Circulating tumor cells: a useful predictor of treatment efficacy in metastatic breast cancer

Meta-analysis of the prognostic value of circulating tumor cells in breast cancer

PURPOSE

The prognostic value of circulating tumor cells (CTC) detected in breast cancer patients is currently under debate. Different time points of blood collections and various CTC assays have been used in the past decades. Here, we conducted the first comprehensive meta-analysis of published literature on the prognostic relevance of CTC, including patients with early and advanced disease.

EXPERIMENTAL DESIGN

A comprehensive search for articles published between January 1990 and January 2012 was conducted; reviews of each study were conducted and data were extracted. The main outcomes analyzed were overall survival (OS) and disease-free survival (DFS) in early-stage breast cancer patients, as well as progression-free survival (PFS) and OS in metastatic breast cancer patients. Pooled hazard ratio (HR) and 95% confidence intervals (CIs) were calculated using the random and the fixed-effects models. Subgroup and sensitivity analyses were also conducted.

RESULTS

Forty-nine eligible studies enrolling 6,825 patients were identified. The presence of CTC was significantly associated with shorter survival in the total population. The prognostic value of CTC was significant in both early (DFS: HR, 2.86; 95% CI, 2.19-3.75; OS: HR, 2.78; 95% CI, 2.22-3.48) and metastatic breast cancer (PFS: HR, 1.78; 95% CI, 1.52-2.09; OS: HR, 2.33; 95% CI, 2.09-2.60). Further subgroup analyses showed that our results were stable irrespective of the CTC detection method and time point of blood withdrawal.

CONCLUSION

Our present meta-analysis indicates that the detection of CTC is a stable prognosticator in patients with early-stage and metastatic breast cancer. Further studies are required to explore the clinical utility of CTC in breast cancer.

Clinical implications of the detection of circulating tumor cells in breast cancer patients

The detection of disseminated tumor cells in bone marrow is a common phenomenon seen in 30-40% of primary breast cancer patients. The presence of disseminated tumor cells at diagnosis as well as the persistence of disseminated tumor cells is strongly associated with poor clinical outcome. Since bone marrow biopsies are not well tolerated by many patients, the evaluation of circulating tumor cells in the blood might become a desired alternative. Circulating tumor cells are routinely detected, depending on stage of the disease and methodology, in 10-80% of breast cancer patients. Recent studies have shown a prognostic potential of circulating tumor cells in both primary and metastatic settings. The evaluation of circulating tumor cells may become one of the crucial markers for prediction of survival and therapy monitoring, and its characterization might enable specific targeting of minimal residual, and metastatic disease.

MUC1-positive circulating tumor cells and MUC1 protein predict chemotherapeutic efficacy in the treatment of metastatic breast cancer

Chemotherapy plays an important role in the treatment of metastatic breast cancer. It is important to monitor chemotherapeutic efficacy, to find a simple and efficient tool to guide treatment, and to predict the efficacy of treatment in a timely and accurate manner. This study aimed to detect mucin-1 (MUC1)– positive circulating tumor cells and MUC1 protein in the peripheral blood of patients with metastatic breast cancer and to investigate their relationship to chemotherapeutic efficacy. MUC1 mRNA was detected in the peripheral blood of 34 patients with newly diagnosed metastatic breast cancer by reverse transcription-polymerase chain reaction. The positive rates of MUC1 mRNA were 88.2% before chemotherapy and 70.6% after chemotherapy, without a significant difference (P = 0.564); MUC1 mRNA expression before chemotherapy had no correlation with treatment effectiveness (P = 0.281). The response rate of MUC1 mRNA-negative patients after first-cycle chemotherapy was significantly higher (P = 0.009) and the progression-free survival (PFS) was clearly longer than those of MUC1 mRNA-positive patients (P = 0.095). MUC1 protein in peripheral blood plasma was detected by an ELISA competitive inhibition assay. The patients with decreased MUC1 protein after chemotherapy had a significantly longer PFS than those with elevated MUC1 protein (P = 0.044). These results indicate that the outcomes of MUC1 mRNA-negative patients after chemotherapy are better than those of MUC1 mRNA-positive patients. In addition, patients with decreased expression of MUC1 protein have a better PFS.

Activity of pegylated liposomal doxorubicin in combination with gemcitabine in triple negative breast cancer with skin involvement: two case reports

Breast carcinoma (BC) is a heterogeneous disease in terms of histology, therapeutic response, dissemination patterns to distant sites and patient outcomes. Triple-negative breast cancer (TNBC), defined by the lack of protein expression of estrogen and progesterone receptors and the absence of HER2 protein overexpression (ER-/PR-/HER2-) has significant clinical implications due to their poor prognosis and the lack of targeted agents. Skin involvement is one of the most distressing presentations of locally recurrent breast cancer and few studies have identified effective agents in this setting. In fact, the increasing use of anthracycline/taxane-based chemotherapy in the neoadjuvant and/or adjuvant settings has led to investigate new cytotoxic therapies such as the combination of pegylated liposomal doxorubicin (PLD) with gemcitabine. Here, we report two cases of disseminated TNBC with extensive cutaneous metastases and a remarkable response to PLD in combination with gemcitabine. Further investigations are needed to confirm the efficacy of this regimen in skin involvement and TNBC.

Circulating tumor cells in immunohistochemical subtypes of metastatic breast cancer: lack of prediction in HER2-positive disease treated with targeted therapy

BACKGROUND

Circulating tumor cells (CTCs) are associated with inferior prognosis in metastatic breast cancer (MBC). We hypothesized that the relationship between CTCs and disease subtype would provide a better understanding of the clinical and biologic behavior of MBC.

PATIENTS AND METHODS

We retrospectively analyzed 517 MBC patients treated at a single institution. Subtypes of primary tumors were analyzed by immunohistochemical (IHC) or fluorescent in situ hybridization analyses and CTCs were enumerated by CellSearch(®) at starting a new therapy. Overall survival (OS) and progression-free survival durations for each IHC subtype were determined.

RESULTS

At a median follow-up of 24.6 months, 276 of 517 (53%) patients had died. The median OS for patients with <5 and ≥ 5 CTCs were 32.4 and 18.3 months, respectively (P < 0.001). Except in HER2+ patients, the prognostic value of CTCs was independent of disease subtype and disease site.

CONCLUSIONS

In this large retrospective study, CTCs were strongly predictive of survival in all MBC subtypes except HER2+ patients who had been treated with targeted therapy. Our results clearly demonstrate the value of enumerating CTCs in MBC and strongly suggest an interesting biological implication in the HER2+ subset of patients that need to be further explored.

Advances in understanding clinical significance of circulating tumor cells and cell-free DNA methylation in patients with hepatocellular carcinoma

During the early formation and growth of a primary tumor, tumor cells can be detached from the primary tumor and circulate through the bloodstream to form circulating tumor cells (CTCs). Also during the early stage of tumor development, apoptotic and necrotic tumor cells can release DNA into the bloodstream to form circulating cell-free DNA. Therefore, analysis of CTCs and circulating cell-free DNA is considered as a real-time "liquid biopsy" for cancer patients. CTCs are very heterogeneous and can be enriched and detected using different technologies based on their physical and biological properties. The use of modern molecular biological techniques to extract the cell-free DNA in circulating blood and detect aberrant genetic and epigenetic alterations can provide valuable information for the early diagnosis, prediction of response to therapy, recurrence monitoring and prognosis evaluation in cancer patients. In this paper, we will give a review of recent advances in understanding the clinical significance of CTCs and cell-free DNA in patients with hepatocellular carcinoma.

Epithelial mesenchymal transition: a new insight into the detection of circulating tumor cells

Many research groups reported on the relation between circulating tumor cells (CTCs) in peripheral blood and worse prognosis for metastatic cancer patients. These results are based on CTCs counting and did not take into account molecular characteristics of cells. To establish CTCs as a reliable and accurate biological marker, new technologies must be focused on CTC subpopulations: dedifferentiated circulating tumor cells (ddCTCs) arising from epithelial mesenchymal transition (EMT). To select and detect them, different methods have been proposed but none has still reached the goal. Technical progress and translational research are expected to establish CTCs as a real marker. Thus CTC evaluation profiling for each patient will lead to personalize followup and therapy.

Mesenchymal and stemness circulating tumor cells in early breast cancer diagnosis

Background

Epithelial mesenchymal transition (EMT) is a crucial event likely involved in dissemination of epithelial cancer cells. This process enables them to acquire migratory/invasive properties, contributing to tumor and metastatic spread. To know if this event is an early one in breast cancer, we developed a clinical trial. The aim of this protocol was to detect circulating tumor cells endowed with mesenchymal and/or stemness characteristics, at the time of initial diagnosis. Breast cancer patients (n = 61), without visceral or bone metastasis were enrolled and analysis of these dedifferentiated circulating tumor cells (ddCTC) was realized.

Methods

AdnaGen method was used for enrichment cell selection. Then, ddCTC were characterized by RT-PCR study of the following genes: PI3Kα, Akt-2, Twist1 (EMT markers) and ALDH1, Bmi1 and CD44 (stemness indicators).

Results

Among the studied primary breast cancer cohort, presence of ddCTC was detected in 39% of cases. This positivity is independant from tumor clinicopathological factors apart from the lymph node status.

Conclusions

Our data uniquely demonstrated that in vivo EMT occurs in the primary tumors and is associated with an enhanced ability of tumor cells to intravasate in the early phase of cancer disease. These results suggest that analysis of circulating tumor cells focused on cells showing mesenchymal or stemness characteristics might facilitate assessment of new drugs in clinical trials.

Identification and enumeration of circulating tumor cells in the cerebrospinal fluid of breast cancer patients with central nervous system metastases

The number of circulating tumor cells (CTCs) in the peripheral blood of metastatic breast cancer patients is now an established prognostic marker. While the central nervous system is a common site of metastasis in breast cancer, the standard marker for disease progression in this setting is cerebrospinal fluid (CSF) cytology. However, the significance of CSF cytology is unclear, requires large sample size, is insensitive and subjective, and sometimes yields equivocal results. Here, we report the detection of breast cancer cells in CSF using molecular markers by adapting the CellSearch system (Veridex). We used this platform to isolate and enumerate breast cancer cells in CSF of breast cancer patients with central nervous system (CNS) metastases. The number of CSF tumor cells correlated with tumor response to chemotherapy and were dynamically associated with disease burden. This CSF tumor cell detection method provides a semi-automated molecular analysis that vastly improves the sensitivity, reliability, objectivity, and accuracy of detecting CSF tumor cells compared to CSF cytology. CSF tumor cells may serve as a marker of disease progression and early-stage brain metastasis in breast cancer and potentiate further molecular analysis to elucidate the biology and significance of tumor cells in the CSF.

High independent prognostic and predictive value of circulating tumor cells compared with serum tumor markers in a large prospective trial in first-line chemotherapy for metastatic breast cancer patients

BACKGROUND

Circulating tumor cells (CTCs) are a prognostic marker in metastatic breast cancer, but comparisons with serum tumor markers (CA 15-3, carcinoembryonic antigen and lactate dehydrogenase) variations are needed.

PATIENTS AND METHODS

CTCs were counted with CellSearch® at baseline, before cycle 2 (C2) and cycle 3 or 4 (C3/4) in 267 metastatic breast cancer patients on first-line chemotherapy with/without targeted therapy.

RESULTS

Baseline CTC detection rate was 65% with ≥1 CTC/7.5 ml threshold and 44% with ≥5 CTC/7.5 ml and was independent of subtypes (luminal, triple negative, human epithelial growth factor receptor 2 (HER2)+). CTCs were associated with tumor markers, bone/liver involvement, tumor burden and performance status. CTC detection ≥1 CTC/7.5 ml was a strong prognostic factor for progression-free survival (PFS), P < 0.0001. Threshold of CTC ≥5 was statistically significant for PFS and overall survival (OS), P = 0.03 on multivariate analysis. Among patients with ≥5 CTC/7.5 ml at baseline, 50% had <5 CTC/7.5 ml at C2. Changes were correlated with both PFS and OS (P < 0.0001). All patients receiving anti-HER2 therapy had <5 CTC/7.5 ml after three cycles of treatment.

CONCLUSION

This is the largest prospective series validating the prognostic value of CTC independently from serum tumor marker. Elevated CTCs before C2 are an early predictive marker of poor PFS and OS, which could be used to monitor treatment benefit. CTC decrease under treatment seems stronger with targeted therapy.

Multimarker Analysis of Circulating Tumor Cells in Peripheral Blood of Metastatic Breast Cancer Patients: A Step Forward in Personalized Medicine

AIM: To develop an immunomagnetic assay for the isolation of circulating tumor cells (CTCs) followed by the analysis of a multimarker panel, which will enable the characterization of these malignant cells with high accuracy. PATIENTS AND METHODS: Peripheral blood (PB) was collected from 32 metastatic breast cancer patients and 42 negative controls. The antibodies BM7 and VU1D9 were used for immunomagnetic tumor cell enrichment. A real-time reverse transcription-polymerase chain reaction (RT-PCR) approach for the markers KRT19, SCGB2A2, MUC1, EPCAM, BIRC5 and ERBB2 was used for CTC detection and characterization. RESULTS: THE POSITIVITY RATES FOR EACH MARKER WERE AS FOLLOWS: 46.9% for KRT19, 25.0% for SCGB2A2, 28.1% for MUC1, 28.1% for EPCAM, 21.9% for BIRC5, and 15.6% for ERBB2. After the creation of individualized cutoffs, the sensitivity and specificity of the combined marker gene panel increased to 56.3% and 100%, respectively. Interestingly, 27.0% of the HER2-negative tumor patients showed ERBB2 mRNA-positive CTCs. CONCLUSIONS: The described technique can be used to measure CTCs with great accuracy. The use of a multimarker panel for the characterization of CTCs may provide real-time information and be of great value in therapy monitoring.

Concepts of metastasis in flux: the stromal progression model

The ability of tumor cells to leave a primary tumor, to disseminate through the body, and to ultimately seed new secondary tumors is universally agreed to be the basis for metastasis formation. An accurate description of the cellular and molecular mechanisms that underlie this multistep process would greatly facilitate the rational development of therapies that effectively allow metastatic disease to be controlled and treated. A number of disparate and sometimes conflicting hypotheses and models have been suggested to explain various aspects of the process, and no single concept explains the mechanism of metastasis in its entirety or encompasses all observations and experimental findings. The exciting progress made in metastasis research in recent years has refined existing ideas, as well as giving rise to new ones. In this review we survey some of the main theories that currently exist in the field, and show that significant convergence is emerging, allowing a synthesis of several models to give a more comprehensive overview of the process of metastasis. As a result we postulate a stromal progression model of metastasis. In this model, progressive modification of the tumor microenvironment is equally as important as genetic and epigenetic changes in tumor cells during primary tumor progression. Mutual regulatory interactions between stroma and tumor cells modify the stemness of the cells that drive tumor growth, in a manner that involves epithelial-mesenchymal and mesenchymal-epithelial-like transitions. Similar interactions need to be recapitulated at secondary sites for metastases to grow. Early disseminating tumor cells can progress at the secondary site in parallel to the primary tumor, both in terms of genetic changes, as well as progressive development of a metastatic stroma. Although this model brings together many ideas in the field, there remain nevertheless a number of major open questions, underscoring the need for further research to fully understand metastasis, and thereby identify new and effective ways of treating metastatic disease.

Conjunction of tumor cells with lymphocytes: implications for tumor invasion and metastasis

Our previous studies have led to a novel hypothesis that tumor metastasis is triggered by aberrant lymphocyte infiltration that disrupts intercellular junctions and surface adhesion molecules and causes dissociation of tumor cells from the primary tumor core, allowing lymphocytes to conjoin with dissociated tumor cells and physically 'drag' them to different tissue sites. Our hypothesis is supported by morphological and immunohistochemical data from multiple types of human cancer. This hypothesis challenges the traditional belief that the physical conjunction between tumor cells and lymphocytes would lead to degeneration of the tumor cells. To validate our hypothesis, H&E and immunostained sections were examined under high magnification to identify potential signs of degeneration-related changes. Our study revealed that >60% of isolated tumor cells overlying focal capsule disruptions, or within the stroma and vascular structures, were physically conjoined with lymphocytes to form tumor cell-lymphocyte chimeras (TLCs). Approximately 90% of the tumor cell partners of TLCs were morphologically indistinguishable from their counterparts within the tumor core. In addition, one third of the tumor cells of TLCs expressed high levels of cell proliferation specific proteins, or were undergoing mitosis. Our study also revealed that a subset of dilated lymphatic ducts or blood vessels at the site of focal capsule disruptions harbored variable numbers of tumor cells, and the wall of these structures was in direct physical continuity with the myoepithelial cell layer. Our study suggests that the onset of tumor metastasis may occur in two forms: (1) lymphocyte-mediated shuttling that allows lymphocytes to physically 'drag' tumor cells to different sites, and (2) tumor progenitor-mediated angiogenesis that allows tumor cells to directly enter the vascular structures.

Immunomagnetic separation technologies

The largest difficulty one faces in the development of technology for detection of circulating tumor cells (CTCs) is whether or not tumor cells are present in the blood and at what frequency. Although the introduction of the validated CellSearch system for CTC enumeration has facilitated CTC research the question remains whether CTC are missed or whether the CTC that are reported are indeed clinically relevant. To fulfill the promise of CTC as a real-time liquid biopsy they will need to be present in the blood volume tested and need to be isolated without losing the ability to test the presence of treatment targets. To characterize a sufficiently large number of CTCs in the majority of cancer patients the volume of blood needed is simply too large to process without enrichment prior to detection. Here, we review the detection of CTCs by flow cytometry and fluorescence microscopy with and without immunomagnetic enrichment.

CTCs in metastatic breast cancer

Circulating tumor cells (CTCs), enumerated by the Food and Drugs Administration-cleared CellSearch(®) system, are an independent prognostic factor of progression-free survival (PFS) and overall survival (OS) in metastatic breast cancer (MBC) patients. Several published papers demonstrated the poor prognosis for MBC patients who presented basal CTC count ≥5 in 7.5 mL of blood. Therefore, the enumeration of CTCs during treatment for MBC provides a tool with the ability to predict progression of disease earlier than standard timing of anatomical assessment using conventional radiological tests. Randomized clinical trials are ongoing to demonstrate whether CTCs detected by CellSearch(®) may help to guide treatments in MBC patients and improve prognosis. Moreover, the ability to perform molecular characterization of CTCs might identify a new druggable target in MBC patients. For example, the RT-PCR-based approach AdnaTest BreastCancerSelect(™) showed a high discordance rate in receptor expression between the primary tumors and CTCs. Theoretically, the phenotypic analysis of CTCs can represent a "liquid" biopsy of breast tumor that is able to identify a new potential target against the metastatic disease.

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 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.

Circulating tumor cells and circulating tumor DNA

Solid tumors derived from epithelial tissues (carcinomas) are responsible for 90% of all new cancers in Europe, and the main four tumor entities are breast, prostate, lung, and colon cancer. Present tumor staging is mainly based on local tumor extension, metastatic lymph node involvement, and evidence of overt distant metastasis obtained by imaging technologies. However, these staging procedures are not sensitive enough to detect early tumor cell dissemination as a key event in tumor progression. Many teams have therefore focused on the development of sensitive assays that allow the specific detection of single tumor cells or small amounts of cell-free tumor DNA in the peripheral blood of cancer patients. These methods allow the detection and characterization of early metastatic spread and will provide unique insights into the biology of metastatic progression of human tumors, including the effects of therapeutic interventions.

Clinical relevance and biology of circulating tumor cells

Most breast cancer patients die due to metastases, and the early onset of this multistep process is usually missed by current tumor staging modalities. Therefore, ultrasensitive techniques have been developed to enable the enrichment, detection, isolation and characterization of disseminated tumor cells in bone marrow and circulating tumor cells in the peripheral blood of cancer patients. There is increasing evidence that the presence of these cells is associated with an unfavorable prognosis related to metastatic progression in the bone and other organs. This review focuses on investigations regarding the biology and clinical relevance of circulating tumor cells in breast cancer.

Minimal residual disease and circulating tumor cells in breast cancer

Tumor cell dissemination in bone marrow or other organs is thought to represent an important step in the metastatic process. The detection of bone marrow disseminated tumor cells is associated with worse outcome in early breast cancer. Moreover, the detection of peripheral blood circulating tumor cells is an adverse prognostic factor in metastatic breast cancer, and emerging data suggest that this is also true for early disease. Beyond enumeration, the characterization of these cells has the potential to improve risk assessment, treatment selection and monitoring, and the development of novel therapeutic agents, and to advance our understanding of the biology of metastasis.

Determination of cut-offs for circulating tumor cell measurement in metastatic cancer

The metastatic transformation of epithelial tumors progresses through various steps leading to the generation of circulating tumor cells (CTCs). Measurement of CTCs in the peripheral blood is being increasingly recognized as a promising tool in breast oncology. Several studies have evaluated the prognostic significance of CTCs in newly diagnosed metastatic breast cancer (MBC) patients. The IC 2006-04 was a high-powered, prospective, multicenter, observational study conceived to assess CTC changes in women with MBC treated with first-line chemotherapy. Levels ≥ 5 CTCs/7.5 ml blood at baseline and before the second cycle of treatment were independent prognostic factors associated with shorter progression-free and overall survival. This study provides further level II evidence for the clinical and prognostic value of CTCs in MBC, confirming data from earlier small studies. It also provides proof that CTCs should be investigated in ongoing interventional trials to see if better patient outcomes can be attained by altering treatment based on CTC levels.

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.

Circulating tumor cells: advances in detection methods, biological issues, and clinical relevance

BACKGROUND

Circulating tumor cells (CTCs) have long been considered a reflection of tumor aggressiveness. Hematogenous spreading of CTCs from a primary tumor is a crucial step in the metastasis cascade, which leads ultimately to the formation of overt metastases. However, owing to the rarity of CTCs in peripheral blood, detecting these cells requires methods combined with high sensitivity and specificity, which sets tremendous challenges for the implementation of these assays into clinical routine.

METHODS

Generally, CTCs detection methods are composed of the following two steps: enrichment (isolation) process (morphological and immunological techniques) and detection (identification) process (cytometric and nucleic acid techniques), which may or may not be separate from enrichment. Genetic and molecular characterization of CTCs carried out by fluorescent in situ hybridization (FISH), comparative genomic hybridization (CGH), PCR-based techniques, and biomarker immunofluorescent staining extract more information about malignant profile, metastatic potential of CTCs, and the extent to which CTCs are genetically identical to the primary tumor.

RESULTS

Recent technical advances made it possible to detect CTCs. The efficacy of circulating tumor cell (CTC) detection among patients with solid malignancy has been investigated, which shows great potential to become a tool for real-time parameter of prognosis and serve as an early marker to assess the therapeutic response in overt cancers. Improvements in detection and characterization of CTCs will hopefully lead to refinement of clinical management of cancer patients.

CONCLUSION

This review addresses the majority of assays that have been published thus far, including the enrichment and detection steps and the markers used in these assays, accompanied by some biological issues of CTC and the results of clinical application harvested.

Circulating tumor cells as prognostic and predictive markers in metastatic breast cancer patients receiving first-line systemic treatment

Introduction

Circulating tumor cells (CTCs) represent an independent predictor of outcome in patients with metastatic breast cancer (MBC). We assessed the prognostic impact of CTCs according to different first-line systemic treatments, and explored their potential predictive value in MBC patients.

Methods

We retrospectively evaluated 235 newly diagnosed MBC patients, treated at the University of Texas MD Anderson Cancer Center. All patients had a baseline CTC assessment performed with CellSearch^®. Progression-free survival and overall survival were compared with the log-rank test between groups, according to CTC count (< 5 vs. ≥ 5) and type of systemic therapy. We further explored the predictive value of baseline CTCs in patients receiving different treatments.

Results

At a median follow-up of 18 months, the CTC count was confirmed to be a robust prognostic marker in the overall population (median progression-free survival 12.0 and 7.0 months for patients with CTC < 5 and ≥ 5, respectively; P < 0.001). Conversely, in patients with human epidermal growth factor receptor-2-overexpressed/amplified tumors receiving trastuzumab or lapatinib, the baseline CTC count was not prognostic (median progression-free survival 14.5 months for patients with CTC < 5 and 16.1 months for those with CTC ≥ 5; P = 0.947). Furthermore, in patients with human epidermal growth factor receptor-2 normal tumors, a baseline CTC count ≥ 5 identified subjects who derived benefit from more aggressive treatments, including combination chemotherapy and chemotherapy plus bevacizumab.

Conclusions

This analysis suggests that the prognostic information provided by CTC count may be useful in patient stratifications and therapeutic selection, particularly in the group with positive CTCs, in which various therapeutic choices may procure differential palliative benefit.

A novel approach using telomerase-specific replication-selective adenovirus for detection of circulating tumor cells in breast cancer patients

The aim of this study was to develop a new method for detecting circulating tumor cells (CTCs) in breast cancer patients by using the telomerase-specific replication-selective adenovirus OBP-401. Once transfected, OBP-401 can replicate only in telomerase expressing cells and emit fluorescence as it replicates so that the transfected cells become easily recognizable. Peripheral blood samples were drawn from 50 metastatic breast cancer patients and 27 early breast cancer patients. Blood samples were subjected to both the OBP-401 and CellSearch assays for the detection of CTCs and the results were compared. The recovery rate of the OBP-401 assay was one CTC in 7.5 ml blood combined with high specificity since no CTC was observed in 80 healthy controls. In 50 metastatic patients, 21 patients (42%) were identified as positive with the OBP-401 assay and 27 patients (54%) with the CellSearch assay. The CellSearch assay showed a significantly higher positivity for hormone receptor (HR)-positive tumors (estrogen receptor and/or progesterone receptor-positive tumors) (61%, 25/41, P = 0.012) or CA15-3-positive tumors (69%, 24/35, P = 0.003) than for HR-negative tumors (13%, 1/8) or CA15-3-negative tumors (21%, 3/14), respectively. Contrary, the OBP-401 assay results were similar regardless of their HR status (positive: 44% vs. negative: 38%, P = 0.738) or CA15-3 positivity (positive: 40% vs. negative: 50%, P = 0.523). Of the 27 early stage patients, four patients (15%) were identified by the OBP-401 assay and by the CellSearch assay, respectively, but there was no overlap in the CTCs-positive patients. In conclusion, the OBP-401 assay is comparable to the CellSearch assay in the detection rate of CTCs in both metastatic and early breast cancer patients. However, there was a great discrepancy in patients with CTCs between both assays. The OBP-401 assay may isolate CTCs with other biological characteristics which CTCs detected by the CellSearch assay do not have.

Circulating tumor cells and emerging blood biomarkers in breast cancer

PURPOSE OF REVIEW

To critically review the latest findings concerning the role of circulating tumor cells (CTCs) and other blood biomarkers in breast cancer.

RECENT FINDINGS

CTCs are epithelial tumor cells detected in the peripheral blood of patients with solid tumors using mainly cytometric/antibody-based and molecular approaches. Most technologies for CTC detection, including the FDA-approved CellSearch, are only detecting epithelial cell adhesion molecule (EpCAM)-positive CTCs and may miss clinically relevant subpopulations of CTCs. The value of CTC detection by CellSearch in metastatic breast cancer (MBC) may depend on the clinical setting and regimen used. In a retrospective analysis of 516 patients with MBC, CTC detection did not predict clinical outcome in chemo-naïve women with HER2-positive MBC treated with anti-HER2 therapy, but had prognostic value in other breast cancer subtypes. Similarly, changes in CTCs during treatment did not predict outcome in 67 women treated with first-line bevacizumab/chemotherapy. CTC detection by CellSearch before or after adjuvant chemotherapy was associated with worse disease-free survival in 1489 patients with early breast cancer. Circulating nucleic acids, microRNAs and genomic rearrangements have been suggested as promising blood biomarkers.

SUMMARY

Currently, there is no role for CTCs in clinical practice. The clinical utility of CTCs and other blood biomarkers should be prospectively tested.

Molecular mechanisms of metastasis in breast cancer--clinical applications

The metastatic cascade is a series of biological processes that enable the movement of tumor cells from the primary site to a distant location and the establishment of a new cancer growth. Circulating tumor cells (CTCs) have a crucial role in tumor dissemination. The role of CTCs in treatment failure and disease progression can be explained by their relation to biological processes, including the epithelial-to-mesenchymal transition and 'self seeding', defined as reinfiltration of the primary tumor or established metastasis by more aggressive CTCs. CTCs are a unique and heterogeneous cell population with established prognostic and predictive value in certain clinical situations. The possibility of collecting sequential blood samples for real-time monitoring of systemic-therapy efficacy presents new possibilities to evaluate targeted therapies based on the genomic profiling of CTCs and to improve the clinical management of patients by personalized therapy. Interruption of the metastatic cascade via the targeting of CTCs might be a promising therapeutic strategy.

Relevance of circulating tumor cells, extracellular nucleic acids, and exosomes in breast cancer

Early detection of cancer is vital to improved overall survival rates. At present, evidence is accumulating for the clinical value of detecting occult tumor cells in peripheral blood, plasma, and serum specimens from cancer patients. Both molecular and cellular approaches, which differ in sensitivity and specificity, have been used for such means. Circulating tumor cells and extracellular nucleic acids have been detected within blood, plasma, and sera of cancer patients. As the presence of malignant tumors are clinically determined and/or confirmed upon biopsy procurement-which in itself may have detrimental effects in terms of stimulating cancer progression/metastases-minimally invasive methods would be highly advantageous to the diagnosis and prognosis of breast cancer and the subsequent tailoring of targeted treatments for individuals, if reliable panels of biomarkers suitable for such an approach exist. Herein, we review the current advances made in the detection of such circulating tumor cells and nucleic acids, with particular emphasis on extracellular nucleic acids, specifically extracellular mRNAs and discuss their clinical relevance.

Using aptamers to visualize and capture cancer cells

Since diseased cells exist in exceedingly low concentration at the early stage of cancer, highly sensitive imaging and detection methods are required. By improving the methods for capturing and visualizing cancer cells, clinicians can diagnose metastatic relapse, stratify patients for therapeutic purposes, monitor response to drugs and therapies, and track tumor progression. Therefore, using advanced biotechnological and analytical methods combined with cell-SELEX (systematic evolution of ligands by exponential enrichment)-based aptamers, we improved the capture and visualization of diseased cells in a manner that is inexpensive, simple, sensitive, and fast. This multiplexed cancer detection platform therefore improves our control over a range of clinical exigencies, including cancer diagnosis, therapeutic modalities, and drug delivery systems.

Circulating tumor cells

Circulating tumor cells (CTCs) can be separated and characterized from normal hematopoietic cellular constituents by a variety of methods. Different strategies have included separation by physical characteristics, such as size or weight, or by biological characteristics, such as expression of epithelial or cancer-specific markers. Of the latter, rtPCR for epithelial-related gene message, such as cytokeratin, and immunoseparation techniques using monoclonal antibodies against epithelial cellular adhesion molecule, have gained the most widespread use in investigational and standard clinical application to date. Detection and monitoring of CTCs might be useful for screening, prognosis, prediction of response to therapy, or monitoring clinical course in patients with primary or metastatic cancer. Currently, monitoring patients with metastatic disease is the most practical application of CTCs. In this regard, several studies have demonstrated that approximately 50-70% of patients with metastatic breast, colon, and prostate cancers have elevated CTC levels, when evaluated using a highly automated immunomagnetic CTC assay system, designated CellSearch®. These studies demonstrate that elevated CTC levels prior to initiation of a new systemic therapy are associated with a worse prognosis than those that do not, and that persistently elevated or subsequent rising CTC levels strongly suggest that the therapeutic regimen with which the patient is being treated is not working. Similar results have been shown with rtPCR assays, although they are not as widely available for routine clinical use. New areas of research are directed toward developing more sensitive means of CTC detection and generating a variety of methods to characterize the molecular and biologic nature of CTCs, such as the status of hormone receptors, epidermal, and other growth factor receptor family members, and indications of stem-cell characteristics.