The Use of Real-Time Reverse Transcription-PCR for Prostate-Specific Antigen mRNA to Discriminate between Blood Samples from Healthy Volunteers and from Patients with Metastatic Prostate Cancer

From Sampling to Sequencing: A Liquid Biopsy Pre-Analytic Workflow to Maximize Multi-Layer Genomic Information from a Single Tube

Simple Summary

Liquid biopsies seek to isolate tumor derived genetic material that circulates in blood plasma or cerebrospinal fluid. The less-invasive character of liquid biopsies combined with the option for serial analyses bears enormous potential for treatment monitoring or surveillance. We aimed to establish robust sampling protocols and pre-analytical workflows to allow for site independent multi-layer liquid biopsy testing. For an optimal usage of precious material, we explored sample stabilization in various conservation tubes and describe a protocol for the parallel isolation of cell-free DNA and RNA. Quantification and quality control steps were optimized for minimal sample use with both high sensitivity and reproducibility. We provide detailed step-by-step information on how to i) choose the best-suited protocol and ii) implement this in the liquid biopsy workflow. We believe that our study has potential to increase comparability of liquid biopsy approaches to bring these one step closer to routine clinical application.

Abstract

Liquid biopsies hold great promise for the management of cancer. Reliable liquid biopsy data depend on stable and reproducible pre-analytical protocols that comply with quality measures, irrespective of the sampling and processing site. We established a workflow for plasma preservation, followed by processing, cell-free nucleic acid isolation, quantification, and enrichment of potentially tumor-derived cell-free DNA and RNA. Employing the same input material for a direct comparison of different kits and protocols allowed us to formulate unbiased recommendations for sample collection, storage, and processing. The presented workflow integrates the stabilization in Norgen, PAX, or Streck tubes and subsequent parallel isolation of cell-free DNA and RNA with NucleoSnap and NucleoSpin. Qubit, Bioanalyzer, and TapeStation quantification and quality control steps were optimized for minimal sample use and high sensitivity and reproducibility. We show the efficiency of the proposed workflow by successful droplet digital PCR amplification of both cell-free DNA and RNA and by detection of tumor-specific alterations in low-coverage whole-genome sequencing and DNA methylation profiling of plasma-derived cell-free DNA. For the first time, we demonstrated successful parallel extraction of cell-free DNA and RNA from plasma samples. This workflow paves the road towards multi-layer genomic analysis from one single liquid biopsy sample.

Prostate-specific markers to identify rare prostate cancer cells in liquid biopsies

Despite improvements in early detection and advances in treatment, patients with prostate cancer continue to die from their disease. Minimal residual disease after primary definitive treatment can lead to relapse and distant metastases, and increasing evidence suggests that circulating tumour cells (CTCs) and bone marrow-derived disseminated tumour cells (BM-DTCs) can offer clinically relevant biological insights into prostate cancer dissemination and metastasis. Using epithelial markers to accurately detect CTCs and BM-DTCs is associated with difficulties, and prostate-specific markers are needed for the detection of these cells using rare cell assays. Putative prostate-specific markers have been identified, and an optimized strategy for staining rare cancer cells from liquid biopsies using these markers is required. The ideal prostate-specific marker will be expressed on every CTC or BM-DTC throughout disease progression (giving high sensitivity) and will not be expressed on non-prostate-cancer cells in the sample (giving high specificity). Some markers might not be specific enough to the prostate to be used as individual markers of prostate cancer cells, whereas others could be truly prostate-specific and would make ideal markers for use in rare cell assays. The goal of future studies is to use sensitive and specific prostate markers to consistently and reliably identify rare cancer cells.

Consensus reference gene(s) for gene expression studies in human cancers: end of the tunnel visible?

BACKGROUND

Gene expression studies are increasingly used to provide valuable information on the diagnosis and prognosis of human cancers. Also, for in vitro and in vivo experimental cancer models gene expression studies are widely used. The complex algorithms of differential gene expression analyses require normalization of data against a reference or normalizer gene, or a set of such genes. For this purpose, mostly invariant housekeeping genes are used. Unfortunately, however, there are no consensus (housekeeping) genes that serve as reference or normalizer for different human cancers. In fact, scientists have employed a wide range of reference genes across different types of cancer for normalization of gene expression data. As a consequence, comparisons of these data and/or data harmonizations are difficult to perform and challenging. In addition, an inadequate choice for a reference gene may obscure genuine changes and/or result in erroneous gene expression data comparisons.

METHODS

In our effort to highlight the importance of selecting the most appropriate reference gene(s), we have screened the literature for gene expression studies published since the turn of the century on thirteen of the most prevalent human cancers worldwide.

CONCLUSIONS

Based on the analysis of the data at hand, we firstly recommend that in each study the suitability of candidate reference gene(s) should carefully be evaluated in order to yield reliable differential gene expression data. Secondly, we recommend that a combination of PPIA and either GAPDH, ACTB, HPRT and TBP, or appropriate combinations of two or three of these genes, should be employed in future studies, to ensure that results from different studies on different human cancers can be harmonized. This approach will ultimately increase the depth of our understanding of gene expression signatures across human cancers.

Anti-tumor effects of suberoylanilide hydroxamic acid on Epstein-Barr virus-associated T cell and natural killer cell lymphoma

The ubiquitous Epstein–Barr virus (EBV) infects not only B cells but also T cells and natural killer (NK) cells and is associated with various lymphoid malignancies. Recent studies have reported that histone deacetylase (HDAC) inhibitors exert anticancer effects against various tumor cells. In the present study, we have evaluated both the in vitro and in vivo effects of suberoylanilide hydroxamic acid (SAHA), an HDAC inhibitor, on EBV-positive and EBV-negative T and NK lymphoma cells. Several EBV-positive and EBV-negative T and NK cell lines were treated with various concentrations of SAHA. SAHA suppressed the proliferation of T and NK cell lines, although no significant difference was observed between EBV-positive and EBV-negative cell lines. SAHA induced apoptosis and/or cell cycle arrest in several T and NK cell lines. In addition, SAHA increased the expression of EBV-lytic genes and decreased the expression of EBV-latent genes. Next, EBV-positive NK cell lymphoma cells were subcutaneously inoculated into severely immunodeficient NOD/Shi-scid/IL-2Rγnull mice, and then SAHA was administered intraperitoneally. SAHA inhibited tumor progression and metastasis in the murine xenograft model. SAHA displayed a marked suppressive effect against EBV-associated T and NK cell lymphomas through either induction of apoptosis or cell cycle arrest, and may represent an alternative treatment option.

Antitumor activities of valproic acid on Epstein-Barr virus-associated T and natural killer lymphoma cells

Epstein-Barr virus (EBV), which infects B cells, T cells, and natural killer (NK) cells, is associated with multiple lymphoid malignancies. Recently, histone deacetylase (HDAC) inhibitors have been reported to have anticancer effects against various tumor cells. In the present study, we evaluated the killing effect of valproic acid (VPA), which acts as an HDAC inhibitor, on EBV-positive and -negative T and NK lymphoma cells. Treatment of multiple T and NK cell lines (SNT13, SNT16, Jurkat, SNK6, KAI3 and KHYG1) with 0.1-5 mM of VPA inhibited HDAC, increased acetylated histone levels and reduced cell viability. No significant differences were seen between EBV-positive and -negative cell lines. Although VPA induced apoptosis in some T and NK cell lines (SNT16, Jurkat and KHYG1) and cell cycle arrest, it did not induce lytic infection in EBV-positive T or NK cell lines. Because the killing effect of VPA was modest (1 mM VPA reduced cell viability by between 22% and 56%), we tested the effects of the combination of 1 mM of VPA and 0.01 μM of the proteasome inhibitor bortezomib. The combined treated of cells with VPA and bortezomib had an additive killing effect. Finally, we administered VPA to peripheral blood mononuclear cells from three patients with EBV-associated T or NK lymphoproliferative diseases. In these studies, VPA had a greater killing effect against EBV-infected cells than uninfected cells, and the effect was increased when VPA was combined with bortezomib. These results indicate that VPA has antitumor effects on T and NK lymphoma cells and that VPA and bortezomib may have synergistic effects, irrespective of the presence of EBV.

Utility of urothelial mRNA markers in blood for staging and monitoring bladder cancer

OBJECTIVE

To test the efficiency of 6 mRNA bladder markers in staging urothelial cell carcinoma (UCC) and monitoring UCC dissemination from blood samples.

METHODS

From 2002 to 2009, 347 blood samples were collected from 150 patients with UCC and 29 healthy controls. Sequential blood sampling was performed in patients undergoing cystectomy at surgery and 6, 12, 18, and 24 months postoperatively. The median follow-up was 33 months. The presence of KRT20, FXYD3, C10orf116, UPK2, AGR2, and KRT19 markers in blood was evaluated in all patients and controls by measuring the gene expression using preamplified cDNA and reverse transcriptase quantitative polymerase chain reaction. Gene expression data were correlated with the tumor risk, follow-up, and outcomes data.

RESULTS

Expression of C10orf116 and KRT19 genes differed between patients and controls (P<.001). KRT20, C10orf116, and AGR2 differentiated between low- and high-risk nonmuscle-invasive bladder cancer (P=.001, P=.011, and P=.001, respectively). FXYD3 differentiated between patients with high-risk nonmuscle-invasive bladder cancer and those with muscle-invasive bladder cancer (P=.009). In contrast, the 6 markers showed no differences in gene expression between metastatic and patients without metastases who had not undergone cystectomy (P=NS). None of the markers were significantly increased in the metastatic patients at 6, 12, 18, or 24 months after surgery.

CONCLUSION

The gene expression of bladder-specific mRNA markers in blood was different among the various tumor risk groups of patients with UCC. However, this gene expression analysis is not suitable for predicting metastases or monitoring UCC hematogenous dissemination in patients who have undergone cystectomy.

Recovering circulating extracellular or cell-free RNA from bodily fluids

The presence of extracellular circulating or cell-free RNA in biological fluids is becoming a promising diagnostic tool for non invasive and cost effective cancer detection. Extracellular RNA or miRNA as biological marker could be used either for the early detection and diagnosis of the disease or as a marker of recurrence patterns and surveillance. In this review article, we refer to the origin of the circulating extracellular RNA, we summarise the data on the biological fluids (serum/plasma, saliva, urine, cerebrospinal fluid and bronchial lavage fluid) of patients suffering from various types of malignancies reported to contain a substantial amount of circulating extracellular (or cell-free) RNAs and we discuss the appropriate reagents and methodologies needed to be employed in order to obtain RNA material of high quality and integrity for the majority of the experimental methods used in RNA expression analysis. Furthermore, we discuss the advantages and disadvantages of the RT-PCR or microarray methodology which are the methods more often employed in procedures of extracellular RNA analysis.

Bortezomib induces apoptosis in T lymphoma cells and natural killer lymphoma cells independent of Epstein-Barr virus infection

Epstein-Barr virus (EBV), which infects not only B cells, but also T cells and natural killer (NK) cells, is associated with multiple lymphoid malignancies. Recently, the proteasome inhibitor bortezomib was reported to induce apoptosis of EBV-transformed B cells. We evaluated the killing effect of this proteasome inhibitor on EBV-associated T lymphoma cells and NK lymphoma cells. First, we found that bortezomib treatment decreased the viability of multiple T and NK cell lines. No significant difference was observed between EBV-positive and EBV-negative cell lines. The decreased viability in response to bortezomib treatment was abrogated by a pan-caspase inhibitor. The induction of apoptosis was confirmed by flow cytometric assessment of annexin V staining. Additionally, cleavage of caspases and polyadenosine diphosphate-ribose polymerase, increased expression of phosphorylated IκB, and decreased expression of inhibitor of apoptotic proteins were detected by immunoblotting in bortezomib-treated cell lines. We found that bortezomib induced lytic infection in EBV-positive T cell lines, although the existence of EBV did not modulate the killing effect of bortezomib. Finally, we administered bortezomib to peripheral blood mononuclear cells from five patients with EBV-associated lymphoproliferative diseases. Bortezomib had a greater killing effect on EBV-infected cells. These results indicate that bortezomib killed T or NK lymphoma cells by inducing apoptosis, regardless of the presence or absence of EBV.

Quantitative analysis of Epstein-Barr virus (EBV)-related gene expression in patients with chronic active EBV infection

Chronic active Epstein-Barr virus (CAEBV) infection is a systemic Epstein-Barr virus (EBV)-positive lymphoproliferative disorder characterized by persistent or recurrent infectious mononucleosis-like symptoms in patients with no known immunodeficiency. The detailed pathogenesis of the disease is unknown and no standard treatment regimen has been developed. EBV gene expression was analysed in peripheral blood samples collected from 24 patients with CAEBV infection. The expression levels of six latent and two lytic EBV genes were quantified by real-time RT-PCR. EBV-encoded small RNA 1 and BamHI-A rightward transcripts were abundantly detected in all patients, and latent membrane protein (LMP) 2 was observed in most patients. EBV nuclear antigen (EBNA) 1 and LMP1 were detected less frequently and were expressed at lower levels. EBNA2 and the two lytic genes were not detected in any of the patients. The pattern of latent gene expression was determined to be latency type II. EBNA1 was detected more frequently and at higher levels in the clinically active patients. Quantifying EBV gene expression is useful in clarifying the pathogenesis of CAEBV infection and may provide information regarding a patient's disease prognosis, as well as possible therapeutic interventions.

Regulation of androgen receptor transcriptional activity and specificity by RNF6-induced ubiquitination

The androgen receptor (AR) plays a critical role in prostate cancer. We have identified a ubiquitin E3 ligase, RNF6, as an AR-associated protein in a proteomic screen. RNF6 induces AR ubiquitination and promotes AR transcriptional activity. Specific knockdown of RNF6 or mutation of RNF6-induced ubiquitination acceptor sites on AR selectively alters expression of a subset of AR target genes and diminishes recruitment of AR and its coactivators to androgen-responsive elements present in the regulatory region of these genes. Furthermore, RNF6 is overexpressed in hormone-refractory human prostate cancer tissues and required for prostate cancer cell growth under androgen-depleted conditions. Our data suggest that RNF6-induced ubiquitination may regulate AR transcriptional activity and specificity through modulating cofactor recruitment.

One-step multiplex real-time PCR assay to analyse the latency patterns of Epstein-Barr virus infection

Epstein-Barr virus (EBV) establishes a latent infection with three types of viral gene expression. These latency types can be distinguished by the expression patterns of EBV nuclear antigen (EBNA)1, EBNA2, latent membrane protein (LMP)1, and LMP2. The EBV lytic cycle is initiated by the transcription of the EBV immediate early BZLF1 gene, which can be used to distinguish between a latent and a lytic infection. In this study, a one-step multiplex real-time PCR assay was developed to quantify the EBNA1, EBNA2, LMP1, LMP2, and BZLF1 expression levels simultaneously by relative quantification. To validate this assay, the quantitation of viral gene transcription was performed in EBV-positive B, T, and natural killer cell lines. Because of its rapidity, sensitivity, and specificity, this new assay can be used for quantitative analyses of the latency patterns of EBV infection and the switch from latency to lytic viral replication.

Circulating tumor cells in perioperative esophageal cancer patients: quantitative assay system and potential clinical utility

PURPOSE

To establish a quantitative system for evaluating the role of circulating tumor cells (CTC) in peripheral blood samples in patients who undergo surgery for treatment of esophageal cancer.

EXPERIMENTAL DESIGN

One hundred fifty-five peripheral blood samples from 53 esophageal cancer patients were collected before surgery (B-1), immediately after surgery (B0), and on the 3rd day postoperatively (B+3). Eighty-nine samples from 22 benign patients who underwent thoracotomy and 30 healthy volunteers were obtained as controls. A real-time reverse transcription-PCR quantitative analysis system based on carcinoembryonic antigen (CEA) mRNA gene expression was designed for detection of CTC.

RESULTS

This developed system can detect CEA mRNA-positive cells down to 3 cells per milliliter of peripheral blood. The cells in negative control groups were lower than the detection limit. The medians of 188 [95% confidence interval (95% CI), 155-498], 1513 (95% CI, 660-7,974) and 707 (95% CI, 737-3,005) CEA mRNA-positive cells per mL with the CEA-positive rates of 28.3%, 60.4%, and 42.9% in B-1, B0, and B+3 peripheral blood samples were obtained, respectively. There was statistically significant difference between B-1 and B0 (P=0.0001) and between B-1 and B+3 (P=0.0209). Fifty percent of patients with R>0.4 showed metastasis in 1 year after surgery, whereas the probability was only 14.3% for patients with R<0.4 (where R is CTC ratio of B+3 to B0, P=0.043).

CONCLUSIONS

Esophageal cancer operation results in tumor cells dissemination and significant increase of CTC in peripheral blood, which is related to the developed metastasis. CTC are helpful for evaluating micrometastasis and have the potential for predicting recurrence in esophageal cancer.

Evaluation and significance of circulating epithelial cells in patients with hormone-refractory prostate cancer

OBJECTIVE

To determine the feasibility of using flow cytometry fluorescence-activated cell sorting (FACS) analysis for detecting circulating epithelial cells (CECs) in patients with hormone-refractory prostate cancer (HRPC), and to determine whether CECs can be used to predict survival in these patients.

PATIENTS AND METHODS

Several prognostic models that include routinely used clinical and laboratory variables for predicting survival in men with HRPC have been reported; the presence of CECs measured by reverse transcriptase-polymerase chain reaction for prostate-specific antigen (PSA) in patients with HRPC is an independent prognostic factor for survival. CECs detected by FACS analysis correlate with advanced stage and poor survival outcome. A retrospective study was conducted to assess the presence of CECs by FACS analysis in metastatic HRPC patients initiating systemic chemotherapy with a taxane-based regimen. The association between clinical variables previously described and the presence of CECs along with the effect of the magnitude of CECs on survival was calculated, in 41 patients with HRPC, all of whom had peripheral blood collected for FACS analysis.

RESULTS

Except for four patients, all those with metastatic HRPC had detectable CECs. Among these patients, the number of CECs/mL was correlated with age, serum PSA level and serum alkaline phosphatase (ALP). Higher serum levels of PSA and ALP predicted a poor survival outcome. Similarly, patients with < or =1.8 CECs/mL had a significantly longer survival than those with more CECs/mL (P = 0.02). With a median follow-up of 15.4 months, the median overall survival for all patients was 18.4 months.

CONCLUSIONS

The presence of more CECs in patients with metastatic HRPC was associated with a poorer survival outcome; levels of > or =1.8 CECs/mL were associated with a shorter survival in patients with metastatic HRPC.

Molecular biomarkers for cancer detection in blood and bodily fluids

Cancer is a major and increasing public health problem worldwide. Traditionally, the diagnosis and staging of cancer, as well as the evaluation of response to therapy have been primarily based on morphology, with relatively few cancer biomarkers currently in use. Conventional biomarker studies have been focused on single genes or discrete pathways, but this approach has had limited success because of the complex and heterogeneous nature of many cancers. The completion of the human genome project and the development of new technologies have greatly facilitated the identification of biomarkers for assessment of cancer risk, early detection of primary cancers, monitoring cancer treatment, and detection of recurrence. This article reviews the various approaches used for development of such markers and describes markers of potential clinical interest in major types of cancer. Finally, we discuss the reasons why so few cancer biomarkers are currently available for clinical use.

Identification of prostate cancer mRNA markers by averaged differential expression and their detection in biopsies, blood, and urine

The advent of serum prostate-specific antigen (PSA) as a biomarker has enabled early detection of prostate cancer and, hence, improved clinical outcome. However, a low PSA is not a guarantee of disease-free status, and an elevated PSA is frequently associated with a negative biopsy. Therefore, our goal is to identify molecular markers that can detect prostate cancer with greater specificity in body fluids such as urine or blood. We used the RT-PCR differential display method to first identify mRNA transcripts differentially expressed in tumor vs. patient-matched nontumor prostate tissue. This analysis led to the identification of 44 mRNA transcripts that were expressed differentially in some but not all tumor specimens examined. To identify mRNA transcripts that are differentially expressed in most tumor specimens, we turned to differential display of pooled tissue samples, a technique we name averaged differential expression (ADE). We performed differential display of mRNA from patient-matched nontumor vs. tumor tissue, each pooled from 10 patients with various Gleason scores. Differentially expressed mRNA transcripts identified by ADE were fewer in number, but were expressed in a greater percentage of tumors (>75%) than those identified by differential display of mRNA from individual patient samples. Differential expression of these mRNA transcripts was also detected by RT-PCR in mRNA isolated from urine and blood samples of prostate cancer patients. Our findings demonstrate the principle that specific cDNA probes of frequently differentially expressed mRNA transcripts identified by ADE can be used for the detection of prostate cancer in urine and blood samples.

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.

Detection of Occult Lymph Node Metastases in Locally Advanced Node-Negative Prostate Cancer

Purpose

The purpose of this study was to determine the incidence and clinical significance of occult metastases in the lymph nodes of patients with prostate cancer originally considered node negative by routine histologic evaluation.

Methods

Two hundred seventy four patients with pT3 prostate carcinoma treated by radical prostatectomy and bilateral lymph node dissection were included in this study. One hundred eighty patients were staged node negative (N0), while 94 patients were lymph node positive (N+), based on routine histologic evaluation. All lymph nodes from the 180 N0 patients were evaluated for occult metastases by immunohistochemistry using antibodies to cytokeratins and, if positive, prostate-specific antigen. Recurrence and overall survival were compared among patients with occult tumor cells (OLN+), with patients whose lymph nodes remained negative (OLN−), and with the 94 N+ patients.

Results

A total of 3,914 lymph nodes were evaluated from 180 N0 patients (average, 21.7 lymph nodes per patient). Occult tumor cells were found in 24 of 180 patients (13.3%). The presence of OLN+ was significantly associated with increased recurrence and decreased survival compared with OLN− patients (P < .001 and P = .019, respectively; relative risk of recurrence, 2.27; relative risk of death 2.07, respectively). The presence of occult lymph node metastases was an independent predictor of recurrence and death in a multivariable analysis. The outcome for patients with OLN+ disease was similar to that for patients with N+ disease.

Conclusion

The detection of occult lymph node metastases in patients with pT3N0 prostate cancer identifies those with significantly increased risk of prostate cancer recurrence and death.

Quantitative analysis of MC1R gene expression in human skin cell cultures

To address the issue of melanocortin-1 receptor (MC1R) expression in non-melanocytic cells, we have quantitatively evaluated the relative expression levels of both MC1R mRNA and protein in a subset of different cell types. Using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) at high cycle numbers, we detected MC1R mRNA in all cell types examined, including human embryonic kidney-293 (HEK 293) cells, a cell type widely used as a negative control in melanocortin expression studies. Quantitative real-time PCR revealed the highest levels of MC1R transcripts were in melanocytic cells, whereas the keratinocyte and fibroblast cell cultures examined had only a low level of expression, similar to that of HEK 293 cells. Antibody mediated detection of MC1R protein in membrane extracts demonstrated exogenous receptor in MC1R transfected cell lines, as well as endogenous MC1R in melanoma cells. However, radioligand binding procedures were required to detect MC1R protein of normal human melanocytes and no surface expression of MC1R was detected in any of the non-melanocytic cells examined. This was consistent with their low level of mRNA, and suggests that, if present, the levels of surface receptor are significantly lower than that in melanocytes. The capacity of such limited levels of MC1R protein to influence non-melanocytic skin cell biology would likely be severely compromised. Indeed, the MC1R agonist [NIe(4), D-Phe(7)] alpha-melanocyte stimulating hormone (NDP-MSH) was unable to elevate intracellular cyclic adenosine monophosphate (cAMP) levels in the keratinocyte and fibroblast cells examined, whereas a robust increase was elicited in melanocytes. Although there are a variety of cell types with detectable MC1R mRNA, the expression of physiologically significant levels of the receptor may be more restricted than the current literature indicates, and within epidermal tissue may be limited to the melanocyte.

Critical evaluation of real-time reverse transcriptase-polymerase chain reaction for the quantitative detection of cytokeratin 20 mRNA in colorectal cancer patients

We evaluated the usefulness of cytokeratin 20 (CK20) mRNA expression in the quantitative detection of circulating tumor cells in the blood of patients with colorectal cancer (CRC). Blood samples from healthy volunteers (HVs; n = 37), patients with localized (n = 42) and metastatic colorectal cancer (n = 40), and patients with chronic inflammatory bowel disease (CID; n = 15) were examined. After immunomagnetic enrichment using microbeads against human epithelial antigen, total RNA was extracted, reverse transcribed, and analyzed by real-time reverse transcriptase-polymerase chain reaction using the LightCycler instrument. CK20 expression in peripheral blood was found in 46 of 82 (56%) patients with CRC, 8 of 37 (22%) HVs, and 9 of 15 (60%) patients with CID. Levels of CK20 mRNA were significantly higher in blood samples from CRC patients (median 681) than in blood samples from HVs (median 0) (P = 0.001), whereas no difference could be detected between patients with CRC and CID. Although the present technique could not distinguish CRC from CID, the method warrants further efforts to improve sample preparation and tumor cell enrichment, which may render real-time CK20 reverse transcriptase-polymerase chain reaction a feasible technique in identifying circulating tumor cells in peripheral blood of cancer patients.

Circulating tumor cells: the 'leukemic phase' of solid cancers

It is well known that malignant cells circulate in the bloodstream of patients with solid tumors. However, the biological significance of circulating tumor cells (CTCs) and the clinical relevance of their detection are still debated. Besides technical issues regarding CTC-detection methods, discontinuous shedding of CTCs from established cancer deposits, genomic instability and metastatic inefficiency might underlie the conflicting results currently available. Nevertheless, technological advances and recent clinical findings are prompting researchers to dissect CTC biology further. Here, we review these recent findings, and discuss the prospects for the identification and molecular characterization of the CTC subset that is responsible for metastasis development. This would provide a formidable tool for prognosis evaluation, anticancer-drug development and, ultimately, cancer-therapy personalization.