Molecular staging of prostate cancer: comparison of nested reverse transcription polymerase chain reaction assay using prostate specific antigen versus prostate specific membrane antigen as primer

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.

Quantitative real-time reverse transcription: polymerase chain reaction of prostate-specific antigen (PSA) for detection of circulating prostatic cells in patients with clinically localized prostate cancer

OBJECTIVE

To evaluate the clinical utility of using the real-time reverse transcriptase-polymerase chain reaction (RT-PCR) to quantify prostate-specific antigen (PSA) mRNA in peripheral blood samples from patients with prostate cancer as a predictor of extraprostatic extension of the disease and to assess any correlations with known predictive markers of this condition.

METHODS

Immediately before radical prostatectomy, peripheral blood samples were taken from 42 men with clinically localized prostate cancer and analysed for PSA and 18S ribosomal (endogenous control) genes using real-time RT-PCR (with gene expression assays and the comparative CT-cycle threshold-method for quantifying). A total of 30 healthy male blood donors aged <50 y was taken as a control group. The relationships between PSA mRNA values, pathological and clinical features were analysed. PSA mRNA value, PSA level and biopsy Gleason score were then compared as predictors of extraprostatic extension.

RESULTS

PSA gene expression was 3.73 times significantly higher in patients with clinically localized prostate cancer than in healthy men (P<0.05). There was no relationship between PSA real-time RT-PCR values and pathological stage pT2 or pT3 (P=0.5), and no association between PSA mRNA value and serum PSA level (P=0.9) or the Gleason score of the preoperative biopsy (P=0.9).

CONCLUSION

There was no significant advantage in using the real-time RT-PCR assay of PSA mRNA before surgery to stage prostate cancer and to discriminate between organ-confined and extraprostatic extension.

The clinical utility of the prostate specific membrane antigen reverse-transcription/polymerase chain reaction to detect circulating prostate cells: an analysis in healthy men and women

OBJECTIVE

To evaluate the overall specificity of nested reverse transcriptase-polymerase chain reaction (RT-PCR) to detect prostate-specific membrane antigen (PSM) mRNA in peripheral blood samples of healthy donors.

SUBJECTS AND METHODS

Peripheral blood samples were taken from 60 healthy blood-donors (30 men and 30 women aged < 50 years) and analysed for PSM-mRNA using nested RT-PCR (in 'hot-start' conditions and confirmed using nested EcoRI restriction enzyme). Intron-spanning primer pairs specific for human PSM were deduced from the GenBank sequence (M99487) using gene software. The outer primer pair for PSM was: fwd: 1368 5'-TCACCGGGACTCATGGGTGT-3'; reverse: 1860 5'-GCCTGAAGCAATTCCAAGTCGG-3'. Inner primer pair for PSM was: fwd: 1480 5'-AAGGAAGGGTGGAGACCTAG-3'; reverse: 5-ACTGAACTCTGGGGAAGGAC-3'. The integrity of cDNAs was checked using primer pairs specific for the housekeeping gene beta-actin. The specificity and false-positive rate were calculated assuming that the underlying prostate cancer incidence was nil.

RESULTS

The first PCR was negative for all samples (100% specificity; 0% false-positive rate). The nested PCR detected 23 positive samples (23/60, 38%) with an overall specificity of 62% (false positive rate, 38%).

CONCLUSION

Nested RT-PCR of PSM-mRNA in peripheral blood is highly unspecific. Its clinical utility in the management of prostate cancer must be low. Further development is needed of quantitative RT-PCR, primers that identify prostatic PSM or another prostate-specific marker gene to differentiate PSM mRNA from circulating prostate cells and from non-prostatic tissues.

Reverse transcriptase-polymerase chain reaction for prostate-specific antigen in the molecular staging of pelvic surgical margins after radical prostatectomy

OBJECTIVES

To examine the application of reverse transcriptase-polymerase chain reaction (RT-PCR) to assist in prostate-specific antigen (PSA) detection in the surgical margins after radical prostatectomy (RP). The risk of local recurrence increases considerably in the presence of extracapsular tumor growth and/or positive surgical margins at RP. Although this makes it possible to identify patients with an increased risk of local recurrence, precise predictions cannot be made. A more precise assessment is desirable mainly for early planning of adjuvant therapy.

METHODS

Ninety-five patients with clinically organ-confined prostate cancer (CaP) underwent RP. After removing the gland, biopsies were obtained from four defined areas of the prostatic fossa and processed for RT-PCR for PSA detection. Sixteen patients with muscle-invasive bladder carcinoma who underwent radical cystoprostatectomy served as controls.

RESULTS

Thirty-two of 95 patients with CaP (35%) had at least one positive molecular margin indicating an expression for PSA; 19 of 48 (39%) of these had an organ-confined tumor stage according to conventional histology and 13 of 47 (28%) had tumor growth beyond the prostate. A statistically significant correlation between the frequency of positive molecular margins and clinical data was only observed in the group with disease greater than Stage pT2. All controls had negative molecular margins (P = 0.012).

CONCLUSIONS

On the basis of the results obtained, molecular diagnostic RT-PCR for PSA detection in the surgical margins after RP seems to be an interesting supplementary tool for monitoring the course and establishing the prognosis. Long-term follow-up of these patients is needed to demonstrate the clinical value of molecular diagnostics of surgical margins during RP.

The clinical relevance of molecular staging for melanoma

The presence of metastatic disease in the regional nodal basin is the most important prognostic indicator for patients with malignant melanoma. The metastatic status of the sentinel lymph node (SLN), defined as the first node in the basin to drain a primary tumor, has been shown to represent that of the entire basin. Since routine histologic examination of lymph nodes often underestimates the presence of micrometastatic disease, a more sensitive assay for detecting tumor cells is needed. We have previously shown that a molecular assay based on the reverse transcriptase polymerase chain reaction (RT-PCR) was able to define a population of patients at higher risk for both recurrence and death, compared with routine H&E histology. Recently, we have compared "molecular staging" of patients by RT-PCR with conventional S-100 immunohistochemistry (IHC) staining of the SLNs. In these studies, SLN specimens were bivaled, and half of each specimen was examined by routine histology, including both H&E and S-100 IHC. The other half of each specimen was analyzed by a nested RT-PCR assay. H&E histology alone detected metastatic disease in 36 of 233 (16%) patients tested. Serial sectioning and IHC detected micrometastatic disease in another 16 patients, thus increasing the proportion of patients with nodal disease to 22%. RT-PCR detected micrometastatic disease in 114 of 181 patients who were negative by conventional methods, further increasing the proportion of patients with evidence of nodal disease to 70% overall. The clinical significance of these findings is still uncertain. The value of additional therapy (including elective lymph node dissection and interferon therapy) for patients who are positive only by the molecular method is currently being investigated by the national multi-center Sunbelt Melanoma Trial.

Value of reverse transcription polymerase chain reaction assay in pathological stage T3N0 prostate cancer

BACKGROUND

We tested the ability of the nested reverse transcription polymerase chain reaction (RT-PCR) assay to detect signs of biochemical recurrence of prostate cancer in the lymph nodes and peripheral blood of patients with pT3N0 prostate cancer.

METHODS

Using lymph nodes and pre- and postoperative peripheral blood dissected from 30 patients with pT3N0 prostate cancer treated by radical prostatectomy, we used RT-PCR for prostate-specific membrane antigen (PSM) and serum prostate-specific antigen (PSA) to determine the presence of prostate cancer. Results of the nested RT-PCR assay were compared with pathological stages and biochemical recurrence.

RESULTS

Two of 13 patients with capsular penetration (15%), 6 of 10 patients with invasion of seminal vesicles (60%), and 3 of 7 patients with a positive surgical margin (43%) were RT-PCR-positive for PSM and/or PSA in the lymph nodes. Results of preoperative RT-PCRs of peripheral blood for PSM and for PSA significantly differed between positive and negative results of RT-PCR in lymph nodes (P < 0.001 and P < 0.001, respectively). Results of postoperative RT-PCRs of peripheral blood for PSM and for PSA also significantly different between positive and negative results of RT-PCR in lymph nodes (P = 0.011 and P = 0.001, respectively). Nine of 11 patients with positive nested RT-PCR for PSM and/or PSA in the lymph nodes (82%) experienced biochemical recurrence. Significant difference in Kaplan-Meier recurrence-free actuarial curves was noted between patients who nested positive and negative on RT-PCR in the lymph nodes, pre- and postoperative peripheral blood, biopsy and prostatectomy Gleason score, and preoperative PSA values. In multivariate analysis, biopsy and prostatectomy Gleason score (P = 0.026, P = 0.020, respectively), pre- and postoperative RT-PCR for PSM in peripheral blood (P = 0.030 and P = 0.040, respectively), and RT-PCR for PSM in lymph nodes (P = 0.035) were independent prognostic factors.

CONCLUSIONS

Nested RT-PCR assay of the lymph nodes or peripheral blood significantly predicted biochemical recurrence after surgery. It may help identify patients at risk for recurrence and progression of prostate cancer.

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.

Preoperative nested reverse transcription-polymerase chain reaction for prostate specific membrane antigen predicts biochemical recurrence after radical prostatectomy

OBJECTIVE

To assess the utility of the nested reverse transcription-polymerase chain reaction (RT-PCR) method for measuring prostate specific membrane antigen (PSM) and prostate specific antigen (PSA) in predicting serum PSA recurrence after radical prostatectomy.

PATIENTS AND METHODS

Nested RT-PCRs for PSM and PSA were used in 40 patients who subsequently underwent radical prostatectomy. The accuracy of the RT-PCR assays in predicting PSA failure was compared with those for the preoperative serum PSA level, Gleason score and final pathological staging. The patients were monitored using a PSA assay (Tandem-R, Hybritech, San Diego, CA) at 3 weeks after radical prostatectomy and every 2 months thereafter. Biochemical recurrence was defined as a serum PSA level of >/=0.4 ng/mL.

RESULTS

Statistical analysis indicated that the nested RT-PCR assay for PSM was the most accurate preoperative predictor of potential surgical failure (PCR-PSM, P<0.001; PCR-PSA, P=0.018; serum PSA level, P=0.149; Gleason score P=0.388, by Fisher's exact probability test). Biochemical recurrence was evaluated in relation to these methods during a mean (range) follow-up of 16.7 (6-35) months. Of the 40 patients, eight (20%, one with organ-confined cancer and seven with extraprostatic extension of cancer) developed biochemical recurrence. The Kaplan-Meier recurrence-free actuarial probability curves differed significantly between patients with positive and those with negative results for the preoperative nested RT-PCR for PSM (P<0.01, generalized Wilcoxon's test). The nested RT-PCR for PSA, preoperative serum PSA value and Gleason score were not significant predictors of biochemical recurrence (P=0.16, 0.12 and 0.24, respectively).

CONCLUSIONS

The nested RT-PCR for PSM was the best preoperative predictor of biochemical recurrence among the factors examined.