Detection of circulating tumor cells and tumor stem cells in patients with breast cancer by using flow cytometry: a valuable tool for diagnosis and prognosis evaluation. Tumour Biol. 2012;33:561-569. [PMID: 22241087 DOI: 10.1007/s13277-011-0303-1]

Detection of circulating tumor cells that predicts the efficacy of neoadjuvant chemotherapy for locally advanced triple-negative breast cancer

Objective

This study aims to assess the predictive potential of circulating tumor cells (CTCs) and circulating tumor stem cells (CTSCs) in locally advanced triple-negative breast cancer (TNBC) undergoing neoadjuvant chemotherapy (NAC) compared to the RECIST 1.1 standard.

Methods

We analyzed 112 patients with TNBC at the Liaoning Tumor Hospital. CTCs and CTSCs were evaluated before NAC, on the first NAC cycle day, and after NAC. We assessed the ability of positive CTSCs after the first cycle to predict NAC resistance (requiring regimen change) with a 91% specificity. Additionally, we analyzed CTC dynamics during the first NAC cycle to predict efficacy (often reaching MP4 or MP5) with 87% sensitivity and 80% specificity.

Results

Positive CTSCs post-first cycle predicted NAC resistance with high specificity (91%). The gradual decline in CTCs during the first NAC cycle indicated NAC efficacy, allowing the regimen to continue with a sensitivity of 87% and specificity of 80%.

Conclusion

This study suggests that positive CTSCs after the first NAC cycle predict resistance, thereby facilitating early detection (≥ 6 weeks earlier than RECIST). Gradual CTC reduction during the first cycle predicts efficacy, enabling regimen continuation. CTCs and CTSCs show promise as predictive markers for NAC efficacy in patients with locally advanced TNBC.

Nanomaterial-based detection of circulating tumor cells and circulating cancer stem cells for cancer immunotherapy

Nanomaterials have emerged as transformative tools for detecting circulating tumor cells (CTCs) and circulating cancer stem cells (CCSCs), significantly enhancing cancer diagnostics and immunotherapy. Nanomaterials, including those composed of gold, magnetic materials, and silica, have enhanced the sensitivity, specificity, and efficiency of isolating these rare cells from blood. These developments are of paramount importance for the early detection of cancer and for providing real-time insights into metastasis and treatment resistance, which are essential for the development of personalized immunotherapies. The combination of nanomaterial-based platforms with phenotyping techniques, such as Raman spectroscopy and microfluidics, enables researchers to enhance immunotherapy protocols targeting specific CTC and CCSC markers. Nanomaterials also facilitate the targeted delivery of immunotherapeutic agents, including immune checkpoint inhibitors and therapeutic antibodies, directly to tumor cells. This synergistic approach has the potential to enhance therapeutic efficacy and mitigate the risk of metastasis and relapse. In conclusion, this review critically examines the use of nanomaterial-driven detection systems for detecting CTCs and CCSCs, their application in immunotherapy, and suggests future directions, highlighting their potential to transform the integration of diagnostics and treatment, thereby paving the way for more precise and personalized cancer therapies.

Beyond the barrier: the immune-inspired pathways of tumor extravasation

Extravasation is a fundamental step in the metastatic journey, where cancer cells exit the bloodstream and breach the endothelial cell barrier to infiltrate target tissues. The tactics cancer cells employ are sophisticated, closely reflecting those used by the immune system for tissue surveillance. Remarkably, tumor cells have been observed to form distinct associations or clusters with immune cells where neutrophils stand out as particularly crucial partners. These interactions are not accidental; they are critical for cancer cells to exploit the immune functions of neutrophils and successfully extravasate. In another strategy, tumor cells mimic the behavior and characteristics of immune cells. They release a suite of inflammatory mediators, which under normal circumstances, guide the processes of endothelium reshaping and facilitate the entry and movement of immune cells within tissues. In this review, we offer a new perspective on the tactics employed by cancer cells to extravasate and infiltrate target tissues. We delve into the myriad mechanisms that tumor cells borrow, adapt, and refine from the immune playbook. Video Abstract.

Ultrahigh-Throughput, Real-Time Flow Cytometry for Rare Cell Quantification from Whole Blood

We present an ultrahigh-throughput, real-time fluorescence cytometer comprising a viscoelastic microfluidic system and a complementary metal-oxide-semiconductor (CMOS) linear image sensor-based detection system. The flow cytometer allows for real-time quantification of a variety of fluorescence species, including micrometer-sized particles and cells, at analytical throughputs in excess of 400,000 species per second. The platform integrates a custom C++ control program and graphical user interface (GUI) to allow for the processing of raw signals, adjustment of processing parameters, and display of fluorescence intensity histograms in real time. To demonstrate the efficacy of the platform for rare event detection and its utility as a basic clinical tool, we measure and quantify patient-derived circulating tumor cells (CTCs) in peripheral blood, realizing that detection has a sensitivity of 6 CTCs per million blood cells (0.000006%) with a volumetric throughput of over 3 mL/min.

Circulating CD45+EpCAM+ cells as a diagnostic marker for early-stage primary lung cancer

Lung cancer is a highly prevalent type of cancer, accounting for 11.6% of all cancer incidences. Early detection and treatment can significantly improve the survival rate and quality of life of patients; however, there is no accurate, effective, and easy-to-use test for early lung cancer screening. In this study, flow cytometry was used to detect the presence of CD45+EpCAM+ cells in tumor tissues and peripheral blood mononuclear cells (PBMCs) in patients with lung cancer. Moreover, the proportion of CD45+EpCAM+ cells in PBMCs of patients with lung cancer was found to be significantly higher than that of healthy volunteers. Tumor-related serum markers level was also measured in the peripheral blood of these patients using an electrochemiluminescence assay. The correlation between CD45+EpCAM+ cells, carcinoembryonic antigen (CEA), and lung cancer was investigated using receiver operating characteristic (ROC) curve analysis, which showed the sensitivity and specificity of the CD45+EpCAM+ cell to be 81.58% and 88.89%, respectively. Further analysis yielded an area under the ROC curve (ROC/area under the curve [AUC]) of 0.845 in patients PBMCs with lung cancer, which was slightly higher than that of CEA (0.732). Therefore, the detection of CD45+EpCAM+ cells in PBMCs may be helpful for the early screening and auxiliary diagnosis of lung cancer.

Detection and Characterization of Circulating Tumor Cells Using Imaging Flow Cytometry—A Perspective Study

Simple Summary

Liquid biopsy is non-invasive approach used to prognose and monitor tumor progression based on the detection and examination of metastasis-related events found in the patients’ blood (such as circulating tumor cells (CTCs), extracellular vesicles, and circulating nucleic acids). Different ultrasensitive techniques are applied to study those events and the biology of tumor dissemination, which in the future might complement standard diagnostics. Here, we suggest that CTCs analysis could be improved by the usage of imaging flow cytometry, combining advantages of both standard flow cytometry (high-scale analysis) and microscopy (high resolution) to investigate detailed features of those cells. From this perspective, we discuss the potential of this technology in the CTC field and present representative images of CTCs from breast and prostate cancer patients analyzed with this method.

Abstract

Tumor dissemination is one of the most-investigated steps of tumor progression, which in recent decades led to the rapid development of liquid biopsy aiming to analyze circulating tumor cells (CTCs), extracellular vesicles (EVs), and circulating nucleic acids in order to precisely diagnose and monitor cancer patients. Flow cytometry was considered as a method to detect CTCs; however, due to the lack of verification of the investigated cells’ identity, this method failed to reach clinical utility. Meanwhile, imaging flow cytometry combining the sensitivity and high throughput of flow cytometry and image-based detailed analysis through a high-resolution microscope might open a new avenue in CTC technologies and provide an open-platform system alternative to CellSearch^®, which is still the only gold standard in this field. Hereby, we shortly review the studies on the usage of flow cytometry in CTC identification and present our own representative images of CTCs envisioned by imaging flow cytometry providing rationale that this novel technology might be a good tool for studying tumor dissemination, and, if combined with a high CTC yield enrichment method, could upgrade CTC-based diagnostics.

Effects of salinomycin and niclosamide on small cell lung cancer and small cell lung cancer circulating tumor cell lines

Tumor dissemination and recurrence is attributed to highly resistant cancer stem cells (CSCs) which may constitute a fraction of circulating tumor cells (CTCs). Small cell lung cancer (SCLC) constitutes a suitable model to investigate the relation of CTCs and CSCs due to rapid tumor spread and a high number of CTCs. Expansion of five SCLC CTC lines (BHGc7, 10, 16, 26 and UHGc5) in vitro at our institution allowed for the analysis of CSC markers and cytotoxicity of the CSC-selective drugs salinomycin and niclosamide against CTC single cell suspensions or CTC spheroids/ tumorospheres (TOS). Salinomycin exerted dose-dependent cytotoxicity against the SCLC lines but, with exception of BHGc7 TOS, there was no markedly enhanced activity against TOS. Similarly, niclosamide exhibits high activity against BHGc7 TOS and UHGc5 TOS but not against the other CTC spheroids. High expression of the CSC marker CD133 was restricted to three SCLC tumor lines and the BHGc10 CTC line. All SCLC CTCs are CD24-positive but lack expression of CD44 and ABCG2 in contrast to the SCLC tumor lines which show a phenotype more similar to that of CSCs. The stem cell marker SOX2 was found in all CTC lines and SCLC GLC14/16, whereas elevated expression of Oct-3/4 and Nanog was restricted to BHGc26 and UHGc5. In conclusion, the SCLC CTCs established from patients with relapsed disease lack a typical CSC phenotype in respect to chemosensitivity to CSC-selective drugs, surface markers, expression of pluripotent stem cell and transcription factors.

Clinical significance of circulating tumor cells and tumor markers in the diagnosis of lung cancer

Background

Lung cancer has the highest fatality rate of all cancer types. To improve patients’ survival and life quality, it is therefore very important to screen for and detect it at an early stage.

Methods

A negative enrichment–fluorescence in situ hybridization (NE‐FISH) approach was used to detect circulating tumor cells (CTCs) in lung cancer patients, and levels of lung cancer‐associated serum markers were also measured in the peripheral blood of these same patients. The correlation between CTCs, serum cancer markers (carcinoembryonic antigen [CEA], CA 125, CYFRA 21‐1, and SCC), and clinicopathological characteristics was then investigated. Moreover, the potential clinical use of the combination of CTCs and tumor markers for the diagnosis of lung cancer, especially at early stages, was also explored.

Results

CTC frequencies in lung cancer patients were significantly higher than in healthy control volunteers or patients with benign lung disease, and the area under the receiver operating characteristics curve for the control group was 0.846 (95% CI 0.796‐0.887, P < 0.001). The rate of CTC positivity in lung cancer patients was 68.29% when the CTC cutoff value was 2, and the sensitivity of this means of lung cancer detection rose to 82.93% by combining CTC‐based detection with measurements of serum tumor markers. Similarly, the diagnostic sensitivity of this approach in early‐stage lung cancer patients (I‐II) was improved from 63.93% to 78.69%. Detection of CTCs can thus assist with the identification of benign and malignant pulmonary nodules.

Conclusions

It is potentially helpful and effective to employ a combination of CTCs and serum tumor markers for the clinical diagnosis of lung cancer.

Heterogeneity in Circulating Tumor Cells: The Relevance of the Stem-Cell Subset

The release of circulating tumor cells (CTCs) into vasculature is an early event in the metastatic process. The analysis of CTCs in patients has recently received widespread attention because of its clinical implications, particularly for precision medicine. Accumulated evidence documents a large heterogeneity in CTCs across patients. Currently, the most accepted view is that tumor cells with an intermediate phenotype between epithelial and mesenchymal have the highest plasticity. Indeed, the existence of a meta-stable or partial epithelial–mesenchymal transition (EMT) cell state, with both epithelial and mesenchymal features, can be easily reconciled with the concept of a highly plastic stem-like state. A close connection between EMT and cancer stem cells (CSC) traits, with enhanced metastatic competence and drug resistance, has also been described. Accordingly, a subset of CTCs consisting of CSC, present a stemness profile, are able to survive chemotherapy, and generate metastases after xenotransplantation in immunodeficient mice. In the present review, we discuss the current evidence connecting CTCs, EMT, and stemness. An improved understanding of the CTC/EMT/CSC connections may uncover novel therapeutic targets, irrespective of the tumor type, since most cancers seem to harbor a pool of CSCs, and disclose important mechanisms underlying tumorigenicity.

Circulating Tumor Cells: Strategies for Capture, Analyses, and Propagation

Circulating tumor cells (CTCs) play a central role in tumor dissemination and metastases, which are ultimately responsible for most cancer deaths. Technologies that allow for identification and enumeration of rare CTC from cancer patients' blood have already established CTC as an important clinical biomarker for cancer diagnosis and prognosis. Indeed, current efforts to robustly characterize CTC as well as the associated cells of the tumor microenvironment such as circulating cancer associated fibroblasts (cCAF), are poised to unmask key insights into the metastatic process. Ultimately, the clinical utility of CTC will be fully realized once CTC can be reliably cultured and proliferated as a biospecimen for precision management of cancer patients, and for discovery of novel therapeutics. In this review, we highlight the latest CTC capture and analyses technologies, and discuss in vitro strategies for culturing and propagating CTC.

Clinical significance of circulating tumor cells in gastric cancer patients

Circulating tumor cells (CTCs) are rare cancer cells released from tumors into the blood stream that are thought to have a key role in cancer metastasis. Investigation of CTCs is an exciting area of research but remains in its infancy, and the presence of CTCs has been associated with worse prognosis in several major cancer types. Gastric cancer (GC) is a highly lethal malignancy and a serious public health concern in East Asia especially in China. There is an urgent need for identifying new, better prognostic markers to enhance diagnosis and prognosis, facilitate drug development, and to improve the treatment of gastric cancer patients. There are considerable interests in gastric CTCs given their potential use as gastric cancer biomarkers. This review highlights recent advances in studies of gastric CTCs, including the isolation and biological molecular characteristics of gastric CTCs, and their clinical significance.

Circulating Tumor Cells Detected by the Expression of Cancer Stem Cell Markers CD90 and CD44 in Patients With Esophageal Cancer

Background

Epithelial cell adhesion molecule (EpCAM) is a marker for circulating tumor cells (CTCs) in various types of cancer. Cell surface antigens, such as CD90 and CD44, have been reported to be cancer stem cell (CSC) markers in esophageal squamous cell carcinoma (ESCC). The aim of this study was to assess the use of CD90 and CD44 as markers to identify clinically significant CTC subpopulations in ESCC.

Methods

We collected 3 mL of peripheral blood from 10 ESCC patients and 10 healthy volunteers to detect combined expression of EpCAM, CD90, and CD40 using flow cytometry.

Results

The number of EpCAM-positive cell counts (average ± SD) in the patients was significantly higher than healthy volunteers (29.1 ± 35.9 and 2.3 ± 2.5, P = 0.001). The proportions (average ±SD) of CD90- and CD44-positive cells in EpCAM-positive cells were 45.7% ± 42.4% and 98.7% ± 2.7%, respectively. EpCAM-positive/CD44-positive CTC counts, which was equivalent to EpCAM-positive CTC counts, correlated with pathologic V factors in the resected primary tumors (P &gt; 0.01). EpCAM-positive/CD90-positive CTC counts, but not EpCAM-positive/CD90-negative CTC counts, correlated with pathologic V factors in the resected primary tumors (P = 0.01). Our results suggested that combined expression of EpCAM and CD90 may useful to detect CTC subsets, which have highly metastatic features in ESCC. CD44, on the other hand, is equivalent to EpCAM as a marker to detect CTCs in ESCC.

Current approaches for avoiding the limitations of circulating tumor cells detection methods-implications for diagnosis and treatment of patients with solid tumors

Eight million people die of cancer each year and 90% of deaths are caused by systemic disease. Circulating tumor cells (CTCs) contribute to the formation of metastases and thus are the subject of extensive research and an abiding interest to biotechnology and pharmaceutical companies. Recent technological advances have resulted in greatly improved CTC detection, enumeration, expansion, and culture methods. However, despite the fact that nearly 150 years have passed since the first detection and description of CTCs in human blood and enormous technological progress that has taken place in this field, especially within the last decade, few CTC detection methods have been approved for routine clinical use. This reflects the substantial methodological problems related to the nature of these cells, their heterogeneity, and diverse metastatic potential. Here, we provide an overview of CTC phenotypes, including the plasticity of CTCs and the relevance of inflammation and cell fusion phenomena for CTC biology. We also review the literature on CTC detection methodology-its recent improvements, clinical significance, and efforts of its clinical application in cancer patients management. At present, CTC detection remains a challenging diagnostic approach as a result of numerous current methodological limitations. This is especially problematic during the early stages of the disease due to the small numbers of CTCs released into the blood of cancer patients. Nonetheless, the rapid development of novel techniques of CTC detection and enumeration in peripheral blood is expected to expedite their implementation in the clinical setting. It is of utmost importance to understand the biology of CTCs and their distinct populations as a prerequisite for achieving this ultimate goal.

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.

Molecular characterization of CD44+/CD24-/Ck+/CD45- cells in benign and malignant breast lesions

Breast cancer epithelial cells with the CD44⁺/CD24^-/low phenotype possess tumor-initiating cells and epithelial-mesenchymal transition (EMT) capacity. Massive parallel sequencing can be an interesting approach to deepen the molecular characterization of these cells. We characterized CD44⁺/CD24^-/cytokeratin(Ck)⁺/CD45^- cells isolated through flow cytometry from 43 biopsy and 6 mastectomy samples harboring different benign and malignant breast lesions. The Ion Torrent Ampliseq Cancer Hotspot panel v2 (CHPv2) was used for the identification of somatic mutations in the DNA extracted from isolated CD44⁺/CD24^-/Ck⁺/CD45^- cells. E-Cadherin and vimentin immunohistochemistry was performed on sections from the corresponding formalin-fixed, paraffin-embedded (FFPE) blocks. The percentage of CD44⁺/CD24^-/Ck⁺/CD45^- cells increased significantly from non-malignant to malignant lesions and in association with a significant increase in the expression of vimentin. Non-malignant lesions harbored only a single-nucleotide polymorphism (SNP). Mutations in the tumor suppressor p53 (TP53), NOTCH homolog 1 (NOTCH1), phosphatase and tensin homolog (PTEN), and v-akt murine thymoma viral oncogene homolog 1 (AKT1) genes were found in isolated CD44⁺/CD24^-/Ck⁺/CD45^- cells from ductal carcinomas in situ (DCIS). Additional mutations in the colony-stimulating factor 1 receptor (CSF1R), ret proto-oncogene (RET), and TP53 genes were also identified in invasive ductal carcinomas (IDCs). The use of massive parallel sequencing technology for this type of application revealed to be extremely effective even when using small amounts of DNA extracted from a low number of cells. Additional studies are now required using larger cohorts to design an appropriate mutational profile for this phenotype.

Circulating tumor cells expressing cancer stem cell marker CD44 as a diagnostic biomarker in patients with gastric cancer

Epithelial cell adhesion molecule (EpCAM) is a marker for circulating tumor cells (CTCs) in various types of cancer, while cluster of differentiation 44 (CD44) is a marker for gastric cancer (GC) stem cells. To evaluate the clinical significance of CD44⁺ CTCs in patients with GC in the present study, the number of EpCAM⁺CD44⁺ and EpCAM⁺CD44^- cells were detected in the peripheral blood of 26 GC patients and 12 healthy volunteers using flow cytometry. The number (mean ± standard deviation) of EpCAM⁺CD44⁺ cells in the GC patients and healthy volunteers was 69.9±52.0 and 0.91±2.10, respectively (P=0.0001), while that of EpCAM⁺CD44^- cells was 59.1±88.0 and 9.83±9.91, respectively (P=0.0313). The sensitivity and specificity of EpCAM⁺CD44⁺ cell detection for the identification of GC patients were 92.3 and 100%, respectively. By contrast, the values of EpCAM⁺CD44^- cell detection were 76.9 and 83.3%, respectively. The number of EpCAM⁺CD44⁺ cells in the GC patients was correlated with the disease stage (P=0.0423), the depth of the tumor (P=0.0314) and venous invasion (P=0.0184) in the resected tumor specimens, while the number of EpCAM⁺CD44^- cells did not correlate with any clinicopathological factors. The number of EpCAM⁺CD44⁺ cells significantly decreased following surgical resection of the tumor or induction of systemic chemotherapy. Additionally, atypical cells with a high nuclear to cytoplasmic ratio were morphologically detected in the sorted EpCAM⁺CD44⁺ cells. These results suggested that CD44⁺ CTCs, but not CD44^- CTCs, reflect the malignant status of the primary tumor in patients with GC, providing a candidate biomarker for diagnosis and treatment response.

Detection of circulating tumor cells by p75NTR expression in patients with esophageal cancer

Background

The p75 neurotrophin receptor (p75NTR) is a cancer stem cell (CSC) marker in esophageal squamous cell carcinoma (ESCC). This study aimed to assess the use of p75NTR in detecting circulating tumor cells (CTCs) in ESCC.

Methods

Peripheral blood mononuclear cell expression of epithelial cell adhesion molecule (EpCAM) and p75NTR was detected in 23 ESCC patients (13 received chemo- or chemoradiotherapy and 10 received curative surgery) and 10 healthy controls by flow cytometry.

Results

EpCAM + p75NTR+ cell counts (average ± SD) were significantly higher in patients (n = 23, 16.0 ± 18.3) compared to controls (n = 10, 0.4 ± 0.9, p = 0.013). The sensitivity and specificity to differentiate ESCC patients from controls were 78.3 and 100 % (cut-off value 4.0), respectively. EpCAM + p75NTR+, but not EpCAM + p75NTR− cell counts, correlated with clinically diagnosed distant metastasis (n = 13, p = 0.006) and pathological venous invasion in resected primary tumors (n = 10, p = 0.016). Malignant cytology was microscopically confirmed in isolated EpCAM + p75NTR+ cells with immunocytochemical double staining.

Conclusions

p75NTR is suggested to be a useful marker for clinically significant CTCs, which exhibit highly metastatic features in ESCC.

Circulating Tumor Cells and Cancer Stem Cells: Clinical Implications in Nonmetastatic Breast Cancer

Purpose

Despite the therapeutic advances, disease recurrence remains an ever-present threat to the health and well-being of breast cancer survivors. Assessment of circulating tumor cells (CTCs) and cancer stem cells (CSCs) during and after treatment may be of value in refining treatment.

Methods

Three 5 mL blood samples were taken from each patient: the first, at diagnosis; the second, after completion of neoadjuvant anthracyclin-based chemotherapy; and the third, a month after surgery and completion of adjuvant radiotherapy. The absolute numbers of CTCs were identified as CD45-cytokeratin+ cells. CTCs per 5 mL of blood were determined by recording all events in the whole suspension. CSCs were identified as cytokeratin⁺CD44⁺CD24-/CD45- cells. The CSCs were expressed as a percentage of CTCs.

Results

Univariate analysis identified the measurements of baseline CTCs and CSCs, taken after chemotherapy and one month after the cessation of radiotherapy, as prognostic factors for both four-year disease-free survival and four-year overall survival. Multivariable analysis identified the third measurement of CSCs, taken one month after the completion of radiotherapy, as the only independent prognostic factor for the four-year disease-free survival (P < 0.002, hazard ratio [HR] = 1.231, 95% CI 1.077–1.407). The initial CTC measurement was the one factor that reached significance on multivariate analysis (P < 0.03, HR 1.969, 95% CI 1.092–3.551) for the four-year overall survival. Correlation was higher between CTC and CSC counts at diagnosis (r = 0.654, P < 0.001) than after chemotherapy (r = 0.317, P < 0.03), because of the more rapid decrease in the mean CTC count with chemotherapy.

Conclusion

The CTC count could be suitable as one of the measures for monitoring response to chemotherapy, while persistence of CSC after cessation of the treatment of nonmetastatic breast cancer, except hormonal therapy when indicated, may be a reason to consider additional therapy in the future. These findings need confirmation in larger randomized trials.

Clinical implications of circulating tumor cells of breast cancer patients: role of epithelial-mesenchymal plasticity

There is increasing interest in circulating tumor cells (CTCs) due to their purported role in breast cancer metastasis, and their potential as a “liquid biopsy” tool in breast cancer diagnosis and management. There are, however, questions with regards to the reliability and consistency of CTC detection and to the relationship between CTCs and prognosis, which is limiting their clinical utility. There is increasing acceptance that the ability of CTCs to alter from an epithelial to mesenchymal phenotype plays an important role in determining the metastatic potential of these cells. This review examines the phenotypic and genetic variation, which has been reported within CTC populations. Importantly, we discuss how the detection and characterization of CTCs provides additional and often differing information from that obtained from the primary tumor, and how this may be utilized in determining prognosis and treatment options. It has been shown for example that hormone receptor status often differs between the primary tumor and CTCs, which may help to explain failure of endocrine treatment. We examine how CTC status may introduce alternative treatment options and also how they may be used to monitor treatment. Finally, we discuss the most interesting current clinical trials involving CTC analysis and note further research that is required before the breast cancer “liquid biopsy” can be realized.

Flow cytometric analysis of CD133- and EpCAM-positive cells in the peripheral blood of patients with lung cancer

Lung tumors are characterized by their high metastatic potential, which is the main cause of therapeutic failure. However, the exact cellular origin of metastasis remains unknown. Since the introduction of the cancer stem cell theory, lung cancer stem cells (LCSCs) have been thought to represent metastasis-founding cells. The current study aimed to evaluate whether LCSCs could be found in the circulation. Expression of the stem cell markers CD133 and EpCAM was confirmed in tumor and normal lung tissue by flow cytometry. Then, this technique was further used to investigate the expression of CD133 and EpCAM in the peripheral blood of 41 patients with primary lung cancer. Putative LCSCs (CD133?EpCAM?) were present in 6/7 tumor samples, and CD133?EpCAM? cells were identified in the blood samples of 15 patients at a median level of 40/ml of blood. EpCAM? cells were detected in 60 % of the patients, and the number of these cells was higher in patients with adenocarcinoma than patients with squamous cell carcinoma and was also higher in patients with less advanced disease. Moreover, the frequency of this subpopulation significantly correlated with the circulating level of SSEA-4? cells. Additionally, CD133?EpCAM- cells were found in 87 % of the patients, and the numbers of these cells were significantly higher in patients with distant metastases and correlated with disease stage. This study confirmed the presence of an LCSC subpopulation with a CD133?EpCAM? phenotype in the tumors and blood of patients with lung cancer, and these results suggest an important role for CD133 and EpCAM in lung cancer progression and their potential application as novel biomarkers of the disease.

Stem cell-like circulating tumor cells indicate poor prognosis in gastric cancer

Circulating tumor cells (CTCs), which have stem cell-like characteristics, might play a crucial role in cancer metastasis. CD44 has been identified as gastric cancer (GC) stem cell (CSC) marker. Here, the prognostic significance of CD44-positive CTCs in GC patients was investigated. CTCs were detected in 27 of 45 GC patients. The presence of CTCs was significantly associated with lymph node metastasis, distant metastasis, and recurrence (P = 0.007, P = 0.035, and P = 0.035, resp.). Nineteen of the 27 CTC-positive patients had CD44-positive CTCs. These patients were more likely to develop metastasis and recurrence than patients with CD44-negative CTCs. CD44-positive CTC counts were higher in recurrent patients than in the nonrecurrent ones (means 4.8 and 1.9, resp.; P = 0.010). Furthermore, 13 of 19 patients with CD44-positive CTCs developed recurrent disease, and the mean time to recurrence was shorter than that in patients with CD44-negative CTCs (10.54 ± 5.55 and 19.13 ± 9.72 months, resp.; P = 0.04). COX proportional hazards model indicated that the presence of CD44-positive CTCs and TNM stage were independent predictors of recurrence for GC (P = 0.030 and 0.008). So identifying the stem cell-like CTC subset may provide more clinically useful prognostic information than only detecting CTCs.

Curcumin targets breast cancer stem-like cells with microtentacles that persist in mammospheres and promote reattachment

Cancer stem-like cells (CSC) and circulating tumor cells (CTC) have related properties associated with distant metastasis, but the mechanisms through which CSCs promote metastasis are unclear. In this study, we report that breast cancer cell lines with more stem-like properties display higher levels of microtentacles (McTN), a type of tubulin-based protrusion of the plasma cell membrane that forms on detached or suspended cells and aid in cell reattachment. We hypothesized that CSCs with large numbers of McTNs would more efficiently attach to distant tissues, promoting metastatic efficiency. The naturally occurring stem-like subpopulation of the human mammary epithelial (HMLE) cell line presents increased McTNs compared with its isogenic non-stem-like subpopulation. This increase was supported by elevated α-tubulin detyrosination and vimentin protein levels and organization. Increased McTNs in stem-like HMLEs promoted a faster initial reattachment of suspended cells that was inhibited by the tubulin-directed drug, colchicine, confirming a functional role for McTNs in stem cell reattachment. Moreover, live-cell confocal microscopy showed that McTNs persist in breast stem cell mammospheres as flexible, motile protrusions on the surface of the mammosphere. Although exposed to the environment, they also function as extensions between adjacent cells along cell-cell junctions. We found that treatment with the breast CSC-targeting compound curcumin rapidly extinguished McTN in breast CSC, preventing reattachment from suspension. Together, our results support a model in which breast CSCs with cytoskeletal alterations that promote McTNs can mediate attachment and metastasis but might be targeted by curcumin as an antimetastatic strategy.

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

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

Molecular characterization of circulating tumor cells and individualized cancer diagnosis and therapy

The heterogeneity of cancer cells involved in oncogenesis and metastasis has always been the key factor that impedes tumor diagnosis and treatment (especially traditional chemotherapies). In recent years, molecular characterization of tumors and accordingly implementation of individualized treatment targeting specific molecular markers have become a hotspot for cancer research. As a link between the primary tumor and metastases, circulating tumor cells (CTCs) provide a window into tumor biology and the metastatic cascade. With their real-time, non-invasive and repeatable access, CTCs are excellent resources of tumor specimens. Molecular characterization of CTCs is of great significance for tumor molecular analysis and individualized treatment. Here we review the recent progress in molecular characterization of CTCs and individualized cancer diagnosis and therapy.

Plasticity of disseminating cancer cells in patients with epithelial malignancies

Current models suggest that at a certain but yet undefined time point of tumour development malignant cells with an aggressive phenotype start to disseminate via the blood stream into distant organs. This invasive phenotype appears to be associated with an epithelial-mesenchymal transition (EMT), which enables detachment of tumour cells from a primary site and migration. The reverse process of mesenchymal-epithelial transition (MET) might play a crucial role in the further steps of metastasis when circulating tumour cells (CTCs) settle down in distant organs and establish (micro-)metastasis. Nevertheless, the exact mechanisms and interplay of EMT and MET are only partially understood and their relevance in cancer patients is unclear. Research groups have just started to apply EMT-related markers in their studies on CTCs in cancer patients. In the present review, we summarize and discuss the current state of investigations on CTCs in the context of research on EMT/MET.

Enrichment, detection and clinical significance of circulating tumor cells

Circulating Tumor Cells (CTCs) are shed from primary or secondary tumors into blood circulation. Accessing and analyzing these cells provides a non-invasive alternative to tissue biopsy. CTCs are estimated to be as few as 1 cell among a few million WBCs and few billion RBCs in 1 ml of patient blood and are rarely found in healthy individuals. CTCs are FDA approved for prognosis of the major cancers, namely, Breast, Colon and Prostate. Currently, more than 400 clinical trials are ongoing to establish their clinical significance beyond prognosis, such as, therapy selection and companion diagnostics. Understanding the clinical relevance of CTCs typically involves isolation, detection and molecular characterization of cells, ideally at single cell level. The need for highly reliable, standardized and robust methodologies for isolating and analyzing CTCs has been widely expressed by clinical thought leaders. In the last decade, numerous academic and commercial technology platforms for isolation and analysis of CTCs have been reported. A recent market report highlighted the presence of more than 100 companies offering products and services related to CTCs. This review aims to capture the state of the art and examines the technical merits and limitations of contemporary technologies for clinical use.

Detection of tumor cell-specific mRNA in the peripheral blood of patients with breast cancer—evaluation of several markers with real-time reverse transcription-PCR

It is widely known that cells from epithelial tumors, e.g., breast cancer, detach from their primary tissue and enter blood circulation. We show that the presence of circulating tumor cells (CTCs) in samples of patients with primary and metastatic breast cancer can be detected with an array of selected tumor-marker-genes by reverse transcription real-time PCR. The focus of the presented work is on detecting differences in gene expression between healthy individuals and adjuvant and metastatic breast cancer patients, not an accurate quantification of these differences. Therefore, total RNA was isolated from blood samples of healthy donors and patients with primary or metastatic breast cancer after enrichment of mononuclear cells by density gradient centrifugation. After reverse transcription real-time PCR was carried out with a set of marker genes (BCSP, CK8, Her2, MGL, CK18, CK19). B2M and GAPDH were used as reference genes. Blood samples from patients with metastatic disease revealed increased cytokine gene levels in comparison to normal blood samples. Detection of a single gene was not sufficient to detect CTCs by reverse transcription real-time PCR. Markers used here were selected based on a recent study detecting cancer cells on different protein levels. The combination of such a marker array leads to higher and more specific discovery rates, predominantly in metastatic patients. Identification of CTCs by PCR methods may lead to better diagnosis and prognosis and could help to choose an adequate therapy.

2-NBDG fluorescence imaging of hypermetabolic circulating tumor cells in mouse xenograft model of breast cancer

OBJECTIVES

To determine use of 2-[N-(7-nitrobenz-2-oxa-1,3-diazol-4-yl)amino]-2-deoxy-D-glucose (2-NBDG) as a tracer for detection of hypermetabolic circulating tumor cells (CTC) by fluorescence imaging.

PROCEDURES

Human breast cancer cells were implanted in the mammary gland fat pad of athymic mice to establish orthotopic human breast cancer xenografts as a mouse model of circulating breast cancer cells. Near-infrared fluorescence imaging of the tumor-bearing mice injected with 2-DeoxyGlucosone 750 (2-DG 750) was conducted to assess glucose metabolism of xenograft tumors. Following incubation with fluorescent 2-NBDG, circulating breast cancer cells in the blood samples collected from the tumor-bearing mice were collected by magnetic separation, followed by fluorescence imaging for 2-NBDG uptake by circulating breast cancer cells, and correlation of the number of hypermetabolic circulating breast cancer cells with tumor size at the time when the blood samples were collected.

RESULTS

Human breast cancer xenograft tumors derived from MDA-MB-231, BT474, or SKBR-3 cells were visualized on near-infrared fluorescence imaging of the tumor-bearing mice injected with 2-DG 750. Hypermetabolic circulating breast cancer cells with increased uptake of fluorescent 2-NBDG were detected in the blood samples from tumor-bearing mice and visualized by fluorescence imaging, but not in the blood samples from normal control mice. The number of hypermetabolic circulating breast cancer cells increased along with growth of xenograft tumors, with the number of hypermetabolic circulating breast cancer cells detected in the mice bearing MDA-MB231 xenografts larger than those in the mice bearing BT474 or SKBR-3 xenograft tumors.

CONCLUSIONS

Circulating breast cancer cells with increased uptake of fluorescent 2-NBDG were detected in mice bearing human breast cancer xenograft tumors by fluorescence imaging, suggesting clinical use of 2-NBDG as a tracer for fluorescence imaging of hypermetabolic circulating breast cancer cells.

Circulating tumor cells: from bench to bedside

Circulating tumor cells (CTCs) represent a surrogate biomarker of hematogenous metastases. In recent years, their detection has gained increasing interest. There is ample evidence regarding the ability to detect CTCs and their prognostic relevance, but their demonstrated predictive value in therapeutic response monitoring is clinically even more meaningful. Many clinical trials in the early and metastatic cancer setting now include CTCs as a monitoring parameter, and numerous translational studies attempting their molecular characterization are under way. There has been great progress in defining the clinical importance of CTCs, and it now seems likely that we may expect wider implementation of CTCs as a diagnostic oncology tool to monitor therapeutic response in real time. Novel technologies may further facilitate molecular characterization of CTCs and development of novel therapeutic targets, possibly leading to more powerful treatment strategies for cancer patients. As the detection and evaluation of CTCs are becoming an increasingly important diagnostic and prognostic tool, the goal of this review is to communicate the knowledge obtained through analysis of primary tumors and CTCs to oncologists and medical specialists in managing patients with cancer.