gleason grade, prior therapy, current therapy, and type of metastasis (bone, soft tissue) did not correlate significantly with the CTC number.

CONCLUSIONS

The presence of intact CTCs and the expression of PSA and PSM demonstrated robust agreement. The tumor cell numbers reflected current disease status and correlated significantly with the clinical disease indicators of PSA, hemoglobin, and liver function tests. These findings warrant further investigation of the diagnostic and prognostic value of enumerating intact CTCs.

Enrichment of rare cancer cells through depletion of normal cells using density and flow-through, immunomagnetic cell separation

OBJECTIVE

To develop a reliable technique to enrich for rare cells in blood suspensions using only negative selection steps including a flow-through immunomagnetic cell separations system and by optimizing variables normally encountered during such enrichment processes.

METHODS

A human breast cancer cell line was cultivated and spiked at a ratio of 1 cancer cell to 10(5) total leukocytes in buffy coat or 1 cancer cell to 10(8) total cells in whole blood samples. The final, optimized process consisted of: a red cell lysis step, immunomagnetically staining leukocytes with an anti-CD45 PE, anti- MACS sandwich, immunomagnetic sorting using a flow-through system (QMS), and a final cell analysis step using either an automated cell counter, filtration, and visual counting or a cytospin analysis.

RESULTS

The final, optimized process produced a final enrichment of the rare cancer cells of 5.17 log(10) and an average, final recovery of 46%. It should be noted that a negative depletion protocol was used (i.e., no labeling of the rare cancer cells was used).

CONCLUSIONS

To the authors' knowledge, no examples in the literature exist of a 5.17 log(10) enrichment of cancer cells in human blood using a negative depletion protocol. The closest example is a 4 log(10) enrichment in which two positive magnetic cell separation steps were used (none were used in this study). Ongoing studies are investigating further modifications of the precommercial, prototype flow-through immunmagnetic separation system to increase both the enrichment and recovery rate. However, even at current performance levels, the presented process could significantly improve visual and molecular analysis of rare cells in blood.

Changes in prostate-specific antigen (PSA) level correlate with growth inhibition of prostate cancer cells treated in vitro with a novel anticancer drug, irofulven

Irofulven (hydroxymethylacylfulvene, HMAF, MGI 114) is a novel agent with alkylating activity and a potent inducer of apoptosis. It is currently undergoing Phase II clinical trials for several tumor types, including hormone-refractory prostate cancer. Reduction of serum prostate-specific antigen (PSA) levels has been proposed as a generally useful endpoint for evaluating the antitumor efficacy of treatments for prostate cancer. However, the utility of PSA as a marker of tumor cell burden could be compromised, if drugs directly affected PSA secretion and/or expression. In these studies, we evaluated the effects of irofulven on PSA protein and mRNA levels during the course of treatment of prostate tumor cells in vitro. The rate of PSA secretion (normalized per equal cell number) by control and drug treated cells was similar, as determined by a solid phase, two-site immunoradiometric assay. Consistent with the lack of effect of irofulven on PSA protein level, the drug does not appear to affect the expression of PSA mRNA (on a per cell basis) as assessed by RT-PCR. Thus, changes in PSA secretion and expression appear to reflect irofulven-induced cell growth inhibition rather than reflecting a direct effect of the drug on PSA. These results suggest that PSA should be a reasonable marker of tumor burden in irofulven-treated prostate cancer patients.

Changes in circulating carcinoma cells in patients with metastatic prostate cancer correlate with disease status

OBJECTIVES

To investigate the diurnal variations in circulating tumor cells (CTCs) in metastatic carcinoma of the prostate (CAP) and to determine whether the change in CTCs correlated with disease progression.

METHODS

Samples were prepared by immunomagnetic selection of cells from 7 mL of blood targeting the epithelial cell adhesion molecule and differential fluorescent labeling of the collected cells using a nucleic acid dye, antibodies directed against the common leukocyte (CD45), and cytokeratin antigens. Events that stained with the nucleic acid dye and expressed cytokeratin but lacked CD45 were defined as CTCs by multiparameter flow cytometry.

RESULTS

Male controls (n = 22) exhibited 0.8 +/- 1.2 events per 7 mL blood compared with 5.9 +/- 4.7 in 10 samples from patients with localized CAP and 46.6 +/- 65.6 events in 10 samples from patients with metastatic CAP. Diurnal testing of 8 cases demonstrated stable levels of CTCs. Ten patients were serially analyzed during a 6-month period for serum prostate-specific antigen and CTCs. The correlation between the prostate-specific antigen level and CTC number was fair. Slow disease progression was found in 4 patients with low CTC numbers (3.0 +/- 3) but it was significantly higher than the control group (P <0.002). Rapid disease progression occurred in 6 patients who demonstrated high CTC numbers (68.5 +/- 71.9). Two patients received chemotherapy that caused substantial fluctuations in the CTCs with less pronounced changes in the prostate-specific antigen level.

CONCLUSIONS

We conclude that the level of CTCs can be quantified in the circulation of patients with metastatic CAP and that the change in CTCs correlates with disease progression with no diurnal variations.

Immunomagnetic cell enrichment detects more disseminated cancer cells than immunocytochemistry in vitro

PURPOSE

We describe a method to improve tumor cell detection compared to currently available immunocytochemical methods by using immunomagnetic cell enrichment.

MATERIALS AND METHODS

Two different methods of immunomagnetic cell enrichment using antibody coated magnetic beads were tested and compared with unenriched immunocytochemistry. One method was positive selection of epithelial cells from mononuclear cells with the antiepithelial antibody BER-EP4 and the other was depletion of mononuclear cells with the antileukocyte antibody CD45. Mononuclear cells were isolated from peripheral blood by density centrifugation and various numbers of tumor cells were added. The 5 different cell lines from urological malignancies used in the study were DU-145, RT-4, CAKI-2, KTCTL-2 and KTCTL-30. Following incubation of cell suspensions with the beads, cell separation was performed in a magnetic field. After centrifugation on glass slides immunocytochemical staining for cytokeratin was performed. A total of 112 experiments were completed and negative controls were obtained.

RESULTS

The number of tumor cells detected by positive selection and depletion was significantly higher than by immunocytochemistry (p <0.001). The median enrichment factor and tumor cell recovery rate for positive selection and depletion were 15.3 and 61.2%, and 13.0 and 57.3%, respectively (not significant). With less than 1 tumor cell suspended in 106 mononuclear cells, the probability of tumor cell detection was 23% for immunocytochemistry alone and 93.3% for both enrichment methods (p <0.01). No false-positive results were observed.

CONCLUSIONS

Compared to immunocytochemistry, immunomagnetic cell enrichment significantly improves the sensitivity of detection of epithelial cells added to mononuclear cells. Both methods of enrichment were equally effective and may be important for clinical practice in the future.

Optimization of the reverse transcriptase polymerase chain reaction for the detection of circulating prostate cells

The reverse transcriptase polymerase chain reaction (RT-PCR) is a sensitive technique that can detect prostate-specific messenger RNA in circulating blood. Many authors have studied the potential of RT-PCR as a staging technique in prostate cancer (PC). Clinical sensitivity and in some cases specificity has been disappointing. Few authors have been able to correlate RT-PCR result with patient stage. We have compared the results of using two different RT-PCR protocols with different sensitivities on blood samples from prostate cancer patients. An 80-amplification-cycle nested primer RT-PCR assay had a detection limit of 10 prostate cells and a 50-cycle RT-PCR could detect 20 cells in 5 ml blood. The 80-cycle assay detected prostate mRNA in four of 10 female samples, whereas the 50-cycle assay detected it in none. There was little difference in the assays' ability to detect prostate mRNA in advanced PC patients. The 50-cycle assay could differentiate between hormone-escaped, stable hormone-treated and untreated localized PC patients, whereas the 80-cycle assay could not. Each blood sample must be assayed several times with RT-PCR to avoid false-negative results and, if this is done, assay specificity can be increased with little effect on clinical sensitivity.

Pitfalls in the detection of disseminated non-hematological tumor cells

There is not yet a consensus on the reliability of the methods that should be used for the detection of rare disseminated tumor cells from non-hematological malignancies. In this review, we will discuss the advantage and drawbacks of the classical approach of immunocytochemistry and the molecular detection by reverse transcriptase polymerase chain reaction (RT-PCR). The interpretation of the biological significance of circulating tumor cells and the pitfalls of the detection techniques are the main causes of discrepancy between the conclusions of different tumor-cell detection (TCD) studies.

Detection of extraprostatic prostate cells utilizing reverse transcription-polymerase chain reaction

This article reviews the utility of reverse transcription-polymerase chain reaction (RT-PCR) in prostate cancer. RT-PCR aims to detect occult micrometastases in non-prostatic sites. Due to its exquisite analytical sensitivity, RT-PCR is able to amplify and detect even low-level, prostate-specific messages present at these extraprostatic sites. In recent years, a fair amount of data on the clinical utility of the technique had been reported. The target tissues under investigation are peripheral blood, bone marrow aspirate, and lymph nodes. Favorite markers of choice are prostate-specific antigen (PSA), prostate-specific membrane antigen (PSMA), and human glandular kallikrein-2 (hK2). False positives among negative controls are low. For the most part, RT-PCR is inadequate in detecting tumor cells in the peripheral blood from patients who are known to have metastatic prostate cancer. All studies showed that RT-PCR could detect PSA, PSMA or hK2 mRNAs in the circulation of patients who have organ-confined or extraprostatic disease. Most studies showed that RT-PCR utilizing current markers could not be used as a prospective test to diagnose prostate cancer. However, a few studies also showed that the detection rate could be predictive and sensitive enough to differentiate patients with organ-confined disease from those with extraprostatic disease. Data from PSA- or PSMA-RT-PCR using lymph nodes as the tissue source is more encouraging. RT-PCR was able to detect PSA and/or PSMA positive samples that have not been detected by conventional pathology.

Molecular detection of low-level disease in patients with cancer

The accurate detection of low-level disease in patients with cancer is essential to improve the staging of disease and consequently to define appropriate treatment strategies. Most methods currently used for staging are based on imaging studies and histological and immunocytochemical analysis of tissues such as bone marrow aspirates, or antibody assays for marker proteins secreted into the circulation. These methods have limited sensitivity. However, assays for nucleic acid-based markers may be valuable tools for the sensitive detection, assessment, and monitoring of disease status in asymptomatic cancer patients. Application of these methods may allow the early detection of cancer, when the tumour burden is smaller and the disease potentially more curable. The last decade has seen the application of polymerase chain reaction (PCR)-based methods to the detection of tumour in a wide variety of compartments, including peripheral blood, bone marrow, lymph nodes, urine, sputum, faeces, pancreatic juice, and more recently plasma. Molecular detection of disease by PCR has targeted DNA and RNA markers, including mutations, microsatellites, and tissue-specific gene expression. It is likely that these molecular methods will provide important clinical information, though their current clinical utility remains unclear. The current status of nucleic acid-based assays for the detection and assessment of disease status in the management of patients with solid tumours is reviewed.

Detection and clinical relevance of micrometastatic cancer cells

The failure to reduce mortality of epithelial cancer patients is probably a result of the early dissemination of cancer cells to secondary sites, which is usually missed by conventional diagnostic procedures used for tumor staging. Individual carcinoma cells present in regional lymph nodes, blood, or distant organs (eg, bone marrow) can be detected by sensitive immunologic or molecular methods. Because the goal of adjuvant therapy is the eradication of occult micrometastatic tumor cells before metastatic disease becomes clinically evident, the early detection of micrometastases could identify those patients who might benefit from adjuvant therapy. In addition, more sensitive methods for detecting such cells should increase knowledge about the biologic mechanisms of metastasis, which might improve the diagnosis and treatment of micrometastatic disease. In this article, the recent developments in sensitive assays used for the detection of individual micrometastatic cancer cells in patients with epithelial tumors are reviewed.

Detection of prostatic specific membrane antigen messenger RNA using immunobead reverse transcriptase polymerase chain reaction

The present study was performed to detect circulating prostatic carcinoma (PC) cells using a novel three-step immunobead reverse transcriptase (RT) polymerase chain reaction (PCR) assay for prostatic specific membrane antigen (PSMA) messenger RNA (mRNA). The sensitivity and specificity of this technique was assessed and the incidence of immunobead RT-PCR positivity correlated with progressive metastatic disease and serum prostatic specific antigen (PSA) levels. Fifty peripheral blood (PB) samples from 46 patients with PC were incubated with magnetic beads coated with Ber-EP4 antibody directed against the human epithelial antigen a membrane antigen widely expressed by epithelial cells. The epithelial cell-enriched magnetic fraction was then subjected to mRNA isolation using oligo-deoxythymidine (dT) magnetic beads. Nested RT-PCR for PSMA was performed on the mRNA oligo-dT complex and the identity of the RT-PCR products was confirmed by Southern blotting. Twenty-one PB samples from 8 control subjects without PC were also evaluated. Three-step immunobead PSMA RT-PCR was able to detect one PC cell per 1 mL of PB. The positivity rate of the RT-PCR assay was significantly higher (11 of 25; 44%) in patients with metastatic tumor than in patients with non-metastatic disease (1 of 21; 5%) (P = 0.003). In patients with metastatic PC, RT-PCR positivity was much higher in patients with progressive disease (10 of 13; 77%) than in patients with responding or stable disease (1 of 12; 8%) (P = 0.001). There was a statistically significant correlation between immunobead PSMA PCR positivity and high levels of serum PSA (P = 0.005). All control subjects without PC tested negative for PSMA PCR. The three-step immunobead RT-PCR for PSMA can detect circulating PC cells with high specificity and sensitivity. Preliminary data show a strong correlation between immunobead PCR positivity, the presence of progressive metastatic disease, and high levels of serum PSA.