High speed detection of circulating tumor cells

Detection and isolation of circulating tumor cells: principles and methods

Efforts to improve the clinical management of several cancers include finding better methods for the quantitative and qualitative analysis of circulating tumor cells (CTCs). However, detection and isolation of CTCs from the blood circulation is not a trivial task given their scarcity and the lack of reliable markers to identify these cells. With a variety of emerging technologies, a thorough review of the exploited principles and techniques as well as the trends observed in the development of these technologies can assist researchers to recognize the potential improvements and alternative approaches. To help better understand the related biological concepts, a simplified framework explaining cancer formation and its spread to other organs as well as how CTCs contribute to this process has been presented first. Then, based on their basic working-principles, the existing methods for detection and isolation of CTCs have been classified and reviewed as nucleic acid-based, physical properties-based and antibody-based methods. The review of literature suggests that antibody-based methods, particularly in conjunction with a microfluidic lab-on-a-chip setting, offer the highest overall performance for detection and isolation of CTCs. Further biological and engineering-related research is required to improve the existing methods. These include finding more specific markers for CTCs as well as enhancing the throughput, sensitivity, and analytic functionality of current devices.

Isolation and in vitro culture of rare cancer stem cells from patient-derived xenografts of pancreatic ductal adenocarcinoma

Described is the construction of a large array of releasable microstructures (micropallets) along with screening and isolation protocols for sorting rare, approximately 1 in 10,000, cancer stem cells (CSCs) from a heterogeneous cell population. A 10.1 × 7.1 cm array of micropallets (50 × 50 × 75 μm structures and 25 μm micropallet gap) was fabricated on a large glass substrate, providing an array of approximately 1.3 million releasable microstructures. Image analysis algorithms were developed to permit array screening for identification of fluorescently labeled cells in less than 15 min using an epifluorescent wide-field microscope with a computer controlled translational stage. Device operation was tested by culturing HeLa cells transfected with green fluorescent protein (GFP) admixed with wild-type HeLa cells at ratios of 1:10(4) to 1:10(6) on the array followed by screening to identify flourescent cells. Micropallets containing cells of interest were then selectively released by a focused laser pulse and collected on a numbered poly(dimethylsiloxane) (PDMS) substrate with high viability. A direct comparison of this technology with fluorescence-activated cell sorting (FACS) demonstrated that micropallet arrays offered enhanced post sorting purity (100%), yield (100%), and viability (94-100%) for rare cell isolation. As a demonstration of the technology's value, pancreatic tumor cells from Panc-1 cell lines and patient-derived xenografts were screened for the presence of CD24, CD44, and CD326: surface markers of pancreatic CSCs. Following cell isolation and culture, 63 ± 23% of the isolated Panc-1 cells and 35% of sorted human xenograft cells formed tumor spheroids retaining high expression levels of CD24, CD44, and CD326. The ability to isolate rare cells from relatively small sample sizes will facilitate our understanding of cell biology and the development of new therapeutic strategies.

Circulating Tumor Cells Count and Morphological Features in Breast, Colorectal and Prostate Cancer

Background

Presence of circulating tumor cells (CTC) in patients with metastatic breast, colorectal and prostate cancer is indicative for poor prognosis. An automated CTC (aCTC) algorithm developed previously to eliminate the variability in manual counting of CTC (mCTC) was used to extract morphological features. Here we validated the aCTC algorithm on CTC images from prostate, breast and colorectal cancer patients and investigated the role of quantitative morphological parameters.

Methodology

Stored images of samples from patients with prostate, breast and colorectal cancer, healthy controls, benign breast and colorectal tumors were obtained using the CellSearch system. Images were analyzed for the presence of aCTC and their morphological parameters measured and correlated with survival.

Results

Overall survival hazard ratio was not significantly different for aCTC and mCTC. The number of CTC correlated strongest with survival, whereas CTC size, roundness and apoptosis features reached significance in univariate analysis, but not in multivariate analysis. One aCTC/7.5 ml of blood was found in 7 of 204 healthy controls and 9 of 694 benign tumors. In one patient with benign tumor 2 and another 9 aCTC were detected.

Significance of the study

CTC can be identified and morphological features extracted by an algorithm on images stored by the CellSearch system and strongly correlate with clinical outcome in metastatic breast, colorectal and prostate cancer.

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.

Filtration parameters influencing circulating tumor cell enrichment from whole blood

Filtration can achieve circulating tumor cell (CTC) enrichment from blood. Key parameters such as flow-rate, applied pressure, and fixation, vary largely between assays and their influence is not well understood. Here, we used a filtration system, to monitor these parameters and determine their relationships. Whole blood, or its components, with and without spiked tumor cells were filtered through track-etched filters. We characterize cells passing through filter pores by their apparent viscosity; the viscosity of a fluid that would pass with the same flow. We measured a ratio of 5·10(4)∶10(2)∶1 for the apparent viscosities of 15 µm diameter MDA-231 cells, 10 µm white cells and 90 fl red cells passing through a 5 µm pore. Fixation increases the pressure needed to pass cells through 8 µm pores 25-fold and halves the recovery of spiked tumor cells. Filtration should be performed on unfixed samples at a pressure of ∼10 mbar for a 1 cm(2) track-etched filter with 5 µm pores. At this pressure MDA-231 cells move through the filter in 1 hour. If fixation is needed for sample preservation, a gentle fixative should be selected. The difference in apparent viscosity between CTC and blood cells is key in optimizing recovery of CTC.

Filter characteristics influencing circulating tumor cell enrichment from whole blood

A variety of filters assays have been described to enrich circulating tumor cells (CTC) based on differences in physical characteristics of blood cells and CTC. In this study we evaluate different filter types to derive the properties of the ideal filter for CTC enrichment. Between 0.1 and 10 mL of whole blood spiked with cells from tumor cell lines were passed through silicon nitride microsieves, polymer track-etched filters and metal TEM grids with various pore sizes. The recovery and size of 9 different culture cell lines was determined and compared to the size of EpCAM+CK+CD45−DNA+ CTC from patients with metastatic breast, colorectal and prostate cancer. The 8 µm track-etched filter and the 5 µm microsieve had the best performance on MDA-231, PC3-9 and SKBR-3 cells, enriching >80% of cells from whole blood. TEM grids had poor recovery of ∼25%. Median diameter of cell lines ranged from 10.9–19.0 µm, compared to 13.1, 10.7, and 11.0 µm for breast, prostate and colorectal CTC, respectively. The 11.4 µm COLO-320 cell line had the lowest recovery of 17%. The ideal filter for CTC enrichment is constructed of a stiff, flat material, is inert to blood cells, has at least 100,000 regularly spaced 5 µm pores for 1 ml of blood with a ≤10% porosity. While cell size is an important factor in determining recovery, other factors must be involved as well. To evaluate a filtration procedure, cell lines with a median size of 11–13 µm should be used to challenge the system.

Detecting circulating tumor cells: current challenges and new trends

Circulating tumor cells (CTCs) in the blood stream play a critical role in establishing metastases. The clinical value of CTCs as a biomarker for early cancer detection, diagnosis, prognosis, prediction, stratification, and pharmacodynamics have been widely explored in recent years. However, the clinical utility of current CTC tests is limited mainly due to methodological constraints. In this review, the pros and cons of the reported CTC assays are comprehensively discussed. In addition, the potential of tumor cell-derived materials as new targets for CTC detection, including circulating tumor microemboli, cell fragments, and circulating DNA, is evaluated. Finally, emerging approaches for CTC detection, including telomerase-based or aptamer-based assays and cell functional analysis, are also assessed. Expectantly, a thorough review of the current knowledge and technology of CTC detection will assist the scientific community in the development of more efficient CTC assay systems.

An automated high-throughput counting method for screening circulating tumor cells in peripheral blood

Enumeration of circulating tumor cells (CTCs) has proved valuable for early detection and prognosis in cancer treatment. This paper describes an automated high-throughput counting method for CTCs based on microfluidics and line-confocal microscopy. Peripheral blood was directly labeled with multiple antibodies, each conjugated with a different fluorophore, pneumatically pumped through a microfluidic channel, and interrogated by a line-confocal microscope. On the basis of the fluorescence signals and labeling schemes, the count of CTCs was automatically reported. Due to the high flow rate, 1 mL of whole blood can be analyzed in less than 30 min. We applied this method in analyzing CTCs from 90 stage IV breast cancer patient samples and performed a side-by-side comparison with the results of the CellSearch assay, which is the only method approved by the U.S. Food and Drug Administration at present for enumeration of CTCs. This method has a recovery rate for cultured breast cancer cells of 94% (n = 9), with an average of 1.2 counts/mL of background level of detected CTCs from healthy donors. It detected CTCs from breast cancer patients ranging from 15 to 3375 counts/7.5 mL. Using this method, we also demonstrate the ability to enumerate CTCs from breast cancer patients that were positive for Her2 or CD44(+)/CD24(-), which is a putative cancer stem cell marker. This automated method can enumerate CTCs from peripheral blood with high throughput and sensitivity. It could potentially benefit the clinical diagnosis and prognosis of cancer.

Markers of circulating breast cancer cells

The detection of circulating tumor cells (CTC) aids in diagnosis of disease, prognosis, disease recurrence, and therapeutic response. The molecular aspects of metastasis are reviewed including its relevance in the identification and characterization of putative markers that may be useful in the detection thereof. Also discussed are methods for CTC enrichment using molecular strategies. The clinical application of CTC in the metastatic disease process is also summarized.

Time-gated orthogonal scanning automated microscopy (OSAM) for high-speed cell detection and analysis

We report a new development of orthogonal scanning automated microscopy (OSAM) incorporating time-gated detection to locate rare-event organisms regardless of autofluorescent background. The necessity of using long-lifetime (hundreds of microseconds) luminescent biolabels for time-gated detection implies long integration (dwell) time, resulting in slow scan speed. However, here we achieve high scan speed using a new 2-step orthogonal scanning strategy to realise on-the-fly time-gated detection and precise location of 1-μm lanthanide-doped microspheres with signal-to-background ratio of 8.9. This enables analysis of a 15 mm × 15 mm slide area in only 3.3 minutes. We demonstrate that detection of only a few hundred photoelectrons within 100 μs is sufficient to distinguish a target event in a prototype system using ultraviolet LED excitation. Cytometric analysis of lanthanide labelled Giardia cysts achieved a signal-to-background ratio of two orders of magnitude. Results suggest that time-gated OSAM represents a new opportunity for high-throughput background-free biosensing applications.

Microfluidic transport in microdevices for rare cell capture

The isolation and capture of rare cells is a problem uniquely suited to microfluidic devices, in which geometries on the cellular length scale can be engineered and a wide range of chemical functionalizations can be implemented. The performance of such devices is primarily affected by the chemical interaction between the cell and the capture surface and the mechanics of cell-surface collision and adhesion. As rare cell-capture technology has been summarized elsewhere (E. D. Pratt et al., Chem. Eng. Sci. 2011, 66, 1508-1522), this article focuses on the fundamental adhesion and transport mechanisms in rare cell-capture microdevices, and explores modern device design strategies in a transport context. The biorheology and engineering parameters of cell adhesion are defined; adhesion models and reaction kinetics briefly reviewed. Transport at the microscale, including diffusion and steric interactions that result in cell motion across streamlines, is discussed. The review concludes by discussing design strategies with a focus on leveraging the underlying transport phenomena to maximize device performance.

Circulating tumor cells in hepatocellular carcinoma: detection techniques, clinical implications, and future perspectives

Hepatocellular carcinoma (HCC) is a primary liver cancer with a huge challenge in terms of its complex etiology and its management. The fact that the most common site of early tumor recurrence in liver transplantation for HCC is the transplanted allograft strongly suggests that circulating tumor cells (CTCs) are really an active source of HCC metastasis or recurrence. In the past decade, with the tremendous progress in the technology of CTC detection, there is convincing evidence that CTCs have great potential as a marker for metastatic disease and poor prognosis in patients with a malignancy. Currently some interesting and encouraging results have been achieved in HCC CTC detection, although the knowledge about its clinical relevance in HCC is lagging behind other major tumor types. Here we will review existing and developing methodologies for CTC detection, discuss future perspectives, and describe the potential clinical impact of the identification and molecular characterization of CTC subset or circulating cancer stem cells in HCC patients. Particular attention is given to the results based on the HCC CTC study.

Challenges in the enumeration and phenotyping of CTC

PURPOSE

Presence of circulating tumor cells (CTC) in metastatic carcinoma is associated with poor survival. Phenotyping and genotyping of CTC may permit "real-time" treatment decisions, provided CTCs are available for examination. Here, we investigate what is needed to detect CTC in all patients.

EXPERIMENTAL DESIGN

CTCs enumerated in 7.5 mL of blood together with survival from 836 patients with metastatic breast, colorectal, and prostate cancer were used to predict the CTC concentration in the 42% of these patients in whom no CTCs were found and to establish the relation of concentration of CTCs with survival. Influence of different CTC definitions were investigated by automated cell recognition and a flow cytometric assay without an enrichment or permeabilization step.

RESULTS

A log-logistic regression of the log of CTC yielded a good fit to the CTC frequency distribution. Extrapolation of the blood volume to 5 L predicted that 99% of patients had at least one CTC before therapy initiation. Survival of patients with EpCAM+, cytokeratin+, CD45- nucleated CTCs is reduced by 6.6 months for each 10-fold CTC increase. Using flow cytometry, the potential three-fold recovery improvement is not sufficient to detect CTC in all patients in 7.5 mL of blood.

CONCLUSIONS

EpCAM+, cytokeratin+, CD45- nucleated CTCs are present in all patients with metastatic breast, prostate, and colorectal cancer and their frequency is proportional to survival. To serve as a liquid biopsy for the majority of patients, a substantial improvement of CTC yield is needed, which can only be achieved by a dramatic increase in sample volume.

Investigating dynamical deformations of tumor cells in circulation: predictions from a theoretical model

It is inevitable for tumor cells to deal with various mechanical forces in order to move from primary to metastatic sites. In particular, the circulating tumor cells that have detached from the primary tumor and entered into the bloodstream need to survive in a completely new microenvironment. They must withstand hemodynamic forces and overcome the effects of fluid shear before they can leave the vascular system (extravasate) to establish new metastatic foci. One of the hypotheses of the tumor cell extravasation process is based on the so called “adhesion cascade” that was formulated and observed in the context of leukocytes circulating in the vascular system. During this process, the cell needs to switch between various locomotion strategies, from floating with the blood stream, to rolling on the endothelial wall, to tumor cell arrest and crawling, and finally tumor cell transmigration through the endothelial layer. The goal of this project is to use computational mechanical modeling to investigate the fundamental biophysical parameters of tumor cells in circulation. As a first step to build a robust in silico model, we consider a single cell exposed to the blood flow. We examine parameters related to structure of the actin network, cell nucleus and adhesion links between the tumor and endothelial cells that allow for successful transition between different transport modes of the adhesion cascade.

Do circulating tumor cells play a role in coagulation and thrombosis?

Cancer induces a hypercoagulable state, and patients with cancer who suffer a thrombotic event have a worse prognosis than those who do not. Recurrent pathologic thrombi in patients with cancer are clinically managed with anticoagulant medications; however, anticoagulant prophylaxis is not routinely prescribed owing to a complex variety of patient and diagnosis related factors. Early identification of patients at risk for cancer-associated thrombosis would allow for personalization of anticoagulant prophylaxis and likely reduce morbidity and mortality for many cancers. The environment in which a thrombosis develops in a patient with cancer is complex and unique from patients without cancer, which creates therapeutic challenges but may also provide targets for the development of clinical assays in this context. Circulating tumor cells (CTCs) may play a role in the association between cancer and thrombosis. Cancer metastasis, the leading cause of cancer-related deaths, is facilitated by the hematogenous spread of CTCs, and CTCs accompany metastatic disease across all major types of carcinomas. The role of CTCs in the pathogenesis of thrombosis has not been studied due to the previous difficulty in identifying these rare cells, but the interaction between these circulating cells and the coagulation system is an area of study that demands attention. The development of CTC detection platforms presents a new tool by which to characterize the role for CTCs in cancer-related hypercoagulability. In addition, this area of study presents a new avenue for assessing the risk of cancer-associated thrombosis and represents a potential tool for predicting which patients may benefit from anticoagulant prophylaxis. In this review, we will discuss the evidence in support of CTC induced hypercoagulability, and highlight areas where CTC-detection platforms may provide prognostic insight into the risk of developing thrombosis for patients with cancer.

Quantification of cellular volume and sub-cellular density fluctuations: comparison of normal peripheral blood cells and circulating tumor cells identified in a breast cancer patient

Cancer metastasis, the leading cause of cancer-related deaths, is facilitated in part by the hematogenous transport of circulating tumor cells (CTCs) through the vasculature. Clinical studies have demonstrated that CTCs circulate in the blood of patients with metastatic disease across the major types of carcinomas, and that the number of CTCs in peripheral blood is correlated with overall survival in metastatic breast, colorectal, and prostate cancer. While the potential to monitor metastasis through CTC enumeration exists, the basic physical features of CTCs remain ill defined and moreover, the corresponding clinical utility of these physical parameters is unknown. To elucidate the basic physical features of CTCs we present a label-free imaging technique utilizing differential interference contrast (DIC) microscopy to measure cell volume and to quantify sub-cellular mass-density variations as well as the size of subcellular constituents from mass-density spatial correlations. DIC measurements were carried out on CTCs identified in a breast cancer patient using the high-definition (HD) CTC detection assay. We compared the biophysical features of HD-CTC to normal blood cell subpopulations including leukocytes, platelets (PLT), and red blood cells (RBCs). HD-CTCs were found to possess larger volumes, decreased mass-density fluctuations, and shorter-range spatial density correlations in comparison to leukocytes. Our results suggest that HD-CTCs exhibit biophysical signatures that might be used to potentially aid in their detection and to monitor responses to treatment in a label-free fashion. The biophysical parameters reported here can be incorporated into computational models of CTC-vascular interactions and in vitro flow models to better understand metastasis.

Fast multi-spectral imaging technique for detection of circulating endothelial cells in human blood samples

The appearance of non-blood cells circulating in human peripheral bloodstream indicates an abnormal condition. One important category of these cells is circulating endothelial cells (CECs) shed by compromised blood vessels. Clinical applications that measure the blood level of CECs are hindered due to a lack of standardized instruments. The major challenge in detecting circulating non-blood cells is their extreme scarcity; 1 in 106 to 107. Described here is a new method for detection of rare cells in blood samples deposited on the adhesive microscopic slides and immunostained with distinct fluorescent markers. The key novelty of the proposed approach is an intelligent search principle and a dual-mode scanner to implement this principle. To begin, a fast scanning that uses a single beam is performed in the spectral channel where only rare cells produce florescence. Once a target cell is registered, the scanner switches on the imaging mode, auto-focuses and then records images in multiple spectral channels at the selected area. The instrument runs in repetitive cycles until the entire slide is scanned. The technology has been validated via detection of human umbilical vein endothelial cells spiked into human blood samples. In addition, the operational principle can be adapted for detection of other types of rare cells in blood.

Circulating tumor cells in the diagnosis and management of pancreatic cancer

Pancreatic cancers are typically resistant to chemo and radiation therapy and are predisposed to distant metastases. Circulating tumor cells (CTCs) are tumor cells disseminated from primary and metastatic sites and can be isolated from peripheral blood. CTC may overcome the limitation of the current available tumor markers, CA19-9. As a surrogate for 'real-time biopsy', CTCs allow recurrent assessment of a tumor's biological activity. We review the current methodologies for CTC extraction and characterization including antibody-based immunological assays, PCR-based assays, and novel technologies based on the physical or biological characteristics of CTCs. CTCs also provide an accessible link to the existence of epithelial to mesenchymal transition, tumor stem cell markers, and ongoing clonal mutations and epigenetic changes in the tumor. We also explore the potential of using CTC profiling in diagnosis, selection of neoadjuvant and adjuvant therapy, detection of recurrent disease, examination of pharmacodynamic biomarkers, as well as in gene therapy and immunotherapy for pancreatic cancer. Ongoing CTC characterization not only has the potential to represent all cells shed from primary pancreatic tumor and each metastatic site, but also allows dynamic sampling at multiple time points during the clinical course to identify the subpopulations of CTCs and the specific molecules driving metastasis and chemo resistance. We predict that CTC genotyping and phenotyping will play an increasing role in personalized therapy and in identification of novel therapeutic targets as well as monitoring the course and status of the disease.

Sensitive and high-throughput isolation of rare cells from peripheral blood with ensemble-decision aliquot ranking

This paper describes an approach called ensemble decision aliquot ranking (eDAR) for isolating rare cells from peripheral blood. eDAR has a recovery of over 93% (n=9) with a zero false positive rate (n=8) , and provides direct easy access to individual isolated live cells for downstream single-cell manipulation and analysis. We anticipate eDAR will enable new studies of various types of rare cells that circulate in blood.

ERCC1 expression in circulating tumor cells (CTCs) using a novel detection platform correlates with progression-free survival (PFS) in patients with metastatic non-small-cell lung cancer (NSCLC) receiving platinum chemotherapy

PURPOSE

To utilize a novel circulating tumor cell (CTC) technology to quantify ERCC1 expression on CTCs and determine whether ERCC1 expression levels predict efficacy of platinum-based chemotherapy in patients with metastatic non-small-cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

ERCC1 expression was measured in 17 metastatic NSCLC patients who received platinum-based therapy and had ≥2 intact CTCs with acceptable ERCC1 expression assay results. ERCC1 levels were determined from average expression on individual CTCs in each sample. Progression-free survival (PFS) was calculated from the date of therapy initiation.

RESULTS

PFS decreased with increasing ERCC1 expression (p<0.04, F-test, linear regression). Lack of ERCC1 expression was associated with longer PFS (266 days versus 172 days, log-rank, p<0.02) in a Kaplan-Meier analysis using ERCC expression level of 1 as a cutoff (range 0-30). The difference in survival was statistically significant with a hazard ratio of 4.20 (95% CI 1.25-14.1, p<0.02, log-rank). PFS was also observed to decrease with increased cytokeratin (CK) expression (p<0.01 long-rank (Cox regression) and F-test (linear regression)). The hazard ratio is 4.38 (95% CI 1.76-10.9) for each log-change in CK value until progression was noted on imaging.

CONCLUSION

Low expression of ERCC1 on CTCs correlates with PFS in patients with metastatic NSCLC receiving platinum-based therapy.

Molecular biology techniques for the surgeon

New technologies are constantly being introduced into the medical and surgical fields. These technologies come in the form of newer medicines, imaging methods and prognostic tools, among others, and allow clinicians to make more rational and informed decisions on the care of their patients. Many of these technologies utilize advanced techniques which are at the forefront of many research fields and represent a transition of bench advances into the clinical realm. This review will highlight four technologies that are at the forefront in the treatment of oncology patients treated by surgeons on a daily basis. Circulating tumor cells, microarray analysis, proteomic studies and rapid sequencing technologies will be highlighted. These technologies will be reviewed and their potential use in the care of surgical patients will be discussed.

A stochastic Markov chain model to describe lung cancer growth and metastasis

A stochastic Markov chain model for metastatic progression is developed for primary lung cancer based on a network construction of metastatic sites with dynamics modeled as an ensemble of random walkers on the network. We calculate a transition matrix, with entries (transition probabilities) interpreted as random variables, and use it to construct a circular bi-directional network of primary and metastatic locations based on postmortem tissue analysis of 3827 autopsies on untreated patients documenting all primary tumor locations and metastatic sites from this population. The resulting 50 potential metastatic sites are connected by directed edges with distributed weightings, where the site connections and weightings are obtained by calculating the entries of an ensemble of transition matrices so that the steady-state distribution obtained from the long-time limit of the Markov chain dynamical system corresponds to the ensemble metastatic distribution obtained from the autopsy data set. We condition our search for a transition matrix on an initial distribution of metastatic tumors obtained from the data set. Through an iterative numerical search procedure, we adjust the entries of a sequence of approximations until a transition matrix with the correct steady-state is found (up to a numerical threshold). Since this constrained linear optimization problem is underdetermined, we characterize the statistical variance of the ensemble of transition matrices calculated using the means and variances of their singular value distributions as a diagnostic tool. We interpret the ensemble averaged transition probabilities as (approximately) normally distributed random variables. The model allows us to simulate and quantify disease progression pathways and timescales of progression from the lung position to other sites and we highlight several key findings based on the model.

Fluid biopsy in patients with metastatic prostate, pancreatic and breast cancers

Hematologic spread of carcinoma results in incurable metastasis; yet, the basic characteristics and travel mechanisms of cancer cells in the bloodstream are unknown. We have established a fluid phase biopsy approach that identifies circulating tumor cells (CTCs) without using surface protein-based enrichment and presents them in sufficiently high definition (HD) to satisfy diagnostic pathology image quality requirements. This 'HD-CTC' assay finds >5 HD-CTCs mL(-1) of blood in 80% of patients with metastatic prostate cancer (n = 20), in 70% of patients with metastatic breast cancer (n = 30), in 50% of patients with metastatic pancreatic cancer (n = 18), and in 0% of normal controls (n = 15). Additionally, it finds HD-CTC clusters ranging from 2 HD-CTCs to greater than 30 HD-CTCs in the majority of these cancer patients. This initial validation of an enrichment-free assay demonstrates our ability to identify significant numbers of HD-CTCs in a majority of patients with prostate, breast and pancreatic cancers.

Emerging technologies for CTC detection based on depletion of normal cells

Properly conducted, an enrichment step can improve selectivity, sensitivity, yield, and most importantly, significantly reduce the time needed to isolate rare circulating tumor cells (CTCs). The enrichment process can be broadly categorized as positive selection versus negative depletion, or in some cases, a combination of both. We have developed a negative depletion CTC enrichment strategy that relies on the removal of normal cells using immunomagnetic separation in the blood of cancer patients. This method is based on the combination of magnetic and fluid forces in an axial, laminar flow in long cylinders placed in quadrupole magnets. Using this technology, we have successfully isolated CTCs from patients with breast carcinoma and squamous cell carcinoma of the head and neck. In contrast to a positive selection methodology, this approach provides an unbiased characterization of these cells, including markers associated with epithelial mesenchymal transition.

Advances in optical technologies for rare cell detection and characterization

Scanning cytometry enables detection of circulating tumor cells without enrichment, minimizing potential loss of sensitivity due to variable expression of enrichment targets; however, some approaches lack specificity without imaging to identify false positives. High fidelity imaging enables identification of CTCs using morphological considerations and semi-quantitative measurement of biomarker expression for predicting targeted therapy but often lacks speed needed for the large number of mononuclear blood cells. A hybrid approach of first scanning a sample at high speed and high numerical aperture to locate CTCs followed by high resolution imaging of a small number of objects reduces the time needed for high resolution imaging without loss of detection sensitivity.

Circulating tumor cells measurements in hepatocellular carcinoma

Liver cancer is the fifth most common cancer in men and the seventh in women. During the past 20 years, the incidence of HCC has tripled while the 5-year survival rate has remained below 12%. The presence of circulating tumor cells (CTC) reflects the aggressiveness nature of a tumor. Many attempts have been made to develop assays that reliably detect and enumerate the CTC during the development of the HCC. In this case, the challenges are (1) there are few markers specific to the HCC (tumor cells versus nontumor cells) and (2) they can be used to quantify the number of CTC in the bloodstream. Another technical challenge consists of finding few CTC mixed with million leukocytes and billion erythrocytes. CTC detection and identification can be used to estimate prognosis and may serve as an early marker to assess antitumor activity of treatment. CTC can also be used to predict progression-free survival and overall survival. CTC are an interesting source of biological information in order to understand dissemination, drug resistance, and treatment-induced cell death. Our aim is to review and analyze the different new methods existing to detect, enumerate, and characterize the CTC in the peripheral circulation of patients with HCC.

Nanoparticle induced cell magneto-rotation: monitoring morphology, stress and drug sensitivity of a suspended single cancer cell

Single cell analysis has allowed critical discoveries in drug testing, immunobiology and stem cell research. In addition, a change from two to three dimensional growth conditions radically affects cell behavior. This already resulted in new observations on gene expression and communication networks and in better predictions of cell responses to their environment. However, it is still difficult to study the size and shape of single cells that are freely suspended, where morphological changes are highly significant. Described here is a new method for quantitative real time monitoring of cell size and morphology, on single live suspended cancer cells, unconfined in three dimensions. The precision is comparable to that of the best optical microscopes, but, in contrast, there is no need for confining the cell to the imaging plane. The here first introduced cell magnetorotation (CM) method is made possible by nanoparticle induced cell magnetization. By using a rotating magnetic field, the magnetically labeled cell is actively rotated, and the rotational period is measured in real-time. A change in morphology induces a change in the rotational period of the suspended cell (e.g. when the cell gets bigger it rotates slower). The ability to monitor, in real time, cell swelling or death, at the single cell level, is demonstrated. This method could thus be used for multiplexed real time single cell morphology analysis, with implications for drug testing, drug discovery, genomics and three-dimensional culturing.

The Role of Cancer Stem Cells in the Organ Tropism of Breast Cancer Metastasis: A Mechanistic Balance between the "Seed" and the "Soil"?

Breast cancer is a prevalent disease worldwide, and the majority of deaths occur due to metastatic disease. Clinical studies have identified a specific pattern for the metastatic spread of breast cancer, termed organ tropism; where preferential secondary sites include lymph node, bone, brain, lung, and liver. A rare subpopulation of tumor cells, the cancer stem cells (CSCs), has been hypothesized to be responsible for metastatic disease and therapy resistance. Current treatments are highly ineffective against metastatic breast cancer, likely due to the innate therapy resistance of CSCs and the complex interactions that occur between cancer cells and their metastatic microenvironments. A better understanding of these interactions is essential for the development of novel therapeutic targets for metastatic disease. This paper summarizes the characteristics of breast CSCs and their potential metastatic microenvironments. Furthermore, it raises the question of the existence of a CSC niche and highlights areas for future investigation.

Circulating tumor cells as biomarkers in prostate cancer

Unmet needs in prostate cancer drug development and patient management are the ability to monitor treatment effects and to identify therapeutic targets in a tumor at the time treatment is being considered. This review focuses on establishing analytically valid biomarkers for specific contexts of use in patients with castration-resistant prostate cancer (CRPC), emphasizing a biomarker currently in clinical use, circulating tumor cells (CTC). The FDA Critical Path provides a road map for these investigations, which, if followed, will facilitate the incorporation of these types of assays into clinical decision-making. CTC enumeration at baseline and post-treatment is prognostic of survival, with no threshold effect, and the shedding of cells into the circulation represents an intrinsic property of the tumor, distinct from extent of disease. The clinical utility of monitoring CTC changes with treatment, as an efficacy-response surrogate biomarker of survival, is currently being tested in large phase III trials, with the novel antiandrogen therapies abiraterone acetate and MDV3100. Molecular determinants can be identified and characterized in CTCs as potential predictive biomarkers of tumor sensitivity to a therapeutic modality. Additionally, we discuss novel technologies to enrich and characterize CTCs from more patients, the potential clinical uses of CTCs in determining prognosis and monitoring treatment effects, and CTCs as a source of tissue to identify predictive markers of drug sensitivity to guide treatment selection. Prospective studies, designed around the biomarker itself and the specific clinical context for which it is applied, are needed to further assess the role of these and novel markers in clinical practice.

A new method for high speed, sensitive detection of minimal residual disease

Investigations of rare cell types in peripheral blood samples, such as tumor, fetal, and endothelial cells, represent an emerging field with several potentially valuable medical applications. Peripheral blood is a particularly attractive body fluid for the detection of rare cells as its collection is minimally invasive and can be repeated throughout the course of the disease. Because the number of rare cells in mononuclear cells can be very low (1 in 10 million), a large number of cells must be quickly screened, which places demanding requirements on the screening technology. While enrichment technology has shown promise in managing metastatic disease, enrichment can cause distortions of cell morphology that limit pathological identification, and the enrichment targeting adds additional constraints that can affect sensitivity. Here, we describe a new approach for detecting rare leukemia cells that does not require prior enrichment. We have developed an immunocytochemical assay for identification of leukemia cells spiked in peripheral blood samples, and a high-speed scanning instrument with high numerical aperture and wide field of view to efficiently locate these cells in large sample sizes. A multiplex immunoassay with four biomarkers was used to uniquely identify the rare cells from leukocytes and labeling artifacts. The cytometer preserves the cell morphology and accurately locates labeled rare cells for subsequent high resolution imaging. The sensitivity and specificity of the approach show promise for detection of a low number of leukemia cells in blood (1 in 10 million nucleated cells). The method enables rapid location of rare circulating cells (25 M cells/min), no specific enrichment step, and excellent imaging of cellular morphology with multiple immunofluorescent markers. The cell imaging is comparable to other imaging approaches such as laser scan cytometry and image flow cytometry, but the cell analysis rate is many orders of magnitude faster making this approach practical for detection of rare cells.

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 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.

Multiple biomarker expression on circulating tumor cells in comparison to tumor tissues from primary and metastatic sites in patients with locally advanced/inflammatory, and stage IV breast cancer, using a novel detection technology

Patients with locally advanced/inflammatory breast cancer (LABC/IBC) face a high likelyhood of recurrence and prognosis for relapsed, or de novo stage IV metastatic breast cancer (MBC) remains poor. Estrogen (ER) and HER2 receptor expression on primary or MBC allow targeted therapies, but an estimated 10-18% of tumors do not exhibit these biomarkers and survival in these cases is even poorer. Variations in discordance rates for the expression of ER and HER2 receptors have been observed between primary and metastatic tumors and such discordances may lead to suboptimal treatment. Circulating tumor cells (CTCs) are considered the seeds of residual disease and distant metastases and their characterization could help guide treatment selection. To explore this possibility, we used multiple biomarker assessment of CTCs in comparison to primary and metastatic tumor sites. Thirty-six patients with LABC/IBC, or stage IV MBC were evaluated. Blood samples were procured prior to initiating or changing therapy. CTCs were identified based on presence of cytokeratin and nucleus staining, and the absence of CD45. A multimarker assay was developed to simultaneously quantify expression of HER2, ER, and ERCC1, a DNA excision repair protein. Novel fiber-optic array scanning technology (FAST) was used for sensitive location of CTCs. CTCs were detected in 82% of MBC and 62% LABC/IBC cases. Multiplex marker expression was successfully carried out in samples from18 patients with MBC and in 8 patients with LABC/IBC that contained CTCs. In MBC, we detected actionable discordance rates of 40 and 23%, respectively for ER and HER2 where a biomarker was negative in the primary or metastatic tumor and positive in the CTCs. In LABC/IBC, actionable discordances were 60 and 20% for ER and HER2, respectively. Pilot trials evaluating the effectiveness of treatment selections based on actionable discordances between biomarker expression patterns on CTCs and primary or metastatic tumor sites may allow for a prospective assessment of CTC-based individualized targeted therapies.

Automated genotyping of circulating tumor cells

Cancer remains a prominent health concern in modern societies. Continuous innovations and introduction of new technologies are essential to level or reduce current healthcare spending. A diagnostic platform to detect circulating tumor cells (CTCs) in peripheral blood may be most promising in this respect. CTCs have been proposed as a minimally invasive, prognostic and predictive marker to reflect the biological characteristics of tumors and are implemented in an increasing number of clinical studies. Still, their detection remains a challenge as they may occur at concentrations below one single cell per ml of blood. To facilitate their detection, here we describe microfluidic modules to isolate and genotype CTCs directly from clinical blood samples. In a first cell isolation and detection module, the CTCs are immunomagnetically enriched, separated and counted. In a second module and after cell lysis, the mRNA is reversely transcripted to cDNA, followed by a multiplex ligation probe amplification of 20 specific genetic markers and two control fragments. Following the multiplex ligation probe amplification reaction, the amplified fragments are electrochemically detected in a third and final module. Besides the design of the modules, their functionality is described using control samples. Further testing using clinical samples and integration of all modules in a single, fully automated smart miniaturized system will enable minimal invasive testing for frequent detection and characterization of CTCs.

Sequential array cytometry: multi-parameter imaging with a single fluorescent channel

Heterogeneity within the human population and within diseased tissues necessitates a personalized medicine approach to diagnostics and the treatment of diseases. Functional assays at the single-cell level can contribute to uncovering heterogeneity and ultimately assist in improved treatment decisions based on the presence of outlier cells. We aim to develop a platform for high-throughput, single-cell-based assays using well-characterized hydrodynamic cell isolation arrays which allow for precise cell and fluid handling. Here, we demonstrate the ability to extract spatial and temporal information about several intracellular components using a single fluorescent channel, eliminating the problem of overlapping fluorescence emission spectra. Integrated with imaging technologies such as wide field-of-view lens-free fluorescent imaging, fiber-optic array scanning technology, and microlens arrays, use of a single fluorescent channel will reduce the cost of reagents and optical components. Specifically, we sequentially stain hydrodynamically trapped cells with three biochemical labels all sharing the same fluorescence excitation and emission spectrum. These markers allow us to analyze the amount of DNA, and compare nucleus-to-cytoplasm ratio, as well as glycosylation of surface proteins. By imaging cells in real-time we enable measurements of temporal localization of cellular components and intracellular reaction kinetics, the latter is used as a measurement of multi-drug resistance. Demonstrating the efficacy of this single-cell analysis platform is the first step in designing and implementing more complete assays, aimed toward improving diagnosis and personalized treatments to complex diseases.

Advancing personalized cancer therapy by detection and characterization of circulating carcinoma cells

Early dissemination, blood circulation, or homing of single tumor cells in bone marrow and other organs is usually undetectable at primary diagnosis, even by high resolution imaging technologies. However, ultrasensitive approaches now enable the detection of "occult" tumor cells. Many researchers are currently focusing on circulating tumor cells (CTC) in peripheral blood, and several publications have described associations of CTC in patients with metastatic cancer and worse prognosis. However, evidence has emerged that the currently used detection methods lack sensitivity or specificity to track all CTC, especially those that have lost characteristic epithelial features. Therefore, new developments in this field are of utmost interest and will be reviewed here. Moreover, molecular CTC analysis will provide insights into the selection of tumor cells and resistance mechanisms in patients undergoing systemic therapies. This information might support assessing individual prognosis, stratifying patients at risk to systemic therapies, and monitoring therapeutic efficacy.

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.

All circulating EpCAM+CK+CD45- objects predict overall survival in castration-resistant prostate cancer

BACKGROUND

Presence of five or more circulating tumor cells (CTC) in patients with metastatic carcinomas is associated with poor survival. Although many objects positive for epithelial cell adhesion molecules and cytokeratin (EpCAM+CK+) are not counted as CTC, they may be an important predictor for survival. We evaluated the association between these objects and survival in patients with prostate cancer.

PATIENTS AND METHODS

Included in this follow-up study were 179 patients with castration-resistant prostate cancer. CellSearch was used to isolate EpCAM+ objects and to stain DNA, cytokeratin and CD45. All EpCAM+CK+ objects were subdivided into seven classes on the basis of predefined morphological appearance in 63 independent samples. Association of each class with survival was studied using Kaplan-Meier and Cox regression analyses.

RESULTS

Each EpCAM+CK+CD45- class showed a strong association with overall survival (P < 0.001). This included small tumor microparticles (S-TMP), which did not require a nucleus and thus are unable to metastasize. A higher number of objects in any class was associated with decreased survival. A good prediction model included large tumor cell fragments (L-TCF), age, hemoglobin and lactate dehydrogenase. Models with S-TMP or CTC instead of L-TCF performed similarly.

CONCLUSION

EpCAM+CK+CD45- that do not meet strict definitions for CTC are strong prognostic markers for survival.

Detection of melanoma cells in vitro using an optical detector of photoacoustic waves

BACKGROUND AND OBJECTIVE

Circulating tumor cells have been shown to correlate positively with metastatic disease state in patients with advanced cancer. We have demonstrated the ability to detect melanoma cells in a flow system by generating and detecting photoacoustic waves in melanoma cells. This method is similar to flow cytometry, although using photoacoustics rather than fluorescence. Previously, we used piezoelectric films as our acoustic sensors. However, such films have indicated false-positive signals due to unwanted direct interactions between photons from the high laser fluence in the flow system and the film itself. We have adapted an optical detection scheme that obviates the need for piezoelectric films.

STUDY DESIGN/MATERIALS AND METHODS

Our photoacoustic system comprised a tunable laser system with an output of 410-710 nm with a pulse duration of 5 nanoseconds. The light was delivered by optical fiber to a glass microcuvette that contained saline buffer suspensions of melanoma and white blood cells. We used a continuous HeNe laser to provide a probe beam that reflected off of a glass and water interface in close proximity to the microcuvette. The beam was detected by a high-speed photodiode. When a photoacoustic wave was generated in the microcuvette, the wave propagated and changed the reflectance of the beam due to index of refraction change in the water. This perturbation was used to detect the presence of melanoma cells.

RESULTS

We determined a detection threshold of about one individual melanoma cell with no pyroelectric noise indicated in the signals.

CONCLUSIONS

The optical reflectance method provides sensitivity to detect small numbers of melanoma cells without created false-positive signals from pyroelectric interference, showing promise as a means to perform tests for circulating melanoma cells in blood samples.