Expected clinical applications of circulating tumor cells in breast cancer

Tumor cell invasion and intravascular filtration lead to the presence of circulating tumor cells (CTCs) in peripheral blood. CTCs have, thus, been counted in patients with cancer to analyze metastatic mechanisms or in the hope of developing clinical applications for diagnosis and therapy; various CTC-related studies have been performed. However, the clinical significance of CTCs remains to be established because of the extremely small number of CTCs in peripheral blood as compared with the number of blood cells. Technical problems (e.g. reproducibility and reliability) in the detection of CTCs also remain to be solved. The use of flow cytometric analysis, which can be performed with tumor-cell markers such as anti-epithelial cell adhesion molecule antibodies and anti-cytokeratin antibodies and non-tumor-cell markers such as anti-CD45 antibodies has enhanced specificity for the detection of tumor cells. The CellSearch System^® can detect 1 CTC in 7.5 mL of peripheral blood, with high reproducibility. Its detection rate and accuracy for CTCs have been confirmed. In the United States, clinical trials have used this system to detect CTCs in patients with metastatic breast cancer, metastatic colorectal cancer, and metastatic prostate cancer, and CTCs have been confirmed to be a useful prognostic factor. This system was also suggested to be useful for monitoring treatment response in patients with metastatic breast cancer and was approved by the United States Food and Drug Administration in 2004. Measuring CTC counts can facilitate the early prediction of treatment response and thereby avoid unnecessary therapy. CTCs may also be a useful biomarker for molecular targeted agents, enabling the identification of patients most likely to respond to a given treatment and facilitating treatment selection. However, the widespread use of CTC monitoring as a routine examination requires a further improvement in measurement sensitivity, the establishment of criteria for quantitative and qualitative evaluations, and additional clear-cut evidence supporting the clinical significance of CTCs. We expect that CTCs will be established to be a new diagnostic and therapeutic index for breast cancer.     

Clinical significance of circulating tumor cells in breast cancer patients

Circulating tumor cells (CTCs) are defined as tumor cells circulating in the peripheral blood of patients, shed from either the primary tumors or its metastases. Many techniques have been developed in the recent years to identify CTCs in breast cancer patients, and trials have proved the prognostic significance of CTCs. In this study, we validated the CTC detection method of combining cell filtration and laser scanning cytometry (LSC), which was highly reproducible with increased sensitivity and accuracy. In 134 non-metastatic breast cancer patients analyzed, HER2 was found to be the only primary tumor characteristics that correlated with the presence of CTCs. 85 patients with definitive stage information were selected for association study between the disease stages and CTC numbers. The detection rate and the number of CTCs were correlated with the disease stages. Moreover, assessment of CTCs in 92 metastatic breast cancer patients was found to be able to predict the efficacy of chemotherapy. Increase in CTC numbers was an independent prognostic factor for treatment outcomes. Our results suggested that CTC assessment could be an indication of the disease progression and analysis of the properties of CTCs is likely to provide new insights into the biology of breast cancer and contribute to defining novel treatments and better prediction of clinical outcomes.     

Circulating tumour cells, their role in metastasis and their clinical utility in lung cancer

Circulating tumour cells (CTCs) have attracted much recent interest in cancer research as a potential biomarker and as a means of studying the process of metastasis. It has long been understood that metastasis is a hallmark of malignancy, and conceptual theories on the basis of metastasis from the nineteenth century foretold the existence of a tumour "seed" which is capable of establishing discrete tumours in the "soil" of distant organs. This prescient "seed and soil" hypothesis accurately predicted the existence of CTCs; microscopic tumour fragments in the blood, at least some of which are capable of forming metastases. However, it is only in recent years that reliable, reproducible methods of CTC detection and analysis have been developed. To date, the majority of studies have employed the CellSearch? system (Veridex LLC), which is an immunomagnetic purification method. Other promising techniques include microfluidic filters, isolation of tumour cells by size using microporous polycarbonate filters and flow cytometry-based approaches. While many challenges still exist, the detection of CTCs in blood is becoming increasingly feasible, giving rise to some tantalizing questions about the use of CTCs as a potential biomarker. CTC enumeration has been used to guide prognosis in patients with metastatic disease, and to act as a surrogate marker for disease response during therapy. Other possible uses for CTC detection include prognostication in early stage patients, identifying patients requiring adjuvant therapy, or in surveillance, for the detection of relapsing disease. Another exciting possible use for CTC detection assays is the molecular and genetic characterization of CTCs to act as a "liquid biopsy" representative of the primary tumour. Indeed it has already been demonstrated that it is possible to detect HER2, KRAS and EGFR mutation status in breast, colon and lung cancer CTCs respectively. In the course of this review, we shall discuss the biology of CTCs and their role in metastagenesis, the most commonly used techniques for their detection and the evidence to date of their clinical utility, with particular reference to lung cancer.     

Circulating tumors cells as biomarkers: progress toward biomarker qualification

Personalized cancer medicine requires the development of tumor-specific biomarkers to optimize selection of targeted therapies and to better assess response to therapy. Current efforts in several tumor types have shown that patients in whom circulating tumor cells (CTCs) are detected have an inferior prognosis relative to those in whom CTCs are not detected and that the elimination or decrease of CTCs following treatment is associated with improved clinical outcomes. Technological advances in the detection, isolation, capture, and characterization of CTCs from phlebotomy samples obtained in a routine clinical practice setting have enabled the evaluation of different CTC biomarkers. Unmet needs in cancer diagnosis and treatment where CTC biomarkers have been studied include determining prognosis, assessing the effects of treatment, and as a source of tumor for the biologic identification and characterization of determinants to predict sensitivity to one form of treatment versus another and to understand mechanisms of treatment resistance.At present, there is no single definition of a CTC and no single CTC "biomarker." Rather, multiple assays (tests) are in development for CTC biomarkers. However, before the role of any biomarker in medical decision making can be determined, it is essential that the assays used to measure the biomarker are analytically validated in a sequence of trials to generate the evidence to support the biomarker's use in the given context of use. It is against this background that this review focuses on the process of developing CTC biomarker assays, with the objective of outlining the necessary steps to qualify specific CTC tests for medical decision making in clinical practice or drug development. The potential for point-of-care tests is clear.     

Circulating tumor cells as pharmacodynamic biomarker in early clinical oncological trials

Circulating tumor cells (CTCs) have received a lot of attention from both researchers and clinicians because of their prognostic value for progression-free and overall survival in selected tumor types. CTCs are readily available by single venipuncture, thereby posing little burden on the patient and allowing for repeated, sequential sampling during therapy. Nowadays, the sensitivity of several CTC detection and capture techniques allow for further characterization and analysis of specific targets of interest on the CTC itself. These techniques have given CTCs the potential to be used as a pharmacodynamic read-out in drug development. In this review, we explore the utility of CTCs as a pharmacodynamic biomarker in early clinical oncological trials. We present an overview of current literature on assays for CTCs as pharmacodynamic biomarker, their different targets of interest and their level of validation, followed by discussion of their limitations.     

Circulating Tumor Cells: Evolving Evidence and Future Challenges

Circulating tumor cells (CTCs) are rare malignant cells found in the peripheral blood that originate from the primary tumor or metastatic sites. New techniques have been developed to isolate and characterize these cells. CTC enumeration has been incorporated into different fields of oncology as a prognostic marker, a tool to monitor therapy response, and a method to understand basic tumor characteristics. This review covers the different techniques available for isolation of CTCs, the clinical utility of CTCs in breast, prostate, and colon cancer, and future directions in this field.     

Clinical application of circulating tumor cells in breast cancer

Circulating tumor cells (CTCs) play a major role in the metastatic spread of breast cancer. CTC detection has proven to be an important parameter for predicting progression free and overall survival. Collection of CTCs is minimally invasive and can be performed more often than disseminated tumor cell (DTC) collection from bone marrow, thus providing a real-time “liquid biopsy”. In this review, the most important techniques for enrichment and detection of CTCs are discussed for clinical application in low and higher staged breast cancer, as well as the genetic and molecular characterization of CTCs. For CTCs, the use of immunology-based enrichment techniques with multiple antibodies is recommended in a clinical setting, as well as the use of cytometric detection techniques, combined with RT-PCR for confirmation. Special attention is given to the value of cancer stem cell (CSC) activity, which may be the main cause of ineffectiveness of the control over metastatic lesions due to intratumor heterogeneity. Accumulating information on CSCs offers new paradigms to generate effective targets for the treatment of metastatic disease. Genetic and molecular characterization of CTCs has potential to stratify patients for optimal personalized treatment regimens. CTCs can be used for monitoring patients during treatment schedules.     

Towards a personalized breast cancer treatment approach guided by circulating tumor cell (CTC) characteristics

Circulating tumor cells (CTCs) can be found in the peripheral blood of patients with different solid tumors, including breast cancer. A CTC count is a strong established prognostic factor in various stages in several tumor types. Besides that, characterization of CTCs is expected to become an invaluable tool to predict treatment response and personalize cancer treatments. Likely, CTCs are shed by different tumor lesions and may therefore provide a comprehensive view of tumor characteristics at a certain time-point, including inter- and intratumoral heterogeneity. Obtained through a simple venipuncture, CTCs could this way serve as a “liquid biopsy”. However, isolation and subsequent characterization of CTCs is technically extremely challenging, mainly due to the small number of cells amidst a large majority of leukocytes. A wide range of assays has been developed, but only the CellSearch System® (Veridex, Raritan, NJ, USA) has obtained FDA approval for CTC enumeration so far. For characterization purposes, no assay has been validated at all. Nevertheless, the first studies investigating the clinical value of CTC characteristics have been performed. Here, we review these clinical studies. The various techniques used to interrogate CTCs are briefly described and an overview of the clinical relevance of CTC characterization in breast cancer is given.     

Molecular characterization of circulating tumor cells in breast cancer: challenges and promises for individualized cancer treatment

Blood testing using Circulating Tumor Cells (CTCs) has emerged as one of the hottest fields in cancer diagnosis. Research on CTCs present nowadays a challenge, as these cells are well defined targets for understanding tumour biology and improving cancer treatment. The presence of tumor cells in patient’s bone marrow or peripheral blood is an early indicator of metastasis and may signal tumor spread sooner than clinical symptoms appear and imaging results confirm a poor prognosis. CTC enumeration can serve as a “liquid biopsy” and an early marker to assess response to systemic therapy. Definition of biomarkers based on comprehensive characterization of CTCs has a strong potential to be translated to individualized targeted treatments and spare breast cancer patients unnecessary and ineffective therapies but also to reduce the costs for the health system and to downsize the extent and length of clinical studies. In this review, we briefly summarize recent studies on the molecular characterization of circulating tumor cells in breast cancer and discuss challenges and promises of CTCs for individualized cancer treatment.     

Biomarkers characterization of circulating tumour cells in breast cancer patients

Introduction

Increasing evidence supports the view that the detection of circulating tumor cells (CTCs) predicts outcomes of nonmetastatic breast cancer patients. CTCs differ genetically from the primary tumor and may contribute to variations in prognosis and response to therapy. As we start to understand more about the biology of CTCs, we can begin to address how best to treat this form of disease.

Methods

Ninety-eight nonmetastatic breast cancer patients were included in this study. CTCs were isolated by immunomagnetic techniques using magnetic beads labelled with a multi-CK-specific antibody (CK3-11D5) and CTC detection through immunocytochemical methods. Estrogen receptor, progesterone receptor and epidermal growth factor receptor (EGFR) were evaluated by immunofluorescence experiments and HER2 and TOP2A by fluorescence in situ hybridization. We aimed to characterize this set of biomarkers in CTCs and correlate it with clinical-pathological characteristics.

Results

Baseline detection rate was 46.9% ≥ 1 CTC/30 ml threshold. CTC-positive cells were more frequent in HER2-negative tumors (p = 0.046). In patients younger than 50 years old, HER2-amplified and G1-G2 tumors had a higher possibility of being nondetectable CTCs. Heterogeneous expression of hormonal receptors (HRs) in samples from the same patients was found. Discordances between HR expression, HER2 and TOP2A status in CTCs and their primary tumor were found in the sequential blood samples. Less that 35% of patients switched their CTC status after receiving chemotherapy. EGFR-positive CTCs were associated with Luminal tumors (p = 0.03).

Conclusions

This is the largest exploratory CTC biomarker analysis in nonmetastatic BC patients. Our study suggests that CTC biomarkers profiles might be useful as a surrogate marker for therapeutic selection and monitoring since heterogeneity of the biomarker distribution in CTCs and the lack of correlation with the primary tumor biomarker status were found. Further exploration of the association between EGFR-positive CTCs and Luminal tumors is warranted.     

Circulating Tumor Cells and Colorectal Cancer

The significance of circulating tumor cells (CTCs) has been discussed for more than a century. The advent of modern technology has allowed for more reliable detection of CTCs, and recent studies have provided compelling evidence that CTCs predict clinical response in metastatic colorectal cancer (mCRC). Combination of CTC analysis with independent prognostic factors has demonstrated powerful synergy in some studies. The ability of CTCs to predict metastasis and therapy-specific response has high potential clinical utility, with early studies showing promising results in colorectal cancer (CRC). Reliable CTC detection has also allowed for examination of tumor cell dissemination during surgery, and there appears to be a heavy dependence on the approach chosen. This review discusses the evidence for CTC significance, with particular focus on detection methods, novel markers, and clinical outcomes in CRC. Numerous opportunities exist for preclinical, clinical, and translational studies to explore molecular determinants within CTCs, as well as the value of CTCs in directing targeted therapeutics.     

循环肿瘤细胞在肺癌中的研究进展

循环肿瘤细胞(CTC)具有与肿瘤原发灶内一致的细胞学和基因遗传学特征。 已发现CTC与肺癌的生物学行为、治疗以及预后密切相关,有望成为肺癌的又一新标记物和治疗的新靶点。本文对CTC在肺癌中的研究进展作一综述。     

Clinical utility of circulating tumor cells: an update

The prognostic role of circulating tumor cells (CTCs) has been clearly demonstrated in many types of cancer. However, their roles in diagnostic and treatment strategies remain to be defined. In this review, we present an overview of the current clinical validity of CTCs in nonmetastatic and metastatic cancer, and the main studies or concepts investigating the clinical utility of CTCs. In particular, we focus on breast, lung, colorectal, and prostate cancer. Two major topics concerning the clinical utility of CTC are discussed: treatment based on CTC count or CTC variations, and treatment based on the molecular characteristics of CTCs. Although some of these studies are inconclusive, many are still ongoing, and their results could help to define the role of CTCs in the management of cancers. A summary of published or ongoing phase II‐III trials is also presented.     

乳腺癌循环肿瘤细胞研究进展与展望

目的:总结国内外乳腺癌循环肿瘤细胞(CTC)在检测手段及相关临床意义方面的研究进展,以及CTC检测项目在研究肿瘤转移过程中的地位、必要性及未来的发展方向.方法:应用Medline、PubMed及CNKI期刊全文数据库系统,以“乳腺癌、循环肿瘤细胞、转移、上皮间质转化”等为关键词,检索2006-06-2011-06的相关文献,共选择文献48篇加以分析总结.文献纳入标准:1)乳腺癌CTC的起源及其特点;2)乳腺癌CTC的检测方法;3)检测乳腺癌CTC的临床意义;4)乳腺癌CTC的特性.结果:CTC的检测在预测乳腺癌患者无病生存期和总生存期方面有重要价值;同时,它在预测和判断疗效方面优于一些传统方法.除此之外,CTC的分子学和生物学特性,如ER、PR、HER-2表达和上皮间质转化等,以及这些特性与乳腺癌转移的关系已成为新的研究热点.结论:对CTC的深入研究能够使我们进一步了解它,使其成为乳腺癌患者监测转移和预后的常规的检测指标,并有助于了解血行转移的机制,更有望发现乳腺癌治疗的新靶点.     

Review: circulating tumor cells in the practice of breast cancer oncology

The primary cause of tumor-related death in breast cancer is still represented by distant metastasization. The dissemination of tumor cells from the primary tumor to distant sites through bloodstream cannot be early detected by standard imaging methods. Circulating tumor cells (CTCs) play a major role in the metastatic spread of breast cancer. Different analytical systems for CTCs isolation and detection have been developed and novel areas of research are directed towards developing assays for CTCs molecular characterization. This review describes the current state of art on CTCs detection techniques and the present and future clinical implications of CTCs enumeration and characterization.     

循环肿瘤细胞检测技术的研究进展

循环肿瘤细胞（circulating tumor cells,CTCs）是导致发生肿瘤远处转移和复发的必要前提。随着靶向治疗的不断进步,对于无法取得肿瘤组织的晚期癌症患者,CTCs可作为一种肿瘤组织替代物指导患者治疗方案的选择。精确计数以及分子生物学分析对于肿瘤患者的预后判断、疗效评价以及个体化治疗均有重要的指导作用。随着CTCs检测技术不断发展,CTCs检测的准确性明显提高。本文针对CTCs的检测技术进行综述。      

Circulating tumour cells: their utility in cancer management and predicting outcomes

Recent advances in technology now permit robust and reproducible detection of circulating tumour cells (CTCs) from a simple blood test. Standardization in methodology has been instrumental in facilitating multicentre trials with the purpose of evaluating the clinical utility of CTCs. We review the current body of evidence supporting the prognostic value of CTC enumeration in breast, prostate and colorectal cancer, using standardized approaches, and studies evaluating the correlation of CTC number with radiological outcome. The exploitation of CTCs in cancer management, however, is now extending beyond prognostication. As technologies emerge to characterize CTCs at the molecular level, biological information can be obtained in real time, with the promise of serving as a 'surrogate tumour biopsy'. Current studies illuminate the potential of CTCs as pharmacodynamic and predictive biomarkers and potentially their use in revealing drug resistance in real time. Approaches for CTC characterization are summarized and the potential of CTCs in cancer patient management exemplified via the detection of epidermal growth factor receptor mutations from CTCs in patients with non-small cell lung cancer. The opportunity to learn more about the biology of metastasis through CTC analysis is now being realized with the horizon of CTC-guided development of novel anticancer therapies.     

CTC clusters in cancer progression and metastasis

Circulating tumor cells (CTC) in the blood of cancer patients are regarded as potential metastatic seeds, and their detailed characterization holds great promises for more exact prognosis, better diagnosis and therapy of the metastatic cancer. Circulating tumor cell clusters represent different class of CTCs, with specific properties, including high metastatic potential. In this review, we present current opinions on differences between single CTCs and CTC clusters, their mode of dissemination, methods of detection and clinical importance in various types of cancer.     

EpCAM-based Flow Cytometric Detection of Circulating Tumor Cells in Gallbladder Carcinoma Cases

Purpose: Liquid biopsy has entered the arena of cancer diagnostics in the past decade and detection of circulating tumor cells (CTC) is one diagnostic component. CTCs in gallbladder cancer (GBC) have hitherto not been comprehensively analysed. Methods and Results: The current study focused on the diagnostic role of CTCs in 27 cases of treatment-naive GBC and 6 normal controls as well as 6 cases of cholecystitis. An EasySep kit featuring negative immunomagnetic bead separation and flow cytometric detection of EpCAM positive and CD45 negative cells revealed CTCs in 25 of the 27 cases. At a cut-off point of ≥1, the CTC count discriminated GBC from controls with a sensitivity, specificity and diagnostic accuracy of 92.6%, 91.7% and 92.3%, respectively. CTC levels in turn correlated significantly with clinico-pathological parameters of cases in terms of known prognostic indicators, with significant diagnostic potential at a cut-off point of >4, to discriminate disease stage I and II vs. III and IV GBC. With a cut-off of >3, the CTC count discriminated tumor stages I and II vs. III and IV and at >6 CTCs could discriminate metastatic vs. non metastatic GBCs with a sensitivity, specificity and diagnostic accuracy of 55. 6%, 100.0% and 85.2, respectively. A review of CTC in pancreatico-biliary malignancies is included. Conclusion: Detection and quantification of CTCs may serve as a non-invasive biomarker for GBC diagnosis in correlation with radiological studies.