Prognostic Value of EMT-Circulating Tumor Cells in Metastatic Breast Cancer Patients Undergoing High-Dose Chemotherapy with Autologous Hematopoietic Stem Cell Transplantation

Gene expression profiling of circulating tumor cells captured by MicroCavity Array is superior to enumeration in demonstrating therapy response in patients with newly diagnosed advanced and locally advanced non-small cell lung cancer

Background

Circulating tumor cells (CTCs) are a promising non-invasive tool for monitoring therapy response. The only Food and Drug Administration (FDA)-approved test is limited to enumeration of epithelial CTC without further characterization and is not approved for the management of non-small cell lung cancer (NSCLC). Here we use a MicroCavity Array (MCA) system to capture CTC agnostic of epithelial markers for further molecular testing in NSCLC.

Methods

CTCs were enumerated by fluorescent microscopy as longitudinal sampling throughout disease management from 213 NSCLC patients. CTC-enriched samples from a subset of 127 patients were interrogated for gene expression by reverse transcription polymerase chain reaction (RT-PCR) using a customized pre-selected panel of 20 genes.

Results

At least 1 CTC was detected by enumeration in 53.8% of samples. Most patients had fewer than 5 CTCs (91%) and the highest observed count was 35 CTCs. Enumeration of single CTCs was not prognostic, although detection of CTC clusters at any time point was associated with increased risk of progression [hazard ratio (HR) 3.00, 95% confidence interval (CI): 1.1-8.2, P=0.0318]. In contrast, 124 (97.6%) patients with samples interrogated for gene expression had at least 1 gene detectable in at least 1 sample, and 101 (79.5%) had at least one elevated epithelial gene in at least one timepoint. High expression of BCL2, CD274 [programmed death-ligand 1 (PD-L1)], CDH1, EPCAM, FGFR1, FN1, KRT18, MET and MUC1 were associated with poor prognosis. Patients with CTCs positive for at least 3 epithelial genes at baseline all progressed within 10 months (HR 8.2, P<0.001, 95% CI: 3.2-21.1). BCL2, CD274 (PD-L1), EPCAM and MUC1 remained significant independent prognostic factors in multivariate, time-dependent analyses of progression and death.

Conclusions

The selective profile of CTC genes and identification of CTC clusters better correlated with prognosis than enumeration of enriched CTC in NSCLC patients in this study.

Crucial roles of circulating tumor cells in the metastatic cascade and tumor immune escape: biology and clinical translation

Cancer-related deaths are mainly caused by metastatic spread of tumor cells from the primary lesion to distant sites via the blood circulation. Understanding the mechanisms of blood-borne tumor cell dissemination by the detection and molecular characterization of circulating tumor cells (CTCs) in the blood of patients with cancer has opened a new avenue in cancer research. Recent technical advances have enabled a comprehensive analysis of the CTCs at the genome, transcriptome and protein level as well as first functional studies using patient-derived CTC cell lines. In this review, we describe and discuss how research on CTCs has yielded important insights into the biology of cancer metastasis and the response of patients with cancer to therapies directed against metastatic cells. Future investigations will show whether CTCs leaving their primary site are more vulnerable to attacks by immune effector cells and whether cancer cell dissemination might be the 'Achilles heel' of metastatic progression. Here, we focus on the lessons learned from CTC research on the biology of cancer metastasis in patients with particular emphasis on the interactions of CTCs with the immune system. Moreover, we describe and discuss briefly the potential and challenges for implementing CTCs into clinical decision-making including detection of minimal residual disease, monitoring efficacies of systemic therapies and identification of therapeutic targets and resistance mechanisms.

Prognostic value of epithelial–mesenchymal transition circulating tumor cells in female breast cancer: A meta-analysis

Background

Epithelial–mesenchymal transition (EMT) conferred metastatic properties on circulating tumor cells (CTCs) and was considered to be correlated with bad survival outcomes in patients with breast cancer. However, different studies have reported controversial results regarding the relationship between CTCs that have undergone EMT (EMT-CTCs) and prognosis of breast cancer. Therefore, this meta-analysis aimed to investigate the prognostic role of EMT-CTCs in patients with breast cancer.

Methods

In total, 842 patients from nine studies that were screened from Web of Science, Embase, and PubMed were included. The hazard ratio (HR) and 95% confidence interval (CI) for progression-free survival (PFS) and overall survival (OS) were extracted or estimated by the Kaplan–Meier survival curve for the meta-analysis. Sensitivity analysis was performed to characterize heterogeneity among the trials. Meanwhile, subgroup analysis was performed to present the effects of cancer stage, identification method, sampling volume, and region on the prognostic value of EMT-CTCs.

Results

The pooled HRs for PFS were 1.97 (univariate: 95% CI, 1.19–3.24; p = 0.008) and 2.23 (multivariate: 95% CI, 1.29–3.86; p = 0.004). The pooled HRs for OS were 2.03 (univariate: 95% CI, 1.07–3.84; p = 0.029) and 1.70 (multivariate: 95% CI, 1.14–2.52; p = 0.009). Subgroup analysis showed that EMT-CTCs were associated with PFS in the primary breast cancer group (pooled HR = 2.58, 95% CI, 1.66–4.00, p &lt; 0.001), the polymerase chain reaction (PCR) group (pooled HR = 2.69, 95% CI, 1.66–4.35, p &lt; 0.001), the sampling volume of the &gt;7.5-ml group (pooled HR = 1.93, 95% CI, 1.36–2.73, p &lt; 0.001), and the Asia group (pooled HR = 1.92, 95% CI, 1.13–3.29, p = 0.017) and with OS in the primary breast cancer group (pooled HR = 3.59, 95% CI, 1.62–7.95; p = 0.002).

Conclusion

The meta-analysis showed that EMT-CTCs were associated with poorer survival outcomes in patients with breast cancer. More accurate methods and designed clinical trials with unified standards are essential to establish the real role of EMT-CTCs in disease progression in women with breast cancer.

Identification of epithelial and mesenchymal circulating tumor cells in clonal lineage of an aggressive prostate cancer case

Little is known about the complexity and plasticity of circulating tumor cell (CTC) biology in different compartments of the fluid microenvironment during tumor metastasis. Here we integrated phenomics, genomics, and targeted proteomics to characterize CTC phenotypic and genotypic heterogeneity in paired peripheral blood (PB) and bone marrow aspirate (BMA) from a metastatic prostate cancer patient following the rapid disease progression, using the High-Definition Single Cell Assay 3.0 (HDSCA3.0). Uniquely, we identified a subgroup of genetically clonal CTCs that acquired a mesenchymal-like state and its presence was significantly associated with one subclone that emerged along the clonal lineage. Higher CTC abundance and phenotypic diversity were observed in the BMA than PB and differences in genomic alterations were also identified between the two compartments demonstrating spatial heterogeneity. Single cell copy number profiling further detected clonal heterogeneity within clusters of CTCs (also known as microemboli or aggregates) as well as phenotypic variations by targeted proteomics. Overall, these results identify epithelial and mesenchymal CTCs in the clonal lineage of an aggressive prostate cancer case and also demonstrate a single cell multi-omic approach to deconvolute the heterogeneity and association of CTC phenotype and genotype in multi-medium liquid biopsies of metastatic prostate cancer.

Chemokines in Triple-Negative Breast Cancer Heterogeneity: New Challenges for Clinical Implications

Tumor heterogeneity is a hallmark of cancer and one of the primary causes of resistance to therapies. Triple-negative breast cancer (TNBC), which accounts for 15% to 20% of all breast cancers and is the most aggressive subtype, is very diverse, connected to metastatic potential and response to therapy. It is a very diverse disease at the molecular, pathologic, and clinical levels. TNBC is substantially more likely to recur and has a worse overall survival rate following diagnosis than other breast cancer subtypes. Chemokines, low molecular weight proteins that stimulate chemotaxis, have been shown to control the cues responsible for TNBC heterogeneity. In this review, we have focused on tumor heterogeneity and the role of chemokines in modulating tumor heterogeneity, since this is the most critical issue in treating TNBC. Additionally, we examined numerous cues mediated by chemokine networks that contribute to the heterogeneity of TNBC. Recent developments in our knowledge of the chemokine networks that regulate TNBC heterogeneity may pave the door for developing difficult-to-treat TNBC treatment options.

Breast cancer circulating tumor cells with mesenchymal features-an unreachable target?

Circulating tumor cells (CTCs) mediate dissemination of solid tumors and can be an early sign of disease progression. Moreover, they show a great potential in terms of non-invasive, longitudinal monitoring of cancer patients. CTCs have been extensively studied in breast cancer (BC) and were shown to present a significant phenotypic plasticity connected with initiation of epithelial-mesenchymal transition (EMT). Apart from conferring malignant properties, EMT affects CTCs recovery rate, making a significant portion of CTCs from patients’ samples undetected. Wider application of methods and markers designed to isolate and identify mesenchymal CTCs is required to expand our knowledge about the clinical impact of mesenchymal CTCs. Therefore, here we provide a comprehensive review of clinical significance of mesenchymal CTCs in BC together with statistical analysis of previously published data, in which we assessed the suitability of a number of methods/markers used for isolation of CTCs with different EMT phenotypes, both in in vitro spike-in tests with BC cell lines, as well as clinical samples. Results of spiked-in cell lines indicate that, in general, methods not based on epithelial enrichment only, capture mesenchymal CTCs much more efficiently that CellSearch^® (golden standard in CTCs detection), but at the same time are not much inferior to Cell Search^®, though large variation in recovery rates of added cells among the methods is observed. In clinical samples, where additional CTCs detection markers are needed, positive epithelial-based CTCs enrichment was the most efficient in isolating CTCs with mesenchymal features from non-metastatic BC patients. From the marker side, PI3K and VIM were contributing the most to detection of CTCs with mesenchymal features (in comparison to SNAIL) in non-metastatic and metastatic BC patients, respectively. However, additional data are needed for more robust identification of markers for efficient detection of CTCs with mesenchymal features.

Mesenchymal Characteristics and Predictive Biomarkers on Circulating Tumor Cells for Therapeutic Strategy

Metastasis-related events are the primary cause of cancer-related deaths, and circulating tumor cells (CTCs) have a pivotal role in metastatic relapse. CTCs include a variety of subtypes with different functional characteristics. Interestingly, the epithelial-mesenchymal transition (EMT) markers expressed in CTCs are strongly associated with poor clinical outcome and related to the acquisition of circulating tumor stem cell (CTSC) features. Recent studies have revealed the existence of CTC clusters, also called circulating tumor microemboli (CTM), which have a high metastatic potential. In this review, we present current opinions regarding the clinical significance of CTCs and CTM with a mesenchymal phenotype as clinical surrogate markers, and we summarize the therapeutic strategy according to phenotype characterization of CTCs in various types of cancers for future precision medicine.

Inflammation-Based Scores Increase the Prognostic Value of Circulating Tumor Cells in Primary Breast Cancer

A correlation between circulating tumor cells (CTCs) and monocytes in metastatic breast cancer (BC), where CTCs and monocyte-to-lymphocyte ratio (MLR) were predictors of overall survival (OS), was recently shown. Herein, we aimed to assess the association between CTCs and the complete blood count (CBC)-derived inflammation-based scores in 284 primary BC patients. CTCs were determined in CD45-depleted peripheral blood mononuclear cells by real time-PCR. This method allowed us to detect a subset of CTCs with an epithelial-to-mesenchymal transition phenotype (CTC EMT), previously associated with inferior outcomes in primary BC. In the present study, CTC EMT positivity (hazard ratio (HR) = 2.4; 95% CI 1.20–4.66, p = 0.013) and elevated neutrophil-to-lymphocyte ratio (NLR) (HR = 2.20; 95% CI 1.07–4.55; p = 0.033) were associated with shorter progression-free survival (PFS) in primary BC patients. Multivariate analysis showed that CTC EMT-positive patients with NLR ≥ 3 had 8.6 times increased risk of disease recurrence (95% CI 2.35–31.48, p = 0.001) compared with CTC EMT-negative patients with NLR < 3. Similarly, disease recurrence was 13.14 times more likely in CTC EMT-positive patients with MLR ≥ 0.34 (95% CI 4.35–39.67, p < 0.001). Given its low methodological and financial demands, the CBC-derived inflammation-based score determination could, after broader validation, significantly improve the prognostication of BC patients.

Epithelial-Mesenchymal Plasticity in Circulating Tumor Cells, the Precursors of Metastasis

Circulating tumor cells offer an unprecedented window into the metastatic cascade, and to some extent can be considered as intermediates in the process of metastasis. They exhibit dynamic oscillations in epithelial to mesenchymal plasticity and provide important opportunities for prognosis, therapy response monitoring, and targeting of metastatic disease. In this manuscript, we review the involvement of epithelial-mesenchymal plasticity in the early steps of metastasis and what we have learned about its contribution to genomic instability and genetic diversity, tumor progression and therapeutic responses using cell culture, mouse models and circulating tumor cells enriched from patients.

Phase II study of Radium-223 dichloride combined with hormonal therapy for hormone receptor-positive, bone-dominant metastatic breast cancer

Background

Radium‐223 dichloride (Ra‐223) is a targeted alpha therapy that induces localized cytotoxicity in bone metastases. We evaluated the efficacy and safety of Ra‐223 plus hormonal therapy in hormone receptor‐positive (HR+), bone‐dominant metastatic breast cancer.

Methods

In this single‐center phase II study, 36 patients received Ra‐223 (55 kBq/kg intravenously every 4 weeks) up to 6 cycles with endocrine therapy. The primary objective was to determine the clinical disease control rate at 9 months. Secondary objectives were to determine (a) tumor response rate at 6 months, (b) progression‐free survival (PFS) durations, and (c) safety.

Results

The median number of prior systemic treatments for metastatic disease was 1 (range, 0‐4). The disease control rate at 9 months was 49%. The tumor response rate at 6 months was 54% (complete response, 21%; partial, 32%). The median PFS was 7.4 months (95% CI, 4.8‐not reached [NR]). The median bone‐PFS was 16 months (95% CI, 7.3‐NR). There were no grade 3/4 adverse events.

Conclusions

Ra‐223 with hormonal therapy showed possible efficacy in HR+ bone‐dominant breast cancer metastasis, and adverse events were tolerable. We plan to further investigate the clinical application of Ra‐223 in these patients. (NCT02366130).

Targets, pitfalls and reference materials for liquid biopsy tests in cancer diagnostics

Assessment of cell free DNA (cfDNA) and RNA (cfRNA), circulating tumor cells (CTC) and extracellular vesicles (EV) in blood or other bodily fluids can enable early cancer detection, tumor dynamics assessment, minimal residual disease detection and therapy monitoring. However, few liquid biopsy tests progress towards clinical application because results are often discordant and challenging to reproduce. Reproducibility can be enhanced by the development and implementation of standard operating procedures and reference materials to identify and correct for pre-analytical variables. In this review we elaborate on the technological considerations, pre-analytical variables and the use and availability of reference materials for the assessment of liquid biopsy targets in blood and highlight initiatives towards the standardization of liquid biopsy testing.

Incorporating MicroRNA into Molecular Phenotypes of Circulating Tumor Cells Enhances the Prognostic Accuracy for Patients with Metastatic Breast Cancer

The molecular phenotype of circulating tumor cells is associated with clinical outcome of patients with breast cancer. The aim of this study was to enhance the prognostic accuracy of the circulating tumor cell phenotype in metastatic breast cancer by incorporating miRNA into a combined prediction model.

Background.

The molecular phenotype of circulating tumor cells (CTCs) was associated with clinical outcome of patients with breast cancer. CTCs isolated from patients with metastatic breast cancer (MBC) display a unique microRNA (miRNA) expression profile. The aim of this study was to enhance the prognostic accuracy of the CTC phenotype in patients with MBC, by incorporating miRNA into a combined prediction model.

Subjects, Materials, and Methods.

CTCs were detected by CellSearch and enriched by magnetic cell sorting. miRNA deep sequencing and quantitative polymerase chain reaction were used to screen and verify potentially CTC‐specific miRNA candidates. Patients with MBC were enrolled from two independent cohorts, and overall survival (OS) and chemotherapy response were analyzed.

Results.

We screened and identified that miR‐106b was an upregulated molecule in patients with MBC with CTC ≥5/7.5 mL (n = 16) compared with patients with CTC = 0/7.5 mL (n = 16) and healthy donors (n = 8). The expression of CTC‐specific miR‐106b correlated with vimentin and E‐cadherin in CTC and acted as an independent factor for predicting OS (hazard ratio 2.157, 95% confidence interval [CI] 1.098–4.239, p = .026). Although CTC‐specific miR‐106b, E‐cadherin, and vimentin showed a prognostic potential independently, the prognostic performance for OS based on the combination of three markers was significantly enhanced in Cohort 1 (area under the curve [AUC] 0.752, 95% CI 0.658–0.847, n = 128) and further validated in Cohort 2 (AUC 0.726, 95% CI 0.595–0.856, n = 91). Besides, a combined model incorporating miR‐106b was associated with therapy response.

Conclusion.

The phenotypic assemblies of CTC incorporating miR‐106b show enhanced prognostic accuracy of overall survival in patients with MBC.

Implications for Practice.

In order to enhance the prognostic accuracy of the circulating tumor cell (CTC) phenotype in patients with metastatic breast cancer (MBC), this study screened and identified a CTC‐specific microRNA (miRNA), miR‐106b, as an upregulated molecule based on the comparison of miRNA profile between CTCs, primary tumors, and healthy blood donors. By incorporating miR‐106b into a combined prediction model, the prognostic accuracy of the CTC phenotype for patients with MBC was greatly improved in both the training and validation cohorts. This work provides clinical evidence supporting the prognostic potential of CTC‐specific miRNA for patients with MBC. These results indicate that developing CTC‐specific miRNAs as new biomarkers will help to further optimize personalized therapy.

Prognostic Significance of TWIST1, CD24, CD44, and ALDH1 Transcript Quantification in EpCAM-Positive Circulating Tumor Cells from Early Stage Breast Cancer Patients

(1) Background: The aim of the study was to evaluate the prognostic significance of EMT-associated (TWIST1) and stem-cell (SC) transcript (CD24, CD44, ALDH1) quantification in EpCAM+ circulating tumor cells (CTCs) of early breast cancer patients. (2) Methods: 100 early stage breast cancer patients and 19 healthy donors were enrolled in the study. CD24, CD44, and ALDH1 transcripts of EpCAM⁺ cells were quantified using a novel highly sensitive and specific quadraplex RT-qPCR, while TWIST1 transcripts were quantified by single RT-qPCR. All patients were followed up for more than 5 years. (3) Results: A significant positive correlation between overexpression of TWIST1 and CD24^−/low/CD44^high profile was found. Kaplan–Meier analysis revealed that the ER/PR-negative (HR-) patients and those patients with more than 3 positive lymph nodes that overexpressed TWIST1 in EpCAM⁺ cells had a significant lower DFI (log rank test; p < 0.001, p < 0.001) and OS (log rank test; p = 0.006, p < 0.001). Univariate and multivariate analysis also revealed the prognostic value of TWIST1 overexpression and CD24^−/low/CD44^high and CD24^−/low/ALDH1^high profile for both DFI and OS. (4) Conclusions: Detection of TWIST1 overexpression and stem-cell (CD24, CD44, ALDH1) transcripts in EpCAM⁺ CTCs provides prognostic information in early stage breast cancer patients.

Insights on CTC Biology and Clinical Impact Emerging from Advances in Capture Technology

Circulating tumor cells (CTCs) and circulating tumor microemboli (CTM) have been shown to correlate negatively with patient survival. Actual CTC counts before and after treatment can be used to aid in the prognosis of patient outcomes. The presence of circulating tumor materials (CTMat) can advertise the presence of metastasis before clinical presentation, enabling the early detection of relapse. Importantly, emerging evidence is indicating that cancer treatments can actually increase the incidence of CTCs and metastasis in pre-clinical models. Subsequently, the study of CTCs, their biology and function are of vital importance. Emerging technologies for the capture of CTC/CTMs and CTMat are elucidating vitally important biological and functional information that can lead to important alterations in how therapies are administered. This paves the way for the development of a "liquid biopsy" where treatment decisions can be informed by information gleaned from tumor cells and tumor cell debris in the blood.

Tumor associated macrophages induce epithelial to mesenchymal transition via the EGFR/ERK1/2 pathway in head and neck squamous cell carcinoma

The development of head and neck squamous cell carcinoma (HNSCC) is closely associated with inflammation. Tumor associated macrophages (TAMs), the largest population of inflammatory cells in the tumor stroma, serve an important role in accelerating cancer progression. The present study aimed to investigate the role of TAMs in the metastasis of HNSCC. TAM biomarkers and epithelial to mesenchymal transition (EMT)-associated proteins were detected using immunohistochemical and immunofluorescence staining in HNSCC. Then, direct and indirect co-culture systems of TAMs and HNSCC cells were established. The EMT-associated proteins and associated signaling pathways in HNSCC cells of the co-culture system were measured by reverse transcription-quantitative polymerase chain reaction and western blotting. Finally, hierarchical clustering was performed to analyze associations among TAM biomarkers, epidermal growth factor receptor (EGFR), activated extracellular signal-regulated protein kinase 1/2 (ERK1/2) and EMT-associated proteins in HNSCC tissues. The results indicated that the expression of EMT-associated proteins was positively associated with M2 macrophage biomarkers in HNSCC tissues. Cal27 cells were isolated from the co-culture system by fluorescence-activated cell sorting, and it was identified that E-cadherin was downregulated in Cal27 cells, while Vimentin and Slug were upregulated. Furthermore, the results indicated that EGF released by M2 macrophages in the co-culture served an important role by activating ERK1/2. The correlation and cluster analyses indicated that activated ERK1/2 was positively correlated with cluster of differentiation-163, EGFR, Vimentin and Slug. This suggested that TAMs may induce the EMT of cancer cells by activating the EGFR/ERK1/2 signaling pathway in HNSCC, which may be a promising approach to suppressing cancer metastasis.

Establishment of a multimarker qPCR panel for the molecular characterization of circulating tumor cells in blood samples of metastatic breast cancer patients during the course of palliative treatment

Background

Circulating tumor cells (CTC) are discussed to be an ideal surrogate marker for individualized treatment in metastatic breast cancer (MBC) since metastatic tissue is often difficult to obtain for repeated analysis. We established a nine gene qPCR panel to characterize the heterogeneous CTC population in MBC patients including epithelial CTC, their receptors (EPCAM, ERBB2, ERBB3, EGFR) CTC in Epithelial-Mesenchymal-Transition [(EMT); PIK3CA, AKT2), stem cell-like CTC (ALDH1) as well as resistant CTC (ERCC1, AURKA] to identify individual therapeutic targets.

Results

At TP0, at least one marker was detected in 84%, at TP1 in 74% and at TP2 in 79% of the patients, respectively. The expression of ERBB2, ERBB3 and ERCC1 alone or in combination with AURKA was significantly associated with therapy failure. ERBB2 + CTC were only detected in patients not receiving ERBB2 targeted therapies which correlated with no response. Furthermore, patients responding at TP2 had a significantly prolonged overall-survival than patients never responding (p = 0.0090).

Patients and Methods

2 × 5 ml blood of 62 MBC patients was collected at the time of disease progression (TP0) and at two clinical staging time points (TP1 and TP2) after 8–12 weeks of chemo-, hormone or antibody therapy for the detection of CTC (AdnaTest EMT-2/StemCell Select™, QIAGEN Hannover GmbH, Germany). After pre-amplification, multiplex qPCR was performed. Establishment was performed using various cancer cell lines. PTPRC (Protein tyrosine phosphatase receptor type C) and GAPDH served as controls.

Conclusions

Monitoring MBC patients using a multimarker qPCR panel for the characterization of CTC might help to treat patients accordingly in the future.

Molecular regulation of epithelial-to-mesenchymal transition in tumorigenesis (Review)

Numerous studies over the past two decades have focused on the epithelial-to-mesenchymal transition (EMT) and its role in the development of metastasis. Certain studies highlighted the importance of EMT in the dissemination of tumor cells and metastasis of epithelium-derived carcinomas. Tumor metastasis is a multistep process during which tumor cells change their morphology, and start to migrate and invade distant sites. The present review discusses the current understanding of the molecular mechanisms contributing to EMT in embryogenesis, fibrosis and tumorigenesis. Additionally, the signaling pathways that initiate EMT through transcriptional factors responsible for the activation and suppression of various genes associated with cancer cell migration were investigated. Furthermore, the important role of the epigenetic modifications that regulate EMT and the reverse process, mesenchymal-to-epithelial transition (MET) are discussed. MicroRNAs are key regulators of various intracellular processes and current knowledge of EMT has significantly improved due to microRNA characterization. Their effect on signaling pathways and the ensuing events that occur during EMT at the molecular level is becoming increasingly recognized. The current review also highlights the role of circulating tumor cells (CTCs) and CTC clusters, and their ability to form metastases. In addition, the biological properties of different types of circulating cells based on their tumor-forming potential are compared.

Tumor Heterogeneity in Breast Cancer

Breast cancer is a heterogeneous disease and differs greatly among different patients (intertumor heterogeneity) and even within each individual tumor (intratumor heterogeneity). Clinical and morphologic intertumor heterogeneity is reflected by staging systems and histopathologic classification of breast cancer. Heterogeneity in the expression of established prognostic and predictive biomarkers, hormone receptors, and human epidermal growth factor receptor 2 oncoprotein is the basis for targeted treatment. Molecular classifications are indicators of genetic tumor heterogeneity, which is probed with multigene assays and can lead to improved stratification into low- and high-risk groups for personalized therapy. Intratumor heterogeneity occurs at the morphologic, genomic, transcriptomic, and proteomic levels, creating diagnostic and therapeutic challenges. Understanding the molecular and cellular mechanisms of tumor heterogeneity that are relevant to the development of treatment resistance is a major area of research. Despite the improved knowledge of the complex genetic and phenotypic features underpinning tumor heterogeneity, there has been only limited advancement in diagnostic, prognostic, or predictive strategies for breast cancer. The current guidelines for reporting of biomarkers aim to maximize patient eligibility for targeted therapy, but do not take into account intratumor heterogeneity. The molecular classification of breast cancer is not implemented in routine clinical practice. Additional studies and in-depth analysis are required to understand the clinical significance of rapidly accumulating data. This review highlights inter- and intratumor heterogeneity of breast carcinoma with special emphasis on pathologic findings, and provides insights into the clinical significance of molecular and cellular mechanisms of heterogeneity.

A Novel Workflow to Enrich and Isolate Patient-Matched EpCAMhigh and EpCAMlow/negative CTCs Enables the Comparative Characterization of the PIK3CA Status in Metastatic Breast Cancer

Circulating tumor cells (CTCs), potential precursors of most epithelial solid tumors, are mainly enriched by epithelial cell adhesion molecule (EpCAM)-dependent technologies. Hence, these approaches may overlook mesenchymal CTCs, considered highly malignant. Our aim was to establish a workflow to enrich and isolate patient-matched EpCAM^high and EpCAM^low/negative CTCs within the same blood samples, and to investigate the phosphatidylinositol 3-kinase catalytic subunit alpha (PIK3CA) mutational status within single CTCs. We sequentially processed metastatic breast cancer (MBC) blood samples via CellSearch^® (EpCAM-based) and via Parsortix™ (size-based) systems. After enrichment, cells captured in Parsortix™ cassettes were stained in situ for nuclei, cytokeratins, EpCAM and CD45. Afterwards, sorted cells were isolated via CellCelector™ micromanipulator and their genomes were amplified. Lastly, PIK3CA mutational status was analyzed by combining an amplicon-based approach with Sanger sequencing. In 54% of patients′ blood samples both EpCAM^high and EpCAM^low/negative cells were identified and successfully isolated. High genomic integrity was observed in 8% of amplified genomes of EpCAM^low/negative cells vs. 28% of EpCAM^high cells suggesting an increased apoptosis in the first CTC-subpopulation. Furthermore, PIK3CA hotspot mutations were detected in both EpCAM^high and EpCAM^low/negative CTCs. Our workflow is suitable for single CTC analysis, permitting—for the first time—assessment of the heterogeneity of PIK3CA mutational status within patient-matched EpCAM^high and EpCAM^low/negative CTCs.

Epithelial-to-mesenchymal transition, circulating tumor cells and cancer metastasis: Mechanisms and clinical applications

Epithelial-to-mesenchymal transition (EMT) endows epithelial cells with enhanced motility and invasiveness, allowing them to participate in many physiological and pathological processes. Epithelial-to-mesenchymal transition contributes to the generation of circulating tumor cells (CTCs) in epithelial cancers because it increases tumor cell invasiveness, promotes tumor cell intravasation and ensures tumor cell survival in the peripheral system. Although the contribution of epithelial-to-mesenchymal transition to tumor cell invasiveness has been confirmed, the role epithelial-to-mesenchymal transition plays in metastasis remains debated. As a favorable material for a “liquid biopsy”, circulating tumor cells have been shown to have promising values in the clinical management of tumors. Furthermore, an increasing number of studies have begun to explore the value of CTC-related biomarkers, and some studies have found that the expression of EMT and stemness markers in circulating tumor cells, in addition to CTC detection, can provide more information on tumor diagnosis, treatment, prognosis and research.

Circulating tumor cell status monitors the treatment responses in breast cancer patients: a meta-analysis

Whether circulating tumor cells (CTCs) can be used as an indicator of treatment response in breast cancer (BC) needs to be clarified. We addressed this issue by a meta-analysis. PubMed, EMBase and Cochrane library databases were searched in June 2016. Effect measures were estimated as pooled risk ratio (RR), odds ratio (OR) or mean difference by fixed- or random-effect models, according to heterogeneity of included studies. In total, 50 studies with 6712 patients were recruited. Overall analysis showed that there was a significant reduction of CTC-positive rate (RR = 0.68, 95% CI: 0.61–0.76, P < 0.00001) after treatment. Subgroup analyses revealed that neoadjuvant treatment, adjuvant treatment, metastatic treatment or combination therapy could reduce the CTC-positive rate, but surgery could not; moreover, the reduction was only found in HER2+ or HER2- patients but not in the triple-negative ones. Reduction of CTC-positive rate was associated with lower probability of disease progression (OR = 0.54, 95% CI: 0.33–0.89, P = 0.01) and longer overall survival period (mean difference = 11.61 months, 95% CI: 8.63–14.59, P < 0.00001) as well as longer progression-free survival period (mean difference = 5.07 months, 95% CI: 2.70–7.44, P < 0.0001). These results demonstrate that CTC status can serve as an indicator to monitor the effectiveness of treatments and guide subsequent therapies in BC.

Enrichment, Isolation and Molecular Characterization of EpCAM-Negative Circulating Tumor Cells

The presence of EpCAM-positive circulating tumor cells (CTCs) in the peripheral blood is associated with poor clinical outcomes in breast, colorectal and prostate cancer, as well as the prognosis of other tumor types. In addition, recent studies have suggested that the presence of CTCs undergoing epithelial-to-mesenchymal transition and, as such, may exhibit reduced or no expression of epithelial proteins e.g. EpCAM, might be related to disease progression in metastatic breast cancer (MBC) patients. Analyzing the neoplastic nature of this EpCAM-low/negative (EpCAM-neg) subpopulation remains an open issue as the current standard detection methods for CTCs are not efficient at identifying this subpopulation of cells. The possible association of EpCAM-neg CTCs with EpCAM-positive (EpCAM-pos) CTCs and role in the clinicopathological features and prognosis of MBC patients has still to be demonstrated. Several technologies have been developed and are currently being tested for the identification and the downstream analyses of EpCAM-pos CTCs. These technologies can be adapted and implemented into workflows to isolate and investigate EpCAM-neg cells to understand their biology and clinical relevance. This chapter will endeavour to explain the rationale behind the identification and analyses of all CTC subgroups, as well as to review the current strategies employed to enrich, isolate and characterize EpCAM-negative CTCs. Finally, the latest findings in the field will briefly be discussed with regard to their clinical relevance.

Epithelial-mesenchymal transition in tumor metastasis

The epithelial-mesenchymal transition (EMT) is a developmental program that enables stationary epithelial cells to gain the ability to migrate and invade as single cells. Tumor cells reactivate EMT to acquire molecular alterations that enable the partial loss of epithelial features and partial gain of a mesenchymal phenotype. Our understanding of the contribution of EMT to tumor invasion, migration, and metastatic outgrowth has evolved over the past decade. In this review, we provide a summary of both historic and recent studies on the role of EMT in the metastatic cascade from various experimental systems, including cancer cell lines, genetic mouse tumor models, and clinical human breast cancer tissues.

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.

Circulating and disseminated tumour cells - mechanisms of immune surveillance and escape

Metastatic spread of tumour cells is the main cause of cancer-related deaths. Understanding the mechanisms of tumour-cell dissemination has, therefore, become an important focus for cancer research. In patients with cancer, disseminated cancer cells are often detectable in the peripheral blood as circulating tumour cells (CTCs) and in the bone marrow or lymph nodes as disseminated tumour cells (DTCs). The identification and characterization of CTCs and DTCs has yielded important insights into the mechanisms of metastasis, resulting in a better understanding of the molecular alterations and profiles underlying drug resistance. Given the expanding role of immunotherapies in the treatment of cancer, interactions between tumour cells and immune cells are the subject of intense research. Theoretically, cancer cells that exit the primary tumour site - leaving the protection of the typically immunosuppressive tumour microenvironment - will be more vulnerable to attack by immune effector cells; thus, the survival of tumour cells after dissemination might be the 'Achilles' heel' of metastatic progression. In this Review, we discuss findings relating to the interactions of CTCs and DTCs with the immune system, in the context of cancer immuno-editing, evasion from immune surveillance, and formation of metastases.

Does the mobilization of circulating tumour cells during cancer therapy cause metastasis?

Despite progressive improvements in the management of patients with locoregionally confined, advanced-stage solid tumours, distant metastasis remains a very common - and usually fatal - mode of failure after attempted curative treatment. Surgery and radiotherapy are the primary curative modalities for these patients, often combined with each other and/or with chemotherapy. Distant metastasis occurring after treatment can arise from previously undetected micrometastases or, alternatively, from persistent locoregional disease. Another possibility is that treatment itself might sometimes cause or promote metastasis. Surgical interventions in patients with cancer, including biopsies, are commonly associated with increased concentrations of circulating tumour cells (CTCs). High CTC numbers are associated with an unfavourable prognosis in many cancers. Radiotherapy and systemic antitumour therapies might also mobilize CTCs. We review the preclinical and clinical data concerning cancer treatments, CTC mobilization and other factors that might promote metastasis. Contemporary treatment regimens represent the best available curative options for patients who might otherwise die from locally confined, advanced-stage cancers; however, if such treatments can promote metastasis, this process must be understood and addressed therapeutically to improve patient survival.

MINDEC-An Enhanced Negative Depletion Strategy for Circulating Tumour Cell Enrichment

Most current methods of circulating tumour cell (CTC) enrichment target the epithelial protein EpCAM, which is commonly expressed in adenocarcinoma cells. However, such methods will not recover the fraction of CTCs that have a non-epithelial phenotype due to epithelial–mesenchymal transition. For phenotype-independent CTC enrichment, we developed a new enhanced negative depletion strategy—termed MINDEC—that is based on multi-marker (CD45, CD16, CD19, CD163, and CD235a/GYPA) depletion of blood cells rather than targeted enrichment of CTCs. Here we validated the performance of MINDEC using epithelial and mesenchymal cancer cell lines, demonstrating a mean recovery of 82 ± 10%, high depletion (437 ± 350 residual white blood cells (WBCs)/mL peripheral blood), linearity between spiked and recovered cells (correlation coefficient: r = 0.995), and a low detection limit (≥1 cell recovered in all four replicates spiked with 3 cells). For clinical validation of this method, we enumerated CTCs in peripheral blood samples from patients with metastatic pancreatic cancer, detecting CTCs in 15 of 21 blood samples (71%) from 9 patients. The promising performance of the MINDEC enrichment strategy in our study encourages validation in larger clinical trials.

Analysis of tumor template from multiple compartments in a blood sample provides complementary access to peripheral tumor biomarkers

Targeted cancer therapeutics are promised to have a major impact on cancer treatment and survival. Successful application of these novel treatments requires a molecular definition of a patient's disease typically achieved through the use of tissue biopsies. Alternatively, allowing longitudinal monitoring, biomarkers derived from blood, isolated either from circulating tumor cell derived DNA (ctcDNA) or circulating cell-free tumor DNA (ccfDNA) may be evaluated. In order to use blood derived templates for mutational profiling in clinical decisions, it is essential to understand the different template qualities and how they compare to biopsy derived template DNA as both blood-based templates are rare and distinct from the gold-standard. Using a next generation re-sequencing strategy, concordance of the mutational spectrum was evaluated in 32 patient-matched ctcDNA and ccfDNA templates with comparison to tissue biopsy derived DNA template. Different CTC antibody capture systems for DNA isolation from patient blood samples were also compared. Significant overlap was observed between ctcDNA, ccfDNA and tissue derived templates. Interestingly, if the results of ctcDNA and ccfDNA template sequencing were combined, productive samples showed similar detection frequency (56% vs 58%), were temporally flexible, and were complementary both to each other and the gold standard. These observations justify the use of a multiple template approach to the liquid biopsy, where germline, ctcDNA, and ccfDNA templates are employed for clinical diagnostic purposes and open a path to comprehensive blood derived biomarker access.

Stem cell technology in breast cancer: current status and potential applications

Breast cancer, the leading cause of cancer among females, is supported by the presence of a rare subset of undifferentiated cells within the tumor, identified as breast cancer stem cells (BCSCs). BCSCs underlie the mechanisms of tumor initiation and sustenance and are implicated in the dissemination of the primary tumor to metastatic sites, as they have been found circulating in the blood of breast cancer patients. The discovery of BCSCs has generated a great amount of interest among the scientific community toward their isolation, molecular characterization, and therapeutic targeting. In this review, after summarizing the literature on molecular characterization of BCSCs and methodologies used for their isolation, we will focus on recent data supporting their molecular and functional heterogeneity. Additionally, following a synopsis of the latest approaches for BCSC targeting, we will specifically emphasize on the therapeutic use of naïve or engineered normal stem cells in the treatment of breast cancer and present contradictory findings challenging their safety.

Expression of SOCS1 and CXCL12 Proteins in Primary Breast Cancer Are Associated with Presence of Circulating Tumor Cells in Peripheral Blood

Circulating tumor cells (CTCs) are independent prognostic factors in the primary and metastatic breast cancer patients and play crucial role in hematogenous tumor dissemination. The aim of this study was to correlate the presence of CTCs in peripheral blood with the expression of proteins in tumor tissue that have a putative role in regulation of cell growth and metastatic potential. This prospective study included 203 primary breast cancer patients treated by definitive surgery. CTCs were detected by quantitative real-time PCR for the expression of epithelial (CK19) or epithelial-to-mesenchymal transition–inducing transcription factor genes (TWIST1, SNAIL1, SLUG, and ZEB1). Expression of APC, ADAM23, CXCL12, E-cadherin, RASSF1, SYK, TIMP3, BRMS1, and SOCS1 proteins in primary breast tumor tissue was evaluated by immunohistochemistry. CTCs with epithelial markers were found in 17 (9.2%) patients. Their occurrence was associated with inhibition of SOCS1 expression (odds ratio [OR] = 0.07; 95% confidence interval [CI], 0.03-0.13; P < .001). CTCs with positive epithelial-to-mesenchymal transition markers were detected in 30 (15.8%) patients; however, no association with analyzed protein expressions was found. Overall, CTCs were detected in 44 (22.9%) patients. Presence of any CTC marker was significantly associated with positive CXCL12 expression (OR = 3.08; 95% CI, 1.15-8.26; P = .025) and lack of SOCS1 expression (OR = 0.10; 95% CI, 0.04-0.25; P < .001) in patient’s tumor tissues. As both CXCL12 and SOCS1 proteins are involved in cytokine signaling, our results provide support for the hypothesis that aberrant signaling cross talk between cytokine and chemokine responses could have an important role in hematogenous dissemination of tumor cells in breast cancer.

Gene expression profiling of single circulating tumor cells in ovarian cancer - Establishment of a multi-marker gene panel

The presence of circulating tumor cells (CTCs) in the blood of ovarian cancer patients was shown to correlate with decreased overall survival, whereby CTCs with epithelial-mesenchymal-transition (EMT) or stem-like traits are supposed to be involved in metastatic progression and recurrence. Thus, investigating the transcriptional profiles of CTCs might help to identify therapy resistant tumor cells and to overcome treatment failure. For this purpose, we established a multi-marker panel for the molecular characterization of single CTCs, detecting epithelial (EpCAM, Muc-1, CK5/7), EMT (N-cadherin, Vimentin, Snai1/2, CD117, CD146, CD49f) and stem cell (CD44, ALDH1A1, Nanog, SOX2, Notch1/4, Oct4, Lin28) associated transcripts. First primer specificity and PCR-performance of the multiplex-RT-PCRs were successfully validated on genomic DNA and cDNA isolated from OvCar3 cells. The assay sensitivity of the epithelial panel was evaluated by adding defined numbers of tumor cells into the blood of healthy donors and performing a subsequent immunomagnetic tumor cell enrichment (AdnaTest OvarianCancerSelect), resulting in a 100% concordance for the epithelial markers EpCAM and Muc-1 to the AdnaTest OvarianCancerDetect. Additionally, by processing blood from ovarian cancer patients, high assay sensitivity could be verified. In blood of healthy donors no signals for epithelial markers were detected, for EMT and stem cell markers, however, signals were obtained mainly originating from leukocytes which calls for single cell analysis. To that aim by using the ovarian cancer cell line OvCar3, we successfully established a workflow enabling the characterization of single CTCs. It consists of a density gradient-dependent enrichment for nucleated cells, a depletion of CD45-positive cells of hematopoietic origin followed by immunofluorescent labeling of CTCs by EpCAM and Muc-1. Single CTCs are then isolated by micromanipulation and processed for panel gene expression profiling. Finally, fifteen single CTCs from three ovarian cancer patients were analyzed and found to be positive for stem cell (CD44, ALDH1A1, Nanog, Oct4) and EMT markers (N-cadherin, Vimentin, Snai2, CD117, CD146). Albeit, inter-cellular and intra/inter-patient heterogeneity and co-expression of epithelial, mesenchymal and stem cell transcripts on the same CTC was observed. We have established a robust workflow to perform sensitive single cell panel gene expression analysis without the need of pre-amplification steps. Our data point towards a heterogeneous expression of stem cell and EMT associated transcripts in ovarian cancer CTCs.

CXCR4-SDF-1 interaction potentially mediates trafficking of circulating tumor cells in primary breast cancer

Background

Cytokines are involved in cancer invasion and metastasis. Circulating tumor cells (CTCs) play key role in tumor dissemination and are an independent survival predictor in breast cancer patients. The aim of this study was to assess correlation between CTCs and plasma cytokines in primary breast cancer (PBC) patients.

Methods

This study included 147 chemotherapy naïve PBC patients. Peripheral blood mononuclear cells (PBMC) were depleted of hematopoetic cells using RossetteSep™ negative selection kit. RNA extracted from CD45-depleted PBMC was interrogated for expression of EMT (Twist1, Snail1, Slug, Zeb1) and epithelial (Ck19) gene transcripts by qRT-PCR. The concentrations of 51 plasma cytokines were measured using multiplex bead arrays.

Results

CTCs were detected in 25.2 % patients. CTCs exhibiting only epithelial markers (CTC_EP) and only EMT markers (CTC_EMT) were present evenly in 11.6 % patients, while CTCs co-expressing both markers were detected in 2.0 % patients. Patients with presence of CTC_EP in peripheral blood had significantly elevated levels of plasma IFN-α2, IL-3, MCP-3, β-NGF, SCF, SCGF-β, TNF-β and SDF-1 compared to patients without CTC_EP. CTC_EP exhibited overexpression of SDF-1 receptor and CXCR4, but not other corresponding cytokine receptor, and in multivariate analysis SDF-1 was independently associated with CTC_EP. There was an inverse correlation between CTC_EMT and plasma cytokines CTACK, β-NGF and TRAIL, while presence of either subtype of CTCs was associated with increased level of TGF-β2.

Conclusion

Using cytokine profiling, we identified cytokines associated with CTCs subpopulations in peripheral blood of PBC. Our data suggest that CXCR4-SDF-1 axis is involved in mobilization and trafficking of epithelial CTCs.

Capture and Identification of Heterogeneous Circulating Tumor Cells Using Transparent Nanomaterials and Quantum Dots-Based Multiplexed Imaging

Background: Capture and identification of circulating tumor cells (CTCs) in the blood system can help guide therapy and predict the prognosis of cancer patients. However, simultaneous capture and identification of CTCs with both epithelial and mesenchymal phenotypes remains a formidable technical challenge for cancer research. This study aimed at developing a system to efficiently capture and identify these CTCs with heterogeneous phenotypes using transparent nanomaterials and quantum dots (QDs)-based multiplexed imaging.

Methods: Hydroxyapatite-chitosan (HA-CTS) nanofilm-coated substrates were modified based on our previous work to increase the capture efficiency of cancer cell lines by extending baking and incubating time. QDs-based imaging was applied to detect cytokeratin, epithelial cell adhesion molecule (EpCAM), and vimentin of cancer cells to demonstrate the feasibility of multiplexed imaging. And QDs-based multiplexed imaging of CD45, cytokeratin and vimentin was applied to detect CTCs from different cancer patients that were captured using HA-CTS nanofilm substrates.

Results: Comparisons of the capture efficiencies of cancer cells at different baking time of film formation and incubating time of cell capture revealed the optimal baking and incubating time. Optimal time was chosen to develop a modified CTCs capture system that could capture EpCAM-positive cancer cells at an efficiency > 80%, and EpCAM-negative cancer cells at an efficiency > 50%. QDs-based imaging exhibited comparable detection ability but higher photostability compared to organic dyes imaging in staining cells. In addition, QDs-based multiplexed imaging also showed the molecular profiles of cancer cell lines with different phenotypes well. The integrated CTCs capture and identification system successfully captured and imaged CTCs with different sub-phenotypes in blood samples from cancer patients.

Conclusion: This study demonstrated a reliable capture and detection system for heterogeneous CTCs that combined enrichment equipment based on HA-CTS nanofilm substrates with QDs-based multiplexed imaging.

Circulating tumor cells as early predictors of metastatic spread in breast cancer patients with limited metastatic dissemination

Introduction

Traditional factors currently used for prognostic stratification do not always adequately predict treatment response and disease evolution in advanced breast cancer patients. Therefore, the use of blood-based markers, such as circulating tumor cells (CTCs), represents a promising complementary strategy for disease monitoring. In this retrospective study, we explored the role of CTC counts as predictors of disease evolution in breast cancer patients with limited metastatic dissemination.

Methods

A total of 492 advanced breast cancer patients who had a CTC count assessed by CellSearch prior to starting a new line of systemic therapy were eligible for this analysis. Using the threshold of 5 CTCs/7.5 ml of blood, pretreatment CTC counts were correlated in the overall population with metastatic site distribution, evaluated at baseline and at the time of treatment failure, using Fisher’s exact test. Time to visceral progression and time to the development of new metastatic lesions and sites were estimated in patients with nonvisceral metastases and with single-site metastatic disease, respectively, by the Kaplan-Meier method. Survival times were compared between groups according to pretreatment CTC count by logrank test.

Results

In the overall population, a pretreatment level ≥5 CTCs/7.5 ml was associated with an increased baseline number of metastatic sites compared with <5 CTCs/7.5 ml (P = 0.0077). At the time of treatment failure, patients with ≥5 CTCs/7.5 ml more frequently developed new metastatic lesions and sites compared with those with <5 CTCs/7.5 ml (development of new lesions: P = 0.0002; development of new sites: P = 0.0031). Among patients with disease originally confined to nonvisceral sites, ≥5 CTCs/7.5 ml was associated with remarkably shorter time to visceral metastases (P = 0.0021) and overall survival (P = 0.0006) compared with <5 CTCs/7.5 ml. In patients with single-site metastatic disease, ≥5 CTCs/7.5 ml was associated with a significant reduction of the time to development of new metastatic sites (P = 0.0051) and new lesions (P = 0.0002) and with worse overall survival (P = 0.0101).

Conclusion

Our results suggest that baseline CTC counts can be used as an early predictor of metastatic potential in breast cancer patients with limited metastatic dissemination.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-014-0440-8) contains supplementary material, which is available to authorized users.

Expression of stem cell and epithelial-mesenchymal transition markers in circulating tumor cells of breast cancer patients

Evaluation and characterization of circulating tumor cells (CTCs) have become a major focus of translational cancer research. Presence of CTCs predicts worse clinical outcome in early and metastatic breast cancer. Whether all cells from the primary tumor have potential to disseminate and form subsequent metastasis remains unclear. As part of the metastatic cascade, tumor cells lose their cell-to-cell adhesion and undergo epithelial-mesenchymal transition (EMT) in order to enter blood circulation. During EMT epithelial antigens are downregulated; thus, such tumor cells might elude classical epithelial marker-based detection. Several researchers postulated that some CTCs express stem cell-like phenotype; this might lead to chemoresistance and enhanced metastatic potential of such cells. In the present review, we discuss current data on EMT and stem cell markers in CTCs of breast cancer and their clinical significance.

Circulating tumour cells: the evolving concept and the inadequacy of their enrichment by EpCAM-based methodology for basic and clinical cancer research

Increasing evidence suggests that circulating tumour cells (CTCs) are responsible for metastatic relapse and this has fuelled interest in their detection and quantification. Although numerous methods have been developed for the enrichment and detection of CTCs, none has yet reached the 'gold' standard. Since epithelial cell adhesion molecule (EpCAM)-based enrichment of CTCs offers several advantages, it is one of the most commonly used and has been adapted for high-throughput technology. However, emerging evidence suggests that CTCs are highly heterogeneous: they consist of epithelial tumour cells, epithelial-to-mesenchymal transition (EMT) cells, hybrid (epithelial/EMT(+)) tumour cells, irreversible EMT(+) tumour cells, and circulating tumour stem cells (CTSCs). The EpCAM-based approach does not detect CTCs expressing low levels of EpCAM and non-epithelial phenotypes such as CTSCs and those that have undergone EMT and no longer express EpCAM. Thus, the approach may lead to underestimation of the significance of CTCs, in general, and CTSCs and EMT(+) tumour cells, in particular, in cancer dissemination. Here, we provide a critical review of research literature on the evolving concept of CTCs and the inadequacy of their enrichment by EpCAM-based technology for basic and clinical cancer research. The review also outlines future perspectives in the field.

Interplay of Stem Cell Characteristics, EMT, and Microtentacles in Circulating Breast Tumor Cells

Metastasis, not the primary tumor, is responsible for the majority of breast cancer-related deaths. Emerging evidence indicates that breast cancer stem cells (CSCs) and the epithelial-to-mesenchymal transition (EMT) cooperate to produce circulating tumor cells (CTCs) that are highly competent for metastasis. CTCs with both CSC and EMT characteristics have recently been identified in the bloodstream of patients with metastatic disease. Breast CSCs have elevated tumorigenicity required for metastatic outgrowth, while EMT may promote CSC character and endows breast cancer cells with enhanced invasive and migratory potential. Both CSCs and EMT are associated with a more flexible cytoskeleton and with anoikis-resistance, which help breast carcinoma cells survive in circulation. Suspended breast carcinoma cells produce tubulin-based extensions of the plasma membrane, termed microtentacles (McTNs), which aid in reattachment. CSC and EMT-associated upregulation of intermediate filament vimentin and increased detyrosination of α-tubulin promote the formation of McTNs. The combined advantages of CSCs and EMT and their associated cytoskeletal alterations increase metastatic efficiency, but understanding the biology of these CTCs also presents new therapeutic targets to reduce metastasis.

Colorectal cancer diagnostics: biomarkers, cell-free DNA, circulating tumor cells and defining heterogeneous populations by single-cell analysis

Reliable biomarkers are needed to guide treatment of colorectal cancer, as well as for surveillance to detect recurrence and monitor therapeutic response. In this review, the authors discuss the use of various biomarkers in addition to serum carcinoembryonic antigen, the current surveillance method for metastatic recurrence after resection. The clinical relevance of mutations including microsatellite instability, KRAS, BRAF and SMAD4 is addressed. The role of circulating tumor cells and cell-free DNA with regards to their implementation into clinical use is discussed, as well as how single-cell analysis may fit into a monitoring program. The detection and characterization of circulating tumor cells and cell-free DNA in colorectal cancer patients will not only improve the understanding of the development of metastasis, but may also supplant the use of other biomarkers.

New frontiers in circulating tumor cell analysis: A reference guide for biomolecular profiling toward translational clinical use

Circulating tumor cells (CTCs) are now routinely isolated from blood, and measurement of CTC concentrations appears to correlate well with survival in patients with cancer. Interrogation of the molecular profile of CTCs for expression of protein biomarkers, genetic variants and gene expression provides opportunities to use this information to guide personalized treatment, monitor therapy and detect emerging resistance. However, successful application of profiling techniques requires analyses that deliver a reliable and clinically relevant representation of a patient's cancer as it changes with time. Here, we comprehensively review the current knowledge of therapeutically relevant biomarkers in isolated CTCs obtained by fluorescence imaging and genomic profiling approaches. The reviewed data support the notion that molecular profiling of CTCs will provide a reliable representation or surrogate index of tumor burden. Large-scale translational trials, many currently in progress, will provide critical data to progress CTC analysis toward wider clinical use in personalized treatment.

Essentials of circulating tumor cells for clinical research and practice

The major cause of death due to cancer is its metastatic deposit in numerous tissues and organs. The metastatic process requires the migration of malignant cells from primary sites to distant environments. Even for tumors initially spreading through lymphatic vessels, hematogenous transport is the most common metastatic pathway. The detachment of cancer cells from a primary tumor into the blood stream is called epithelial-mesenchymal transition (EMT). As these cells circulate further in the bloodstream they are known as circulating tumor cells (CTCs). The CTC population is highly resilient, enabling the cells to colonize a foreign microenvironment. Alternatively, cancer stem cells (CSCs) may arise from differentiated cancer cells through EMT and an embryonic transdifferentiation process. The presence of CTCs/CSCs in blood seems to be a determining factor of metastasis. This paper reviews various methods of clinical cancer detection as well as the biology and molecular characterization of CTCs/CSCs. Our goal was to summarize clinical studies which used CTC/CSCs for prognosis in patients with breast, colorectal, prostate, lung, ovarian, and bladder cancer.

Tissue-based identification of stem cells and epithelial-to-mesenchymal transition in breast cancer

Pathologists have recognized breast cancer heterogeneity for decades, but its causes were unknown. In recent years, basic science and translational studies have demonstrated that cancer stem cells contribute to the heterogeneous histologic and functional characteristics of breast cancer. Even more recently, the ability of breast epithelial cells to undergo an epithelial-to-mesenchymal transition has been linked to the acquisition of stem cells properties and enhanced tumor invasion, metastasis, and resistance to available treatments. The stem cells and cells undergoing epithelial-to-mesenchymal transition are attractive targets for therapy and breast cancer prevention. Despite current challenges, their identification in breast tissue samples would enable pathologists to discover and validate prognostic and predictive markers as well as identify markers of increased risk for breast cancer.