Prognostic Relevance of Viable Circulating Tumor Cells Detected by EPISPOT in Metastatic Breast Cancer Patients

Circulating Tumor Cells: Moving Biological Insights into Detection

Circulating tumor cells (CTCs) have shown promising potential as liquid biopsies that facilitate early detection, prognosis, therapeutic target selection and monitoring treatment response. CTCs in most cancer patients are low in abundance and heterogeneous in morphological and phenotypic profiles, which complicate their enrichment and subsequent characterization. Several methodologies for CTC enrichment and characterization have been developed over the past few years. However, integrating recent advances in CTC biology into these methodologies and the selection of appropriate enrichment and characterization methods for specific applications are needed to improve the reliability of CTC biopsies. In this review, we summarize recent advances in the studies of CTC biology, including the mechanisms of their generation and their potential forms of existence in blood, as well as the current CTC enrichment technologies. We then critically examine the selection of methods for appropriately enriching CTCs for further investigation of their clinical applications.

Isolation of Phenotypically Distinct Cancer Cells Using Nanoparticle-Mediated Sorting

Isolating subpopulations of heterogeneous cancer cells is an important capability for the meaningful characterization of circulating tumor cells at different stages of tumor progression and during the epithelial-to-mesenchymal transition. Here, we present a microfluidic device that can separate phenotypically distinct subpopulations of cancer cells. Magnetic nanoparticles coated with antibodies against the epithelial cell adhesion molecule (EpCAM) are used to separate breast cancer cells in the microfluidic platform. Cells are sorted into different zones on the basis of the levels of EpCAM expression, which enables the detection of cells that are losing epithelial character and becoming more mesenchymal. The phenotypic properties of the isolated cells with low and high EpCAM are then assessed using matrix-coated surfaces for collagen uptake analysis, and an NAD(P)H assay that assesses metabolic activity. We show that low-EpCAM expressing cells have higher collagen uptake and higher folate-induced NAD(P)H responses compared to those of high-EpCAM expressing cells. In addition, we tested SKBR3 cancer cells undergoing chemically induced hypoxia. The induced cells have reduced expression of EpCAM, and we find that these cells have higher collagen uptake and NAD(P)H metabolism relative to noninduced cells. This work demonstrates that nanoparticle-mediated binning facilitates the isolation of functionally distinct cell subpopulations and allows surface marker expression to be associated with invasiveness, including collagen uptake and metabolic activity.

How to study and overcome tumor heterogeneity with circulating biomarkers: The breast cancer case

Breast cancer ranks first among female cancer-related deaths in Western countries. As the primary tumor can often be controlled by surgical resection, the survival of women with breast cancer is closely linked to the incidence of distant metastases. Molecular screening by next generation sequencing highlighted the spatial and temporal heterogeneity of solid tumors as well as the clonal evolution of cancer cells during progression and under treatment pressure. Such findings question whether an optimal assessment of disease progression and a screening for druggable mutations should be based on molecular features of primary or recurrent/metastatic lesions and therefore represent a crucial element for failure or success of personalized medicine. In fact, new targeted therapies may induce only short-term benefit annulled by the emergence of resistant clones with new driver mutations which would need to be rapidly and reliably identified. Serial tissue sampling is therefore essential but, unfortunately, also represents a problem since biopsies from solid lesions, which are invasive and potentially painful and risky, cannot be easily repeatedly sampled, are inaccessible or may not fully reflect tumor heterogeneity. The need to early detect and strike this "moving target" is now directing the scientific community toward liquid biopsy-based biomarkers, which include circulating tumor cells (CTC) and cell-free circulating tumor DNA (ctDNA), can be repeatedly assessed through non-invasive and easy-to-perform procedures and may act as reliable read-outs of functional and molecular features of recurrent/metastatic lesions. In this review we summarize the outcome of CTCs and ctDNA in breast cancer, with special reference on their role on unveiling and overcoming tumor heterogeneity, on their potential relevance for tumor surveillance and monitoring, and for the selection of therapeutic options. Finally, we propose integration between blood-based molecular and clinical approaches for monitoring disease progression according to the specific pattern of recurrence of the most aggressive breast cancer molecular subtypes.

Clinical Applications of Circulating Tumor Cells in Pharmacotherapy: Challenges and Perspectives

Screening for circulating tumor cells (CTCs) has been identified as one approach to ultrasensitive liquid biopsy in real-time monitoring of cancer patients. The detection of CTCs in peripheral blood from cancer patients is promising as a diagnostic tool; however, the application of CTCs in therapeutic treatment still faces serious challenges with respect to specificity and sensitivity. Here, we review the significant roles of CTCs in metastasis and the strengths and weaknesses of the currently available methods for CTC detection and characterization. Moreover, we discuss the clinical application of CTCs as markers for patient prognosis, and we specifically focus on the application of CTCs as indicators in cancer pharmacotherapy. Characterization of the detected CTCs will provide new biologic perspectives and clinical applications for the treatment of cancer patients with metastasis.

Prognostic value of circulating tumor cells in the peripheral blood of patients with esophageal squamous cell carcinoma

OBJECTIVE

Circulating tumor cells (CTCs) of patients with malignant tumors can be used as a prognostic marker. However, there are few relevant reports to date on esophageal squamous cell carcinoma (ESCC). Our study assesses the clinical significance of CTCs in ESCC patients.

PATIENTS AND METHODS

CTCs were detected in 103 peripheral blood (PB) samples from 59 ESCC patients. Correlation between CTCs and clinical parameters was analyzed using the χ² test or Fisher's exact test. Overall survival (OS) and progression-free survival (PFS) were analyzed using Kaplan-Meier analysis and univariate and multivariate methods.

RESULTS

The CTC detection rate was 79.7% (47/59) at baseline. The frequency of CTC-positive patients increased as the disease stage advanced (88.0% in stages III-IV, 58.9% in stages I-II). CTC counts ≥0/7.5 mL of PB were correlated with the degree of tumor differentiation, tumor infiltration, and lymph node and distant metastases. Overall, the OS and PFS of patients with CTC counts ≥3 or ≥5/7.5 mL of PB before surgery were significantly shorter than those of patients with CTC counts <3 or <5/7.5 mL. Multivariate analysis showed CTC counts ≥5/7.5 mL of PB to be a strong prognostic indicator of OS (hazard ratio [HR] 12.478; 95% confidence interval [CI], 8.2-34.3; P<0.05) and PFS (HR 6.524; 95% CI, 1.2-34.3; P<0.05) in ESCC patients. Patients in whom CTCs changed from positive at baseline to a negative value after surgery had an excellent prognosis.

CONCLUSION

CTCs might serve as a reference indicator for the prognosis and monitoring of disease progression and treatment effects in ESCC.

Detecting Blood-Based Biomarkers in Metastatic Breast Cancer: A Systematic Review of Their Current Status and Clinical Utility

Reviews on circulating biomarkers in breast cancer usually focus on one single biomarker or a selective group of biomarkers. An overview summarizing the discovery and evaluation of all blood-based biomarkers in metastatic breast cancer is lacking. This systematic review aims to identify the available evidence of known blood-based biomarkers in metastatic breast cancer, regarding their clinical utility and state-of-the-art position in the validation process. The initial search yielded 1078 original studies, of which 420 were assessed for eligibility. A total of 320 studies were included in the final synthesis. A Development, Evaluation and Application Chart (DEAC) of all biomarkers was developed. Most studies focus on identifying new biomarkers and search for relations between these biomarkers and traditional molecular characteristics. Biomarkers are usually investigated in only one study (68.8%). Only 9.8% of all biomarkers was investigated in more than five studies. Circulating tumor cells, gene expression within tumor cells and the concentration of secreted proteins are the most frequently investigated biomarkers in liquid biopsies. However, there is a lack of studies focusing on identifying the clinical utility of these biomarkers, by which the additional value still seems to be limited according to the investigated evidence.

Monitoring multiple myeloma by next-generation sequencing of V(D)J rearrangements from circulating myeloma cells and cell-free myeloma DNA

Recent studies suggest that circulating tumor cells and cell-free DNA may represent powerful non-invasive tools for monitoring disease in patients with solid and hematologic malignancies. Here, we conducted a pilot study in 27 myeloma patients to explore the clonotypic V(D)J rearrangement for monitoring circulating myeloma cells and cell-free myeloma DNA. Next-generation sequencing was used to define the myeloma V(D)J rearrangement and for subsequent peripheral blood tracking after treatment initiation. Positivity for circulating myeloma cells/cell-free myeloma was associated with conventional remission status (P<0.001) and 91% of non-responders/progressors versus 41% of responders had evidence of persistent circulating myeloma cells/cell-free myeloma DNA (P<0.001). About half of the partial responders showed complete clearance of circulating myeloma cells/cell-free myeloma DNA despite persistent M-protein, suggesting that these markers are less inert than the M-protein, rely more on cell turnover and, therefore, decline more rapidly after initiation of effective treatment. Positivity for circulating myeloma cells and for cell-free myeloma DNA were associated with each other (P=0.042), but discordant in 30% of cases. This indicates that cell-free myeloma DNA may not be generated entirely by circulating myeloma cells and may reflect overall tumor burden. Prospective studies need to define the predictive potential of high-sensitivity determination of circulating myeloma cells and DNA in the monitoring of multiple myeloma.

Circulating Tumor Cells: Fluid Surrogates of Solid Tumors

Evaluation of circulating tumor cells (CTCs) has demonstrated clinical validity as a prognostic tool based on enumeration, but since the introduction of this tool to the clinic in 2004, further clinical utility and widespread adoption have been limited. However, immense efforts have been undertaken to further the understanding of the mechanisms behind the biology and kinetics of these rare cells, and progress continues toward better applicability in the clinic. This review describes recent advances within the field, with a particular focus on understanding the biological significance of CTCs, and summarizes emerging methods for identifying, isolating, and interrogating the cells that may provide technical advantages allowing for the discovery of more specific clinical applications. Included is an atlas of high-definition images of CTCs from various cancer types, including uncommon CTCs captured only by broadly inclusive nonenrichment techniques.

Isolation of label-free and viable circulating tumour cells (CTCs) from blood samples of cancer patients through a two-step process: negative selection-type immunomagnetic beads and spheroid cell culture-based cell isolation

A two-step CTCs purification method to isolate viable, label-free, all possible, and purity improved CTCs.

EpCAM-Independent Enrichment and Detection of Viable Circulating Tumor Cells Using the EPISPOT Assay

Identification and characterization of circulating tumor cells (CTCs) in peripheral blood can provide information on the direction and the efficacy of treatments. Current techniques such as CellSearch^® are limited in differentiating between apoptotic and viable CTCs. In contrast, the fluorescent EPISPOT assay allows for the identification of viable cells by detecting proteins secreted/released/shed by functional single epithelial cancer cells. In addition, as CTCs are rare events, it is required to combine the EPISPOT assay with an enrichment step. In this article, the EPISPOT assay, as well as two technologies for enrichment of viable CTCs, RosetteSep™ and Parsortix™ techniques, will be presented and discussed in detail.

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.

Technical challenges in the isolation and analysis of circulating tumor cells

Increasing evidence suggests that cancer cells display dynamic molecular changes in response to systemic therapy. Circulating tumor cells (CTCs) in the peripheral blood represent a readily available source of cancer cells with which to measure this dynamic process. To date, a large number of strategies to isolate and characterize CTCs have been described. These techniques, however, each have unique limitations in their ability to sensitively and specifically detect these rare cells. In this review we focus on the technical limitations and pitfalls of the most common CTC isolation and detection strategies. Additionally, we emphasize the difficulties in correctly classifying rare cells as CTCs using common biomarkers. As for assays developed in the future, the first step must be a uniform and clear definition of the criteria for assigning an object as a CTC based on disease-specific biomarkers.

Circulating Tumor Cells and Circulating Tumor DNA: Challenges and Opportunities on the Path to Clinical Utility

Recent technological advances have enabled the detection and detailed characterization of circulating tumor cells (CTC) and circulating tumor DNA (ctDNA) in blood samples from patients with cancer. Often referred to as a "liquid biopsy," CTCs and ctDNA are expected to provide real-time monitoring of tumor evolution and therapeutic efficacy, with the potential for improved cancer diagnosis and treatment. In this review, we focus on these opportunities as well as the challenges that should be addressed so that these tools may eventually be implemented into routine clinical care.

The prognostic role of circulating tumor cells in lung cancer

INTRODUCTION

Circulating tumor cells (CTCs) can be isolated from the peripheral blood of cancer patients. Several studies to assess the prognostic and/or predictive role of CTCs have been performed in lung cancer patients.

AREAS COVERED

The state-of-the-art of the role of CTCs in lung cancer patients is reviewed and discussed. A structured search of bibliographic databases for peer-reviewed research literature and of main meetings using a focused review question was undertaken. Expert commentary: Although in the revised studies different technologies, cutoffs, patients' populations and statistical approaches have been used, a high CTCs count as prognostic role in small-cell lung cancer is suggested, whereas additional studies are required to confirm this correlation in non-small-cell lung cancer. A reduction in CTCs count is also likely to be correlated with the lung cancer patients' outcome. Large prospective trials need to confirm the prognostic and/or predictive role of CTCs in lung cancer.

[Advances in Liquid Biopsy and its Clinical Application in the Diagnosis and Treatment of Non-small Cell Lung Cancer]

随着近几年科学技术的进步，液体活检技术也有了长足的发展，并在肿瘤的早期诊断及后期治疗中扮演着越来越重要的角色。相比于传统的组织活检，液体活检以其独有的无创性、便捷性、高重复性等特点在临床上得到更多的青睐，在未来有着巨大的发展潜力。本文重点探讨了循环肿瘤细胞（circulating tumor cells, CTCs）和循环肿瘤DNA（circulating tumor DNA, ctDNA），作为液体活检最重要的两个检测对象，其历史、生物学特性，检测手段，局限性及其在非小细胞肺癌诊治中的应用。

The Role of CTCs as Tumor Biomarkers

Detection of Circulating Tumor Cells (CTCs) in peripheral blood can serve as a "liquid biopsy" approach and as a source of valuable tumor markers. CTCs are rare, and thus their detection, enumeration and molecular characterization are very challenging. CTCs have the unique characteristic to be non-invasively isolated from blood and used to follow patients over time, since these cells can provide significant information for better understanding tumour biology and tumour cell dissemination. CTCs molecular characterization offers the unique potential to understand better the biology of metastasis and resistance to established therapies and their analysis presents nowadays a promising field for both advanced and early stage patients. In this chapter we focus on the latest findings concerning the clinical relevance of CTC detection and enumeration, and discuss their potential as tumor biomarkers in various types of solid cancers. We also highlight the importance of performing comparison studies between these different methodologies and external quality control systems for establishing CTCs as tumor biomarkers in the routine clinical setting.

Circulating tumor cell technologies†

Circulating tumor cells, a component of the “liquid biopsy”, hold great potential to transform the current landscape of cancer therapy. A key challenge to unlocking the clinical utility of CTCs lies in the ability to detect and isolate these rare cells using methods amenable to downstream characterization and other applications. In this review, we will provide an overview of current technologies used to detect and capture CTCs with brief insights into the workings of individual technologies. We focus on the strategies employed by different platforms and discuss the advantages of each. As our understanding of CTC biology matures, CTC technologies will need to evolve, and we discuss some of the present challenges facing the field in light of recent data encompassing epithelial‐to‐mesenchymal transition, tumor‐initiating cells, and CTC clusters.

We present a comprehensive overview of CTC detection and capture technologies.

We provide a conceptual description of strategies used in different technologies.

We highlight the key features of individual technologies.

We discuss CTC technology performance in the context of clinical studies.

Functional studies on circulating and disseminated tumor cells in carcinoma patients

Despite numerous clinical studies indicating the clinical relevance of circulating tumor cells (CTCs) in blood and disseminated tumor cells (DTCs) in the bone marrow of cancer patients, the functional properties of these cells are largely unknown. The focus of this review is to emphasize how functional studies on viable CTCs and DTCs can enlarge the spectrum of applications of "liquid biopsies". The low number of CTCs in the peripheral blood and DTCs in the bone marrow and the fact that carcinoma cells are difficult to culture are major challenges. Significant advances in the in vitro and in vivo expansion of CTCs and DTCs from cancer patients have been achieved, which enable us now to study the functional properties of these cells. Here, we discuss published data about functional studies on CTCs and DTCs using in vitro cultivation and in vivo xenograft models. Functional analyses on CTCs and DTCs offer the possibility to identify the metastasis-initiating cells. Moreover, CTC-derived cell lines and xenografts might point to new therapeutic targets and can be used for drug development.

Circulating tumor cells in breast cancer

Over the past decade, technically reliable circulating tumor cell (CTC) detection methods allowed the collection of large datasets of CTC counts in cancer patients. These data can be used either as a dynamic prognostic biomarker or as tumor material for “liquid biopsy”. Breast cancer appears to be the cancer type in which CTC have been the most extensively studied so far, with level‐of‐evidence‐1 studies supporting the clinical validity of CTC count in both early and metastatic stage. This review summarizes and discusses the clinical results obtained in breast cancer patients, the issues faced by the molecular characterization of CTC and the biological findings about cancer biology and metastasis that were obtained from CTC.

In metastatic breast cancer, CTC count is a level‐of‐evidence 1 prognostic dynamic biomarker.

Several interventional trials are ongoing to demonstrate the clinical utility of CTC detection in metastatic breast cancer.

In early breast cancer, CTC count is also a prognostic biomarker, not correlated with the other usual prognostic factors.

Molecular characterization of CTC is promising, trials with anti‐HER2 therapy are ongoing.

Functional Studies on Viable Circulating Tumor Cells

BACKGROUND

Research on circulating tumor cells (CTCs) as new biomarkers has received great attention over the past decade. In particular, the capture and analysis of CTCs as "liquid biopsies" provides the possibility to avoid invasive tissue biopsies, with obvious implications in cancer diagnostics.

CONTENT

The focus of this review is to describe and discuss how functional studies on viable CTCs can enlarge the spectrum of applications of liquid biopsies, with emphasis on breast, prostate, colon, and lung cancer as the major tumor entities in industrialized countries. The low number of CTCs in the peripheral blood of most cancer patients makes challenging the in vitro culture of CTCs. Epithelial tumor cells are difficult to culture, even when starting with millions of tumor cells. Recently, several groups have achieved important advances in the in vitro and in vivo expansion of CTCs from cancer patients at very advanced stages with higher amounts of CTCs. Here, we present current technologies to enrich and detect viable human CTCs, including positive and negative enrichment strategies that are based on antigen expression and physical properties of CTCs. We also discuss published data about functional studies on CTCs that use in vitro and in vivo models.

SUMMARY

Functional analyses on CTCs offer the possibility to identify the biological properties of metastatic cells, including the identification of metastasis-initiating cells. Moreover, CTC-derived cell lines and xenografts might reveal new therapeutic targets and can be used for drug screening.

The potential diagnostic power of circulating tumor cell analysis for non-small-cell lung cancer

In non-small-cell lung cancer (NSCLC), genotyping tumor biopsies for targetable somatic alterations has become routine practice. However, serial biopsies have limitations: they may be technically difficult or impossible and could incur serious risks to patients. Circulating tumor cells (CTCs) offer an alternative source for tumor analysis that is easily accessible and presents the potential to identify predictive biomarkers to tailor therapies on a personalized basis. Examined here is our current knowledge of CTC detection and characterization in NSCLC and their potential role in EGFR-mutant, ALK-rearranged and ROS1-rearranged patients. This is followed by discussion of the ongoing issues such as the question of CTC partnership as diagnostic tools in NSCLC.

Circulating tumor cells in breast cancer--current status and perspectives

The phenomenon of tumor cell dissemination through the blood stream has been known since the 19th century. Circulating tumor cells (CTCs) may be detected in peripheral blood of patients with breast cancer and may serve as a surrogate marker for minimal residual disease. Prognostic relevance of CTCs has already been demonstrated in early and metastatic breast cancer and commercially available detection systems are currently employed in various clinical trials. Since peripheral blood is an easily accessible compartment, serial reevaluation of CTCs is possible and may contribute to better therapy monitoring. Another potential of CTCs lies in the characterization of tumor cells. Expression profiles may differ between CTCs and primary tumor, which may result in different responses to treatment. Assessment of molecular features of CTCs may be an important step for the optimization of adjuvant and metastatic systemic therapy.

Diagnostic Utility of Unbiased Circulating Tumour Cell Capture through Negative Depletion of Peripheral Blood Cells

OBJECTIVES

Cytological analysis of peripheral blood circulating tumour cells (CTCs) is a potential method of confirmatory clinical diagnosis of cancer. However, cell capture methods tend to be biased and captured cells are not usually portable resulting in difficulties in pathology reporting. We evaluated unbiased cell capture through depletion of unwanted normal cells and conventional clinical analyses of captured cells.

METHODS

Blood was sampled from 29 patients who underwent surgery for suspected lung cancer. It was processed using two different depletion cocktails. After depletion of unwanted cells, the resultant cell pellet was processed onto glass slides or embedded into FFPE blocks and stained using standard haematoxylin and eosin staining followed by cytopathologic assessment. Two pathologists performed the assessment independently.

RESULTS

The CTCs were identified in 38-45% of cases using CD45 depletion cocktail with the cell pellet processed on a glass slide, while other combinations of methods produced poorer results. Overall, there was a good concordance between the pathologists (up to 91.3%). The sensitivity of cancer diagnosis was 42% (95% CI 23-63%), while the specificity was 100% (95% CI 29-100%).

CONCLUSION

Negative depletion can be used to isolate CTCs in standard clinical settings; however, more effective ways of detection are required to increase the sensitivity of the diagnosis.

Liquid biopsy in cancer patients: advances in capturing viable CTCs for functional studies using the EPISPOT assay

Circulating tumor cells (CTCs) in the blood of cancer patients have received increasing attention as new diagnostic tool enabling 'liquid biopsies'. In contrast to the wealth of descriptive studies demonstrating the clinical relevance of CTCs as biomarkers, the extremely low concentration of CTCs in the peripheral blood of most cancer patients challenges further functional studies. This article discusses the current possibilities to enrich and, in particular, detect viable CTCs with emphasis on the EPithelial ImmunoSPOT technology. This functional assay detects viable CTCs at the single-cell level and has been used on hundreds of patients with different tumor types including epithelial tumors (breast, prostate and colon cancer) and melanomas. Moreover, the article summarizes recent advances in the in vitro and in vivo expansion of CTCs from cancer patients. These functional analyses will contribute to identifying the biological properties of metastatic cells and reveal new therapeutic targets against disseminating cancer cells.

Circulating tumor cells in breast cancer beyond the genotype of primary tumor for tailored therapy

Although TNM staging based on tumor, node lymph status and metastasis status-is the most widely used method in the clinic to classify breast cancer (BC) and assess prognosis, it offers limited information for different BC subgroups. Circulating tumor cells (CTCs) are regarded as minimal residual disease and are proven to have a strong relationship with BC. Detection of ≥5 CTCs per 7.5 mL in peripheral blood predicts poor prognosis in metastatic BC irrespective of other clinical parameters, whereas, in early-stage BC, detection of CK19(+) CTCs are also associated with poor prognosis. Increasing data and clinical trials show that CTCs can improve prognostic accuracy and help tailor treatment for patients with BC. However, heterogeneous CTCs in the process of an epithelial-mesenchymal transition (EMT) in BC makes it a challenge to detect these rare cells. Moreover, the genotypic and phenotypic features of CTCs are different from primary BC tumors. Molecular analysis of CTCs in BC may benefit patients by identifying those amenable to tailored therapy. We propose that CTCs should be used alongside the TNM staging system and the genotype of primary tumor to guide tailored BC diagnosis and treatment.

Sampling circulating tumor cells for clinical benefits: how frequent?

Circulating tumor cells (CTCs) are cells shed from tumors or metastatic sites and are a potential biomarker for cancer diagnosis, management, and prognostication. The majority of current studies use single or infrequent CTC sampling points. This strategy assumes that changes in CTC number, as well as phenotypic and molecular characteristics, are gradual with time. In reality, little is known today about the actual kinetics of CTC dissemination and phenotypic and molecular changes in the blood of cancer patients. Herein, we show, using clinical case studies and hypothetical simulation models, how sub-optimal CTC sampling may result in misleading observations with clinical consequences, by missing out on significant CTC spikes that occur in between sampling times. Initial studies using highly frequent CTC sampling are necessary to understand the dynamics of CTC dissemination and phenotypic and molecular changes in the blood of cancer patients. Such an improved understanding will enable an optimal, study-specific sampling frequency to be assigned to individual research studies and clinical trials and better inform practical clinical decisions on cancer management strategies for patient benefits.

Using circulating tumor cells to inform on prostate cancer biology and clinical utility

Substantial advances in the molecular biology of prostate cancer have led to the approval of multiple new systemic agents to treat men with metastatic castration-resistant prostate cancer (mCRPC). These treatments encompass androgen receptor directed therapies, immunotherapies, bone targeting radiopharmaceuticals and cytotoxic chemotherapies. There is, however, great heterogeneity in the degree of patient benefit with these agents, thus fueling the need to develop predictive biomarkers that are able to rationally guide therapy. Circulating tumor cells (CTCs) have the potential to provide an assessment of tumor-specific biomarkers through a non-invasive, repeatable "liquid biopsy" of a patient's cancer at a given point in time. CTCs have been extensively studied in men with mCRPC, where CTC enumeration using the Cellsearch® method has been validated and FDA approved to be used in conjunction with other clinical parameters as a prognostic biomarker in metastatic prostate cancer. In addition to enumeration, more sophisticated molecular profiling of CTCs is now feasible and may provide more clinical utility as it may reflect tumor evolution within an individual particularly under the pressure of systemic therapies. Here, we review technologies used to detect and characterize CTCs, and the potential biological and clinical utility of CTC molecular profiling in men with metastatic prostate cancer.

Circulating tumor cells: a multifunctional biomarker

One of the most promising developments in translational cancer medicine has been the emergence of circulating tumor cells (CTC) as a minimally invasive multifunctional biomarker. CTCs in peripheral blood originate from solid tumors and are involved in the process of hematogenous metastatic spread to distant sites for the establishment of secondary foci of disease. The emergence of modern CTC technologies has enabled serial assessments to be undertaken at multiple time points along a patient's cancer journey for pharmacodynamic (PD), prognostic, predictive, and intermediate endpoint biomarker studies. Despite the promise of CTCs as multifunctional biomarkers, there are still numerous challenges that hinder their incorporation into standard clinical practice. This review discusses the key technical aspects of CTC technologies, including the importance of assay validation and clinical qualification, and compares existing and novel CTC enrichment platforms. This article discusses the utility of CTCs as a multifunctional biomarker and focuses on the potential of CTCs as PD endpoints either directly via the molecular characterization of specific markers or indirectly through CTC enumeration. We propose strategies for incorporating CTCs as PD biomarkers in translational clinical trials, such as the Pharmacological Audit Trail. We also discuss issues relating to intrapatient heterogeneity and the challenges associated with isolating CTCs undergoing epithelial-mesenchymal transition, as well as apoptotic and small CTCs. Finally, we envision the future promise of CTCs for the selection and monitoring of antitumor precision therapies, including applications in single CTC phenotypic and genomic profiling and CTC-derived xenografts, and discuss the promises and limitations of such approaches. See ALL articles in this CCR focus section, "Progress in pharmacodynamic endpoints."

Establishment and characterization of a cell line from human circulating colon cancer cells

Circulating tumor cells (CTC) in blood are promising new biomarkers potentially useful for prognostic prediction and monitoring of therapies in patients with solid tumors including colon cancer. Moreover, CTC research opens a new avenue for understanding the biology of metastasis in patients with cancer. However, an in-depth investigation of CTCs is hampered by the very low number of these cells, especially in the blood of patients with colorectal cancer. Thus, the establishment of cell cultures and permanent cell lines from CTCs has become the most challenging task over the past year. Here, we describe, for the first time, the establishment of cell cultures and a permanent cell line from CTCs of one patient with colon cancer. The cell line designated CTC-MCC-41 has been cultured for more than one year, and the cells have been characterized at the genome, transcriptome, proteome, and secretome levels. This thorough analysis showed that CTC-MCC-41 cells resemble characteristics of the original tumor cells in the patient with colon cancer and display a stable phenotype characterized by an intermediate epithelial/mesenchymal phenotype, stem cell-like properties, and an osteomimetic signature, indicating a bone marrow origin. Functional studies showed that CTC-MCC-41 cells induced rapidly in vitro endothelial cell tube formation and in vivo tumors after xenografting in immunodeficient mice. The establishment of this first colon cancer CTC line allows now a wealth of functional studies on the biology of CTCs as well as in vitro and in vivo drug testing.

Circulating Tumor Cells: Who is the Killer?

This article is a critical note on the subject of Circulating Tumor Cells (CTC). It takes into account the tumor identity of Circulating Tumor Cells as cancer seeds in transit from primary to secondary soils, rather than as a “biomarker”, and considers the help this field could bring to cancer patients. It is not meant to duplicate information already available in a large number of reviews, but to stimulate considerations, further studies and development helping the clinical use of tumor cells isolated from blood as a modern personalized, non-invasive, predictive test to improve cancer patients’ life. The analysis of CTC challenges, methodological bias and critical issues points out to the need of referring to tumor cells extracted from blood without any bias and identified by cytopathological diagnosis as Circulating Cancer Cells (CCC). Finally, this article highlights recent developments and identifies burning questions which should be addressed to improve our understanding of the domain of CCC and their potential to change the clinical practice.

Challenges in circulating tumour cell research

During the past ten years, circulating tumour cells (CTCs) have received enormous attention as new biomarkers and the subject of basic research. Although CTCs are already used in numerous clinical trials, their clinical utility is still under investigation. Many issues regarding the detection and characterization of CTCs remain unknown. In this Opinion article, we propose a conceptual framework of CTC assays and point out current challenges of CTC research, which might structure this dynamic field of translational cancer research.

Blood-based analyses of cancer: circulating tumor cells and circulating tumor DNA

The ability to study nonhematologic cancers through noninvasive sampling of blood is one of the most exciting and rapidly advancing fields in cancer diagnostics. This has been driven both by major technologic advances, including the isolation of intact cancer cells and the analysis of cancer cell-derived DNA from blood samples, and by the increasing application of molecularly driven therapeutics, which rely on such accurate and timely measurements of critical biomarkers. Moreover, the dramatic efficacy of these potent cancer therapies drives the selection for additional genetic changes as tumors acquire drug resistance, necessitating repeated sampling of cancer cells to adjust therapy in response to tumor evolution. Together, these advanced noninvasive diagnostic capabilities and their applications in guiding precision cancer therapies are poised to change the ways in which we select and monitor cancer treatments.

SIGNIFICANCE

Recent advances in technologies to analyze circulating tumor cells and circulating tumor DNA are setting the stage for real-time, noninvasive monitoring of cancer and providing novel insights into cancer evolution, invasion, and metastasis.