Characterization of circulating tumor cells by fluorescence in situ hybridization

Biomarkers and computational models for predicting efficacy to tumor ICI immunotherapy

Numerous studies have shown that immune checkpoint inhibitor (ICI) immunotherapy has great potential as a cancer treatment, leading to significant clinical improvements in numerous cases. However, it benefits a minority of patients, underscoring the importance of discovering reliable biomarkers that can be used to screen for potential beneficiaries and ultimately reduce the risk of overtreatment. Our comprehensive review focuses on the latest advancements in predictive biomarkers for ICI therapy, particularly emphasizing those that enhance the efficacy of programmed cell death protein 1 (PD-1)/programmed cell death-ligand 1 (PD-L1) inhibitors and cytotoxic T-lymphocyte antigen-4 (CTLA-4) inhibitors immunotherapies. We explore biomarkers derived from various sources, including tumor cells, the tumor immune microenvironment (TIME), body fluids, gut microbes, and metabolites. Among them, tumor cells-derived biomarkers include tumor mutational burden (TMB) biomarker, tumor neoantigen burden (TNB) biomarker, microsatellite instability (MSI) biomarker, PD-L1 expression biomarker, mutated gene biomarkers in pathways, and epigenetic biomarkers. TIME-derived biomarkers include immune landscape of TIME biomarkers, inhibitory checkpoints biomarkers, and immune repertoire biomarkers. We also discuss various techniques used to detect and assess these biomarkers, detailing their respective datasets, strengths, weaknesses, and evaluative metrics. Furthermore, we present a comprehensive review of computer models for predicting the response to ICI therapy. The computer models include knowledge-based mechanistic models and data-based machine learning (ML) models. Among the knowledge-based mechanistic models are pharmacokinetic/pharmacodynamic (PK/PD) models, partial differential equation (PDE) models, signal networks-based models, quantitative systems pharmacology (QSP) models, and agent-based models (ABMs). ML models include linear regression models, logistic regression models, support vector machine (SVM)/random forest/extra trees/k-nearest neighbors (KNN) models, artificial neural network (ANN) and deep learning models. Additionally, there are hybrid models of systems biology and ML. We summarized the details of these models, outlining the datasets they utilize, their evaluation methods/metrics, and their respective strengths and limitations. By summarizing the major advances in the research on predictive biomarkers and computer models for the therapeutic effect and clinical utility of tumor ICI, we aim to assist researchers in choosing appropriate biomarkers or computer models for research exploration and help clinicians conduct precision medicine by selecting the best biomarkers.

Complementary Tumor Diagnosis by Single Cell-Based Cytogenetics Using Multi-marker Fluorescence In Situ Hybridization (mFISH)

Multi-color (or multi-marker) fluorescence in situ hybridization (mFISH) is a well-established, valuable, complementary tool for prenatal and pathological (tumor) diagnosis. A variety of chromosomal abnormalities, such as partial or total chromosomal gains, losses, inversions, or translocations, which are considered to cause genetic syndromes, can relatively easily be detected on a cell-by-cell basis. Individual cells either in suspension (e.g., in the form of a cytological specimen derived from body fluids) or within a tissue (e.g., a solid tumor specimen or biopsy) can be quantitatively evaluated with respect to the chromosomal hybridization markers of interest (e.g., a gene or centromeric region) and with due consideration of cellular heterogeneity. FISH is helpful or even essential for the (sub-)classification, stratification, and unambiguous diagnosis of a number of malignant diseases and contributes to treatment decision in many cases. Here, the diagnostic power and limitations of typical FISH and mFISH approaches (except chromosome painting and RNA hybridization) are discussed, with special emphasis on tumor and single-cell diagnostics. Well-established and novel FISH protocols, the latter addressed to accelerate and flexibilize the preparation and hybridization of formalin-fixed and paraffin-embedded tissues, are provided. Moreover, guidelines and molecular aspects important for data interpretation are discussed. Finally, sophisticated multiplexed approaches and those that analyze very rare single-cell events, which are not yet implemented in diagnostic procedures, will be touched upon. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol 1: (m)FISH applied to formaldehyde-fixed paraffin-embedded tissues Basic Protocol 2: (m)FISH applied to cytological specimens.

Unraveling Cancer Metastatic Cascade Using Microfluidics-based Technologies

Cancer has long been a leading cause of death. The primary tumor, however, is not the main cause of death in more than 90% of cases. It is the complex process of metastasis that makes cancer deadly. The invasion metastasis cascade is the multi-step biological process of cancer cell dissemination to distant organ sites and adaptation to the new microenvironment site. Unraveling the metastasis process can provide great insight into cancer death prevention or even treatment. Microfluidics is a promising platform, that provides a wide range of applications in metastasis-related investigations. Cell culture microfluidic technologies for in vitro modeling of cancer tissues with fluid flow and the presence of mechanical factors have led to the organ-on-a-chip platforms. Moreover, microfluidic systems have also been exploited for capturing and characterization of circulating tumor cells (CTCs) that provide crucial information on the metastatic behavior of a tumor. We present a comprehensive review of the recent developments in the application of microfluidics-based systems for analysis and understanding of the metastasis cascade from a wider perspective.

Clinical significance of circulating tumour cells and tumour marker detection in the chemotherapeutic evaluation of advanced colorectal cancer

AIM

Systemic chemotherapy combining biological targeted therapies is the standard therapy for patients with metastatic colorectal cancer (mCRC), but effective markers are needed to identify clinical responders. Circulating tumour cells (CTCs) have been associated with prognosis in patients with mCRC. This study aimed to explore the relationship between CTC number and the clinical response of patients with advanced CRC.

METHOD

Epithelial cell adhesion molecule-independent enrichment and CD45^- fluorescence in situ hybridization immunofluorescence were used to detect peripheral blood CTCs in 79 patients with advanced CRC. Fisher's exact test and Spearman's rank correlation coefficient were used to analyse the correlation between CTC number and efficacy of chemotherapy. Kaplan-Meier and Cox regression analyses were used to evaluate progression-free survival (PFS).

RESULTS

Among the evaluable patients, CTCs were significantly correlated with clinical response (r =4.891, p = 0.031). High CTC numbers were associated with a poor treatment response (r = -0.250, p = 0.027). Dynamic decrease in CTC number was associated with clinical response (p = 0.046). High baseline CTC number and carcinoembryonic antigen levels were prognostic factors for unfavourable PFS in multivariable analysis [hazard ratio (HR) = 3.30, p = 0.011 and HR = 2.04, p = 0.044, respectively]. Compared with the CTC-positive group, the CTC-negative group showed superior PFS (median PFS 15.53 vs. 9.43 months, p = 0.041) among CRC patients receiving first-line treatment.

CONCLUSION

CTC number is a feasible biomarker for predicting outcomes in mCRC patients receiving systemic chemotherapy.

Circulating Tumor Cells: A Promising Biomarker in the Management of Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is a malignancy that arises from the mucosal epithelium of the nasopharynx, and its prognosis is relatively favorable. The 5-year overall survival rate in patients with locally advanced NPC currently exceeds 80%, but the development of individualized diagnosis and treatment at the molecular level is relatively lacking. Circulating tumor cells (CTCs) is the generic term for tumor cells that are present in the peripheral blood circulation. As a new biomarker with good clinical application prospects, the detection of CTCs has the advantages of being non-invasive, simple, and repeatable. By capturing and detecting CTCs in peripheral blood and monitoring the dynamic variation of its type and quantity, we can assess the biological characteristics of tumor in a timely manner and evaluate the therapeutic effect and prognosis of patients in advance, which will help to develop individualized treatments of tumors. The primary purposes of this review were the clinical application of CTCs in tumor stage determination, treatment efficacy evaluation, and prognosis prediction of NPC. In addition, we estimated the correlation between Epstein-Barr virus infection and CTCs and analyzed the difference in karyotypes and specific markers expressed on CTCs. We believe that our study will provide new insights and biomarkers for the individualized treatment of patients with NPC.

Circulating tumor cell profiling for precision oncology

Analysis of circulating tumor cells (CTCs) collected from patient's blood offers a broad range of opportunities in the field of precision oncology. With new advances in profiling technology, it is now possible to demonstrate an association between the molecular profiles of CTCs and tumor response to therapy. In this Review, we discuss mechanisms of tumor resistance to therapy and their link to phenotypic and genotypic properties of CTCs. We summarize key technologies used to isolate and analyze CTCs and discuss recent clinical studies that examined CTCs for genomic and proteomic predictors of responsiveness to therapy. We also point out current limitations that still hamper the implementation of CTCs into clinical practice. We finally reflect on how these shortcomings can be addressed with the likely contribution of multiparametric approaches and advanced data analytics.

Tumor Evolution and Therapeutic Choice Seen through a Prism of Circulating Tumor Cell Genomic Instability

Circulating tumor cells (CTCs) provide an accessible tool for investigating tumor heterogeneity and cell populations with metastatic potential. Although an in-depth molecular investigation is limited by the extremely low CTC count in circulation, significant progress has been made recently in single-cell analytical processes. Indeed, CTC monitoring through molecular and functional characterization may provide an understanding of genomic instability (GI) molecular mechanisms, which contribute to tumor evolution and emergence of resistant clones. In this review, we discuss the sources and consequences of GI seen through single-cell analysis of CTCs in different types of tumors. We present a detailed overview of chromosomal instability (CIN) in CTCs assessed by fluorescence in situ hybridization (FISH), and we reveal utility of CTC single-cell sequencing in identifying copy number alterations (CNA) oncogenic drivers. We highlight the role of CIN in CTC-driven metastatic progression and acquired resistance, and we comment on the technical obstacles and challenges encountered during single CTC analysis. We focus on the DNA damage response and depict DNA-repair-related dynamic biomarkers reported to date in CTCs and their role in predicting response to genotoxic treatment. In summary, the suggested relationship between genomic aberrations in CTCs and prognosis strongly supports the potential utility of GI monitoring in CTCs in clinical risk assessment and therapeutic choice.

HER2 expression on tumor-derived extracellular vesicles and circulating tumor cells in metastatic breast cancer

Background

Tumor-derived extracellular vesicles (tdEVs) and circulating tumor cells (CTCs) in the blood of metastatic cancer patients associate with poor outcomes. In this study, we explored the human epidermal growth factor receptor 2 (HER2) expression on CTCs and tdEVs of metastatic breast cancer patients.

Methods

Blood samples from 98 patients (CLCC-IC-2006-04 study) were originally processed with the CellSearch® system using the CTC kit and anti-HER2 as an additional marker in the staining cocktail. CTCs and tdEVs were automatically enumerated from the generated CellSearch images using the open-source ACCEPT software.

Results

CTCs and tdEVs were subdivided based on their cytokeratin (CK) and HER2 phenotype into CK+HER2−, CK−HER2+, and CK+HER2+. The inclusion of anti-HER2 increased the percentage of informative samples with ≥ 1 detectable CTC from 89 to 95%. CK− CTCs and tdEVs correlated equally well with the clinical outcome as CK+ CTCs and tdEVs. Inter- and intra-patient heterogeneity was found for the CTC/tdEV phenotypes, and the presence of 2 or 3 classes of CTCs/tdEVs was associated with worse prognosis compared to a uniform CTC/tdEV phenotype present (1 class). The use of ≥ 7% HER2+CK+ tdEVs can predict HER2 expression of the tissue with 74% sensitivity and specificity using the HER2 amplification status of the primary tumor as a classification variable.

Conclusions

HER2 can be detected on CTCs and tdEVs not expressing CK, and these CK− CTCs/tdEVs have similar clinical relevance to CTCs and tdEVs expressing CK. tdEVs perform better than CTCs in predicting the HER2 status of the primary tissue. CTC and tdEV heterogeneity in the blood of patients is inversely associated with overall survival.

Evolution of Estrogen Receptor Status from Primary Tumors to Metastasis and Serially Collected Circulating Tumor Cells

Background: The estrogen receptor (ER) can change expression between primary tumor (PT) and distant metastasis (DM) in breast cancer. A tissue biopsy reflects a momentary state at one location, whereas circulating tumor cells (CTCs) reflect real-time tumor progression. We evaluated ER-status during tumor progression from PT to DM and CTCs, and related the ER-status of CTCs to prognosis. Methods: In a study of metastatic breast cancer, blood was collected at different timepoints. After CellSearch^® enrichment, CTCs were captured on DropMount slides and evaluated for ER expression at baseline (BL) and after 1 and 3 months of therapy. Comparison of the ER-status of PT, DM, and CTCs at different timepoints was performed using the McNemar test. The primary endpoint was progression-free survival (PFS). Results: Evidence of a shift from ER positivity to negativity between PT and DM was demonstrated (p = 0.019). We found strong evidence of similar shifts from PT to CTCs at different timepoints (p < 0.0001). ER-positive CTCs at 1 and 3 months were related to better prognosis. Conclusions: A shift in ER-status from PT to DM/CTCs was demonstrated. ER-positive CTCs during systemic therapy might reflect the retention of a favorable phenotype that still responds to therapy.

Liquid Biopsy as Novel Tool in Precision Medicine: Origins, Properties, Identification and Clinical Perspective of Cancer's Biomarkers

In recent years, there has been an increase in knowledge of cancer, accompanied by a technological development that gives rise to medical oncology. An instrument that allows the implementation of individualized therapeutic strategies is the liquid biopsy. Currently, it is the most innovative methodology in medical oncology. Its high potential as a tool for screening and early detection, the possibility of assessing the patient’s condition after diagnosis and relapse, as well as the effectiveness of real-time treatments in different types of cancer. Liquid biopsy is capable of overcoming the limitations of tissue biopsies. The elements that compose the liquid biopsy are circulating tumor cells, circulating tumor nucleic acids, free of cells or contained in exosomes, microvesicle and platelets. Liquid biopsy studies are performed on various biofluids extracted in a non-invasive way, and they can be performed both from the blood and in urine, saliva or cerebrospinal fluid. The development of genotyping techniques, using the elements that make up liquid biopsy, make it possible to detect mutations, intertumoral and intratumoral heterogeneity, and provide molecular information on cancer for application in medical oncology in an individualized way in different types of tumors. Therefore, liquid biopsy has the potential to change the way medical oncology could predict the course of the disease.

Post-enrichment circulating tumor cell detection and enumeration via deformability impedance cytometry

Circulating tumor cells (CTCs) in blood can provide valuable information when detecting, diagnosing, and monitoring cancer. This paper describes a system that consists of a constriction-based microfluidic sensor with embedded electrodes that can detect and enumerate cancer cells in blood. The biosensor measures impedance in terms of magnitude and phase at multiple frequencies as cells transit through the constriction channel. Cancer cells deform as they move through while blood cells remain intact, thus generating differential impedance profiles that can be used for detecting and counting CTCs. Two versions of this device are reported, one where the electrodes are embedded into the disposable microfluidic channel, and the other in which the disposable chip is externally fixed to a reusable substrate housing the electrodes. Both configurations were tested by spiking breast or prostate cancer cells into murine blood, and both detected all tumor cells passing through the narrow channels while being able to differentiate between the two cell lines. The chip in its current format has a throughput of 1 μL/min. While the throughput is scalable by integrating more constriction channels in parallel, the presented assay is intended for post-enrichment label-free enumeration and characterization of CTCs.

Genetic Analysis of Circulating Tumour Cells

The classification of human cancers has traditionally relied on the tissue of origin, the histologic appearance and anatomical extent of disease, otherwise referred to as grade and stage. However, this system fails to explain the highly variable clinical behaviour seen for any one cancer. Molecular characterization through techniques such as next-generation sequencing (NGS) has led to an appreciation of the extreme genetic heterogeneity that underlies most human cancers. Because of the difficulties associated with fresh tissue biopsy, interest has increased in using circulating tumour material, such as circulating tumour cells (CTCs), as a non-invasive way to access tumour tissue. CTC enumeration has been demonstrated to have prognostic value in metastatic breast, colon and prostate cancers. Recent studies have also shown that CTCs are suitable material for molecular characterization, using techniques such as reverse transcription-polymerase chain reaction (RT-PCR), fluorescence in situ hybridization (FISH), array comparative genomic hybridization (aCGH) and NGS. Furthermore, genetic analysis of CTCs may be more suitable to study tumour heterogeneity and clonal evolution than fresh tissue biopsy. Whether blood-based biopsy techniques will be accepted as a replacement to fresh tissue biopsies remains to be seen, but there is reason for optimism. While significant barriers to this acceptance exist, blood-based biopsy techniques appear to be reliable and representative alternatives to fresh tissue biopsy.

Analysis of Released Circulating Tumor Cells During Surgery for Non-Small Cell Lung Cancer

PURPOSE

Tumor cells from patients with lung cancer are expelled from the primary tumor into the blood, but difficult to detect in the peripheral circulation. We studied the release of circulating tumor cells (CTCs) during surgery to test the hypothesis that CTC counts are influenced by hemodynamic changes (caused by surgical approach) and manipulation.

EXPERIMENTAL DESIGN

Patients undergoing video-assisted thoracic surgery (VATS) or open surgery for (suspected) primary lung cancer were included. Blood samples were taken before surgery (T0) from the radial artery (RA), from both the RA and pulmonary vein (PV) when the PV was located (T1) and when either the pulmonary artery (T2 open) or the PV (T2 VATS) was dissected. The CTCs were enumerated using the CellSearch system. Single-cell whole-genome sequencing was performed on isolated CTCs for aneuploidy.

RESULTS

CTCs were detected in 58 of 138 samples (42%) of 31 patients. CTCs were more often detected in the PV (70%) compared with the RA (22%, P < 0.01) and in higher counts (P < 0.01). After surgery, the RA but not the PV showed less often CTCs (P = 0.02). Type of surgery did not influence CTC release. Only six of 496 isolated CTCs showed aneuploidy, despite matched primary tumor tissue being aneuploid. Euploid so-called CTCs had a different morphology than aneuploid.

CONCLUSIONS

CTCs defined by CellSearch were identified more often and in higher numbers in the PV compared with the RA, suggesting central clearance. The majority of cells in the PV were normal epithelial cells and outnumbered CTCs. Release of CTCs was not influenced by surgical approach.

Liquid biopsy in pancreatic ductal adenocarcinoma: current status of circulating tumor cells and circulating tumor DNA

Reliable biomarkers are required to evaluate and manage pancreatic ductal adenocarcinoma. Circulating tumor cells and circulating tumor DNA are shed into blood and can be relatively easily obtained from minimally invasive liquid biopsies for serial assays and characterization, thereby providing a unique potential for early diagnosis, forecasting disease prognosis, and monitoring of therapeutic response. In this review, we provide an overview of current technologies used to detect circulating tumor cells and circulating tumor DNA and describe recent advances regarding the multiple clinical applications of liquid biopsy in pancreatic ductal adenocarcinoma.

Hydro-Seq enables contamination-free high-throughput single-cell RNA-sequencing for circulating tumor cells

Molecular analysis of circulating tumor cells (CTCs) at single-cell resolution offers great promise for cancer diagnostics and therapeutics from simple liquid biopsy. Recent development of massively parallel single-cell RNA-sequencing (scRNA-seq) provides a powerful method to resolve the cellular heterogeneity from gene expression and pathway regulation analysis. However, the scarcity of CTCs and the massive contamination of blood cells limit the utility of currently available technologies. Here, we present Hydro-Seq, a scalable hydrodynamic scRNA-seq barcoding technique, for high-throughput CTC analysis. High cell-capture efficiency and contamination removal capability of Hydro-Seq enables successful scRNA-seq of 666 CTCs from 21 breast cancer patient samples at high throughput. We identify breast cancer drug targets for hormone and targeted therapies and tracked individual cells that express markers of cancer stem cells (CSCs) as well as of epithelial/mesenchymal cell state transitions. Transcriptome analysis of these cells provides insights into monitoring target therapeutics and processes underlying tumor metastasis.

Molecular Profiling of Liquid Biopsy Samples for Precision Medicine

In the context of oncology, liquid biopsies consist of harvesting cancer biomarkers, such as circulating tumor cells, tumor-derived cell-free DNA, and extracellular vesicles, from bodily fluids. These biomarkers provide a source of clinically actionable molecular information that can enable precision medicine. Herein, we review technologies for the molecular profiling of liquid biopsy markers with special emphasis on the analysis of low abundant markers from mixed populations.

Scanning Electron Microscopy of Circulating Tumor Cells and Tumor-Derived Extracellular Vesicles

To explore morphological features of circulating tumor cells (CTCs) and tumor-derived extracellular vesicles (tdEVs), we developed a protocol for scanning electron microscopy (SEM) of CTCs and tdEVs. CTCs and tdEVs were isolated by immunomagnetic enrichment based on their Epithelial Cell Adhesion Molecule (EpCAM) expression or by physical separation through 5 μm microsieves from 7.5 mL of blood from Castration-Resistant Prostate Cancer (CRPC) patients. Protocols were optimized using blood samples of healthy donors spiked with PC3 and LNCaP cell lines. CTCs and tdEVs were identified among the enriched cells by fluorescence microscopy. The positions of DNA+, CK+, CD45- CTCs and DNA-, CK+, CD45- tdEVs on the CellSearch cartridges and microsieves were recorded. After gradual dehydration and chemical drying, the regions of interest were imaged by SEM. CellSearch CTCs retained their morphology revealing various shapes, some of which were clearly associated with CTCs undergoing apoptosis. The ferrofluid was clearly distinguishable, shielding major portions of all isolated objects. CTCs and leukocytes on microsieves were clearly visible, but revealed physical damage attributed to the physical forces that cells exhibit while entering one or multiple pores. tdEVs could not be identified on the microsieves as they passed through the pores. Insights on the underlying mechanism of each isolation technique could be obtained. Complete detailed morphological characteristics of CTCs are, however, masked by both techniques.

How to Agree on a CTC: Evaluating the Consensus in Circulating Tumor Cell Scoring

For using counts of circulating tumor cells (CTCs) in the clinic to aid a physician's decision, its reported values will need to be accurate and comparable between institutions. Many technologies have become available to enumerate and characterize CTCs, thereby showing a large range of reported values. Here we introduce an Open Source CTC scoring tool to enable comparison of different reviewers and facilitate the reach of a consensus on assigning objects as CTCs. One hundred images generated from two different platforms were used to assess concordance between 15 reviewers and an expert panel. Large differences were observed between reviewers in assigning objects as CTCs urging the need for computer recognition of CTCs. A demonstration of a deep learning approach on the 100 images showed the promise of this technique for future CTC enumeration. © 2018 The Authors. Cytometry Part A published by Wiley Periodicals, Inc. on behalf of International Society for Advancement of Cytometry.

Toward a real liquid biopsy in metastatic breast and prostate cancer: Diagnostic LeukApheresis increases CTC yields in a European prospective multicenter study (CTCTrap)

Frequently, the number of circulating tumor cells (CTC) isolated in 7.5 mL of blood is too small to reliably determine tumor heterogeneity and to be representative as a “liquid biopsy”. In the EU FP7 program CTCTrap, we aimed to validate and optimize the recently introduced Diagnostic LeukApheresis (DLA) to screen liters of blood. Here we present the results obtained from 34 metastatic cancer patients subjected to DLA in the participating institutions. About 7.5 mL blood processed with CellSearch® was used as “gold standard” reference. DLAs were obtained from 22 metastatic prostate and 12 metastatic breast cancer patients at four different institutions without any noticeable side effects. DLA samples were prepared and processed with different analysis techniques. Processing DLA using CellSearch resulted in a 0–32 fold increase in CTC yield compared to processing 7.5 mL blood. Filtration of DLA through 5 μm pores microsieves was accompanied by large CTC losses. Leukocyte depletion of 18 mL followed by CellSearch yielded an increase of the number of CTC but a relative decrease in yield (37%) versus CellSearch DLA. In four out of seven patients with 0 CTC detected in 7.5 mL of blood, CTC were detected in DLA (range 1–4 CTC). The CTC obtained through DLA enables molecular characterization of the tumor. CTC enrichment technologies however still need to be improved to isolate all the CTC present in the DLA.

What's new?

Circulating tumor cells (CTC) can mirror tumor heterogeneity but a standard blood sample (7.5 mL) is too small to truly represent the tumor. To increase the yield of CTC, the authors used Diagnostic LeukApheresis in which liters of blood are screened for the presence of CTC in metastatic cancer patients. They report a significant increase in CTC yield and consequently, a better molecular characterization of the tumor, encouraging further research into the use of leukapheresis as “liquid biopsy” in cancer patients.

Engineering cell heterogeneity into organs-on-a-chip

Organ-on-a-chip development is an application that will benefit from advances in cell heterogeneity characterization because these culture models are intended to mimic in vivo microenvironments, which are complex and dynamic. Due in no small part to advances in microfluidic single cell analysis methods, cell-to-cell variability is an increasingly understood feature of physiological tissues, with cell types from as common as 1 out of every 2 cells to as rare as 1 out of every 100 000 cells having important roles in the biochemical and biological makeup of tissues and organs. Variability between neighboring cells can be transient or maintained, and ordered or stochastic. This review covers three areas of well-studied cell heterogeneity that are informative for organ-on-a-chip development efforts: tumors, the lung, and the intestine. Then we look at how recent single cell analysis strategies have enabled better understanding of heterogeneity within in vitro and in vivo tissues. Finally, we provide a few work-arounds for adapting current on-chip culture methods to better mimic physiological cell heterogeneity including accounting for crucial rare cell types and events.

Aneuploid CTC and CEC

Conventional circulating tumor cell (CTC) detection technologies are restricted to large tumor cells (> white blood cells (WBCs)), or those unique carcinoma cells with double positive expression of surface epithelial cell adhesion molecule (EpCAM) for isolation, and intracellular structural protein cytokeratins (CKs) for identification. With respect to detecting the full spectrum of highly heterogeneous circulating rare cells (CRCs), including CTCs and circulating endothelial cells (CECs), it is imperative to develop a strategy systematically coordinating all tri-elements of nucleic acids, biomarker proteins, and cellular morphology, to effectively enrich and comprehensively identify CRCs. Accordingly, a novel strategy integrating subtraction enrichment and immunostaining-fluorescence in situ hybridization (SE-iFISH), independent of cell size variation and free of hypotonic damage as well as anti-EpCAM perturbing, has been demonstrated to enable in situ phenotyping multi-protein expression, karyotyping chromosome aneuploidy, and detecting cytogenetic rearrangements of the ALK gene in non-hematologic CRCs. Symbolic non-synonymous single nucleotide variants (SNVs) of both the TP53 gene (P33R) in each single aneuploid CTCs, and the cyclin-dependent kinase inhibitor 2A (CDKN2A) tumor suppressor gene in each examined aneuploid CECs, were identified for the first time across patients with diverse carcinomas. Comprehensive co-detecting observable aneuploid CTCs and CECs by SE-iFISH, along with applicable genomic and/or proteomic single cell molecular profiling, are anticipated to facilitate elucidating how those disparate categories of aneuploid CTCs and CECs cross-talk and functionally interplay with tumor angiogenesis, therapeutic drug resistance, tumor progression, and cancer metastasis.

Circulating tumor cell isolation, culture, and downstream molecular analysis

Circulating tumor cells (CTCs) are a major contributor of cancer metastases and hold a promising prognostic significance in cancer detection. Performing functional and molecular characterization of CTCs provides an in-depth knowledge about this lethal disease. Researchers are making efforts to design devices and develop assays for enumeration of CTCs with a high capture and detection efficiency from whole blood of cancer patients. The existing and on-going research on CTC isolation methods has revealed cell characteristics which are helpful in cancer monitoring and designing of targeted cancer treatments. In this review paper, a brief summary of existing CTC isolation methods is presented. We also discuss methods of detaching CTC from functionalized surfaces (functional assays/devices) and their further use for ex-vivo culturing that aid in studies regarding molecular properties that encourage metastatic seeding. In the clinical applications section, we discuss a number of cases that CTCs can play a key role for monitoring metastases, drug treatment response, and heterogeneity profiling regarding biomarkers and gene expression studies that bring treatment design further towards personalized medicine.

Liquid Biopsy in Lung Cancer: Clinical Applications of Circulating Biomarkers (CTCs and ctDNA)

Lung cancer is by far the leading cause of cancer death worldwide, with non-small cell lung cancer (NSCLC) accounting for the majority of cases. Recent advances in the understanding of the biology of tumors and in highly sensitive detection technologies for molecular analysis offer targeted therapies, such as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors. However, our understanding of an individual patient’s lung cancer is often limited by tumor accessibility because of the high risk and invasive nature of current tissue biopsy procedures. “Liquid biopsy”, the analysis of circulating biomarkers from peripheral blood, such as circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), offers a new source of cancer-derived materials that may reflect the status of the disease better and thereby contribute to more personalized treatment. In this review, we examined the clinical significance and uniqueness of CTCs and ctDNA from NSCLC patients, isolation and detection methods developed to analyze each type of circulating biomarker, and examples of clinical studies of potential applications for early diagnosis, prognosis, treatment monitoring, and prediction of resistance to therapy. We also discuss challenges that remain to be addressed before such tools are implemented for routine use in clinical settings.

Electrochemical biosensor for cancer cell detection based on a surface 3D micro-array

The detection of rare circulating tumour cells (CTCs) in patients' blood is crucial for the early diagnosis of cancer, highly precise cancer therapy and monitoring therapeutic outcomes in real time. In this study we have developed an efficient strategy to capture and detect CTCs from the blood of cancer patients using a benzoboric acid modified gold-plated polymeric substrate with a regular 3D surface array. Compared with the smooth substrate, the substrate with the surface 3D microarrays exhibited a higher capture efficiency, i.e. 3.8 times that afforded by the smooth substrate. Additionally, due to the reversible reaction between the benzoboric acid on the 3D microarray and the sialic acid on CTCs, our strategy allowed for easy detachment of the captured CTCs from the substrate without causing critical damage to the cells. This will be of benefit for gaining further access to these rare cells for downstream characterization. The proposed strategy provides several advantages, including enhanced capture efficiency, high sensitivity, low cost and recovery of isolated CTCs, and could become a promising platform for early stage diagnosis of cancer.

Functionalization of nanotextured substrates for enhanced identification of metastatic breast cancer cells

Metastasis is the major cause of low survival rates among cancer patients. Once cancer cells metastasize, it is extremely difficult to contain the disease. We report on a nanotextured platform for enhanced detection of metastatic cells. We captured metastatic (MDA-MDB-231) and non-metastatic (MCF-7) breast cancer cells on anti-EGFR aptamer modified plane and nanotextured substrates. Metastatic cells were seen to change their morphology at higher rates when captured on nanotextured substrates than on plane substrates. Analysis showed statistically different morphological behaviors of metastatic cells that were very pronounced on the nanotextured substrates. Several distance matrices were calculated to quantify the dissimilarity of cell shape change. Nanotexturing increased the dissimilarity of the metastatic cells and as a result the contrast between metastatic and non-metastatic cells increased. Jaccard distance measurements found that the shape change ratio of the non-metastatic and metastatic cells was enhanced from 1:1.01 to 1:1.81, going from plane to nanotextured substrates. The shape change ratio of the non-metastatic to metastatic cells improved from 1:1.48 to 1:2.19 for the Hausdorff distance and from 1:1.87 to 1:4.69 for the Mahalanobis distance after introducing nanotexture. Distance matrix analysis showed that nanotexture increased the shape change ratios of non-metastatic and metastatic cells. Hence, the detectability of metastatic cells increased. These calculated matrices provided clear and explicit measures to discriminate single cells for their metastatic state on functional nanotextured substrates.

Comprehensive in situ co-detection of aneuploid circulating endothelial and tumor cells

Conventional circulating tumor cell (CTC) detection strategies rely on cell surface marker EpCAM and intracellular cytokeratins (CKs) for isolation and identification, respectively. Application of such methods is considerably limited by inherent heterogeneous and dynamic expression or absence of EpCAM and/or CKs in CTCs. Here, we report a novel strategy, integrating antigen-independent subtraction enrichment and immunostaining-FISH (SE-iFISH), to detect a variety of aneuploid circulating rare cells (CRCs), including CTCs and circulating tumor endothelial cells (CECs). Enriched CRCs, maintained at high viability and suitable for primary tumor cell culture, are comprehensively characterized by in situ co-examination of chromosome aneuploidy by FISH and immunostaining of multiple biomarkers displayed in diverse fluorescence channels. We described and quantified for the first time the existence of individual aneuploid CD31⁺ CECs and co-existence of "fusion clusters" of endothelial-epithelial aneuploid tumor cells among enriched non-hematopoietic CRCs. Hence, SE-iFISH is feasible for efficient co-detection and in situ phenotypic and karyotypic characterization as well as quantification of various CRCs, allowing for their classification into diverse subtypes upon biomarker expression and chromosome ploidy. Enhanced SE-iFISH technology, assisted by the Metafer-iFISH automated CRC imaging system, provides a platform for the analysis of potential contributions of each subtype of CRCs to distinct clinical outcome.

Analysis of circulating tumor cells from lung cancer patients with multiple biomarkers using high-performance size-based microfluidic chip

Circulating tumor cells (CTCs) have attracted pretty much attention from scientists because of their important relationship with the process of metastasis. Here, we developed a size-based microfluidic chip containing triangular pillar array and filter channel array for detecting single CTCs and CTC clusters independent of tumor-specific markers. The cell populations in chip were characterized by immune-fluorescent staining combining an epithelial marker and a mesenchymal marker. We largely decreased the whole time of detection process to nearly 1.5h with this microfluidic device. The CTCs were subsequently measured in 77 patients with lung cancer and 39 healthy persons. The microfluidic device allowed for the detection of CTCs with apparent high sensitivity and specificity (82.7% sensitivity and 100% specificity). Furthermore, the total CTC counts were found to be elevated in advanced patients with metastases when compared with those without (20.89±14.57 vs 8.428±5.858 cells/mL blood; P<0.01). Combined epithelial marker and mesenchymal marker analysis of CTCs could provide more information about metastasis in patients than only usage of epithelial marker. In conclusion, the development of the size-based microfluidic device for efficient capture of CTCs will enable detailed characterization of their biological properties and values in cancer diagnosis.

Aptamer-functionalized nano/micro-materials for clinical diagnosis: isolation, release and bioanalysis of circulating tumor cells

Detection of rare circulating tumor cells (CTCs) in peripheral blood is a challenging, but necessary, task in order to diagnose early onset of metastatic cancer and to monitor treatment efficacy. Over the last decade, step-up produced aptamers have attracted great attention in clinical diagnosis. They have offered great promise for a broader range of cell-specific recognition and isolation. In particular, aptamer-functionalized magnetic particles for selective extraction of target CTCs have shown reduced damage to cells and relatively simple operation. Also, efforts to develop aptamer-functionalized microchannel/microstructures able to efficiently isolate target CTCs are continuing, and these efforts have brought more advanced geometrically designed substrates. Various aptamer-mediated cell release techniques are being developed to enable subsequent biological studies. This article reviews some of these advances in aptamer-functionalized nano/micro-materials for CTCs isolation and methods for releasing captured CTCs from aptamer-functionalized surfaces. Biological studies of CTCs after release are also discussed.

Improving the CellSearch® system

INTRODUCTION

The CellSearch® CTC test enumerates tumor cells present in 7.5 ml blood of cancer patients. improvements, extensions and different utilities of the cellsearch system are discussed in this paper. Areas covered: This paper describes work performed with the CellSearch system, which go beyond the normal scope of the test. All results from searches with the search term 'CellSearch' from Web of Science and PubMed were categorized and discussed. Expert commentary: The CellSearch Circulating Tumor Cell test captures and identifies tumor cells in blood that are associated with poor clinical outcome. How to best use CTC in clinical practice is being explored in many clinical trials. The ability to extract information from the CTC to guide therapy will expand the potential clinical utility of CTC.

A FISH-based method for assessment of HER-2 amplification status in breast cancer circulating tumor cells following CellSearch isolation

Introduction

Amplification of the HER-2/neu (HER-2) proto-oncogene occurs in 10%–15% of primary breast cancer, leading to an activated HER-2 receptor, augmenting growth of cancer cells. Tumor classification is determined in primary tumor tissue and metastatic biopsies. However, malignant cells tend to alter their phenotype during disease progression. Circulating tumor cell (CTC) analysis may serve as an alternative to repeated biopsies. The Food and Drug Administration-approved CellSearch system allows determination of the HER-2 protein, but not of the HER-2 gene. The aim of this study was to optimize a fluorescence in situ hybridization (FISH)-based method to quantitatively determine HER-2 amplification in breast cancer CTCs following CellSearch-based isolation and verify the method in patient samples.

Methods

Using healthy donor blood spiked with human epidermal growth factor receptor 2 (HER-2)-positive breast cancer cell lines, SKBr-3 and BT-474, and a corresponding negative control (the HER-2-negative MCF-7 cell line), an in vitro CTC model system was designed. Following isolation in the CellSearch system, CTC samples were further enriched and fixed on microscope slides. Immunocytochemical staining with cytokeratin and 4′,6-diamidino-2′-phenylindole dihydrochloride identified CTCs under a fluorescence microscope. A FISH-based procedure was optimized by applying the HER2 IQFISH pharmDx assay for assessment of HER-2 amplification status in breast cancer CTCs.

Results

A method for defining the presence of HER-2 amplification in single breast cancer CTCs after CellSearch isolation was established using cell lines as positive and negative controls. The method was validated in blood from breast cancer patients showing that one out of six patients acquired CTC HER-2 amplification during treatment against metastatic disease.

Conclusion

HER-2 amplification status of CTCs can be determined following CellSearch isolation and further enrichment. FISH is superior to protein assessment of HER-2 status in predicting response to HER-2-targeted immunotherapy in breast cancer patients. This assay has the potential of identifying patients with a shift in HER-2 status who may benefit from treatment adjustments.

Frequent detection of PIK3CA mutations in single circulating tumor cells of patients suffering from HER2-negative metastatic breast cancer

Modern technologies enable detection and characterization of circulating tumor cells (CTC) in peripheral blood samples. Thus, CTC have attracted interest as markers for therapeutic response in breast cancer. First studies have incorporated CTC analyses to guide therapeutic interventions and stratification of breast cancer patients. Aim of this study was to analyze characteristic features of CTC as biomarker for predicting resistance to HER2-targeted therapies. Therefore, CTC from metastatic breast cancer patients with HER2-negative primary tumors screened for the prospective randomized phase III trial DETECT III were explored for their HER2 status and the presence of PIK3CA mutations. Detection and characterization of HER2 expression of CTC were conducted with the CellSearch(®) system. Fifteen of 179 CTC-positive patients (8.4%) contained ≥1 CTC with strong HER2 expression. Genomic DNA from individual CTC isolated by micromanipulation was propagated by whole genome amplification and analyzed for PIK3CA mutations in exons 9 and 20 by Sanger sequencing. One or more CTC/7.5 mL were detected in 179/290 patients (61.7%). In 109 patients (34.8%), ≥5 CTC/7.5 mL were found. We detected at least one CTC with the mutation p.E542K, p.E545K, p.H1047R, p.H1047L or p.M1043V in 12/33 patients (36.4%). Thirty six of 114 CTC (31.6%) harbored one of these mutations. CTC in individual patients exhibited heterogeneity concerning PIK3CA mutations and HER2 expression. In conclusion, clinically relevant genomic aberrations such as mutations in the hotspot regions of exon 9 and 20 of the PIK3CA gene can be detected in single CTC and might provide insights into mechanisms of resistance to HER2-targeted therapies.

Circulating Tumor Cell Isolation and Analysis

Isolation and analysis of cancer cells from body fluids have significant implications in diagnosis and therapeutic treatment of cancers. Circulating tumor cells (CTCs) are cancer cells circulating in the peripheral blood or spreading iatrogenically into blood vessels, which is an early step in the cascade of events leading to cancer metastasis. Therefore, CTCs can be used for diagnosing for therapeutic treatment, prognosing a given anticancer intervention, and estimating the risk of metastatic relapse. However, isolation of CTCs is a significant technological challenge due to their rarity and low recovery rate using traditional purification techniques. Recently microfluidic devices represent a promising platform for isolating cancer cells with high efficiency in processing complex cellular fluids, with simplicity, sensitivity, and throughput. This review summarizes recent methods of CTC isolation and analysis, as well as their applications in clinical studies.

The use of circulating tumor cells in guiding treatment decisions for patients with metastatic castration-resistant prostate cancer

The therapeutic landscape of metastatic castration-resistant prostate cancer (mCRPC) has drastically changed over the past decade with the advent of several new anti-tumor agents. Oncologists increasingly face dilemmas concerning the best treatment sequence for individual patients since most of the novel compounds have been investigated and subsequently positioned either pre- or post-docetaxel. A currently unmet need exists for biomarkers able to guide treatment decisions and to capture treatment resistance at an early stage thereby allowing for an early change to an alternative strategy. Circulating tumor cells (CTCs) have in this context intensively been investigated over the last years. The CTC count, as determined by the CellSearch System (Janssen Diagnostics LLC, Raritan, NJ), is a strong, independent prognostic factor for overall survival in patients with mCRPC at various time points during treatment and, as an early response marker, outperforms traditional response evaluations using serum prostate specific antigen (PSA) levels, scintigraphy as well as radiography. The focus of research is now shifting toward the predictive value of CTCs and the use of the characterization of CTCs to guide the selection of treatments with the highest chance of success for individual patients. Recently, the presence of the androgen receptor splice variant 7 (AR-V7) has been shown to be a promising predictive factor. In this review, we have explored the clinical value of the enumeration and characterization of CTCs for the treatment of mCRPC and have put the results obtained from recent studies investigating the prognostic and predictive value of CTCs into clinical perspective.

Development of a Novel c-MET-Based CTC Detection Platform

Amplification of the MET oncogene is associated with poor prognosis, metastatic dissemination, and drug resistance in many malignancies. We developed a method to capture and characterize circulating tumor cells (CTC) expressing c-MET using a ferromagnetic antibody. Immunofluorescence was used to characterize cells for c-MET, DAPI, and pan-CK, excluding CD45(+) leukocytes. The assay was validated using appropriate cell line controls spiked into peripheral blood collected from healthy volunteers (HV). In addition, peripheral blood was analyzed from patients with metastatic gastric, pancreatic, colorectal, bladder, renal, or prostate cancers. CTCs captured by c-MET were enumerated, and DNA FISH for MET amplification was performed. The approach was highly sensitive (80%) for MET-amplified cells, sensitive (40%-80%) for c-MET-overexpressed cells, and specific (100%) for both c-MET-negative cells and in 20 HVs. Of 52 patients with metastatic carcinomas tested, c-MET CTCs were captured in replicate samples from 3 patients [gastric, colorectal, and renal cell carcinoma (RCC)] with 6% prevalence. CTC FISH demonstrated that MET amplification in both gastric and colorectal cancer patients and trisomy 7 with gain of MET gene copies in the RCC patient. The c-MET CTC assay is a rapid, noninvasive, sensitive, and specific method for detecting MET-amplified tumor cells. CTCs with MET amplification can be detected in patients with gastric, colorectal, and renal cancers.

IMPLICATIONS

This study developed a novel c-MET CTC assay for detecting c-MET CTCs in patients with MET amplification and warrants further investigation to determine its clinical applicability. Mol Cancer Res; 14(6); 539-47. ©2016 AACR.

Challenges in circulating tumor cell detection by the CellSearch system

Enumeration and characterization of circulating tumor cells (CTC) hold the promise of a real time liquid biopsy. They are however present in a large background of hematopoietic cells making their isolation technically challenging. In 2004, the CellSearch system was introduced as the first and only FDA cleared method designed for the enumeration of circulating tumor cells in 7.5 mL of blood. Presence of CTC detected by CellSearch is associated with poor prognosis in metastatic carcinomas. CTC remaining in patients after the first cycles of therapy indicates a futile therapy. Here we review challenges faced during the development of the CellSearch system and the difficulties in assigning objects as CTC. The large heterogeneity of CTC and the different approaches introduced in recent years to isolate, enumerate and characterize CTC results in a large variation of the number of CTC reported urging the need for uniform definitions and at least a clear definition of what the criteria are for assigning an object as a CTC.

Heterogeneity of miR-10b expression in circulating tumor cells

Circulating tumor cells (CTCs) in the blood of cancer patients are recognized as important potential targets for future anticancer therapies. As mediators of metastatic spread, CTCs are also promising to be used as ‘liquid biopsy’ to aid clinical decision-making. Recent work has revealed potentially important genotypic and phenotypic heterogeneity within CTC populations, even within the same patient. MicroRNAs (miRNAs) are key regulators of gene expression and have emerged as potentially important diagnostic markers and targets for anti-cancer therapy. Here, we describe a robust in situ hybridization (ISH) protocol, incorporating the CellSearch^® CTC detection system, enabling clinical investigation of important miRNAs, such as miR-10b on a cell by cell basis. We also use this method to demonstrate heterogeneity of such as miR-10b on a cell-by-cell basis. We also use this method to demonstrate heterogeneity of miR-10b in individual CTCs from breast, prostate and colorectal cancer patients.

Construction of carbon nanotube based nanoarchitectures for selective impedimetric detection of cancer cells in whole blood

A carbon nanotube (CNT) based nanoarchitecture is developed for rapid, sensitive and specific detection of cancer cells by using real time electrical impedance sensing. The sensor is constructed with carbon nanotube (CNT) multilayers and EpCAM (epithelial cell adhesion molecule) antibodies, which are assembled on an indium tin oxide (ITO) electrode surface. The binding of tumor cells to EpCAM antibodies causes increase of the electron-transfer resistance. The electrochemical impedance of the prepared biosensors is linear with the logarithm of concentration of the liver cancer cell line (HepG2) within the concentration range of 10 to 10(5) cells per mL. The detection limit for HepG2 cells is 5 cells per mL. The proposed impedimetric sensing devices allow for sensitive and specific detection of cancer cells in whole-blood samples without any sample pretreatment steps.

Nanotextured polymer substrates show enhanced cancer cell isolation and cell culture

Detection of circulating tumor cells (CTCs) in the early stages of cancer is a great challenge because of their exceedingly small concentration. There are only a few approaches sensitive enough to differentiate tumor cells from the plethora of other cells in a sample like blood. In order to detect CTCs, several antibodies and aptamers have already shown high affinity. Nanotexture can be used to mimic basement membrane to further enhance this affinity. This article reports an approach to fabricate nanotextured polydimethylsiloxane (PDMS) substrates using micro reactive ion etching (micro-RIE). Three recipes were used to prepare nanotextured PDMS using oxygen and carbon tetrafluoride. Micro-RIE provided better control on surface properties. Nanotexturing improved the affinity of PDMS surfaces to capture cancer cells using surface immobilized aptamers against cell membrane overexpressed with epidermal growth factor receptors. In all cases, nanotexture of PDMS increased the effective surface area by creating nanoscale roughness on the surface. Nanotexture also enhanced the growth rate of cultured cells compared to plain surfaces. A comparison among the three nanotextured surfaces demonstrated an almost linear relationship between the surface roughness and density of captured tumor cells. The nanotextured PDMS mimicked biophysical environments for cells to grow faster. This can have many implications in microfluidic platforms used for cell handling.

Clinical significance of phenotyping and karyotyping of circulating tumor cells in patients with advanced gastric cancer

BACKGROUND

Karyotyping and phenotyping of circulating tumor cells (CTCs) in therapeutic cancer patients is of particular clinical significance in terms of both identifying chemo-resistant CTC subtypes and understanding CTC evolution.

METHODS

The integrated subtraction enrichment (SET) and immunostaining-fluorescence in situ hybridization (iFISH) platform was applied to detect and characterize CTCs in patients with advanced gastric cancer (AGC). Status of human epidermal growth factor receptor 2 (HER2) expressing and aneuploidy of chromosome 8 in CTCs enriched from the patients was examined by SET-iFISH following clinical chemotherapy or HER2-targeted therapy. CellSearch system was applied as a reference control.

RESULTS

Phenotyping of CTCs in HER2 positive AGC patients demonstrated that HER2⁺ CTCs could be effectively eliminated in response to HER2-targeted therapy. Karyotyping of CTCs indicated that distinct CTCs with different ploidies of chromosomes 8 in AGC patients correlated to either sensitivity or resistance of paclitaxel or cisplatin-based chemotherapy. Examination of the copy number of chromosome 8 in CTCs provides a potential approach for predicting chemotherapeutic efficacy and monitoring chemo-resistance.

CONCLUSIONS

Phenotyping and karyotyping of the enriched CTCs upon ploidy of chromosome 8 or HER2 expression is of clinical potential for monitoring chemo-resistance and evaluating therapeutic efficacy for AGC patients.

A novel method for downstream characterization of breast cancer circulating tumor cells following CellSearch isolation

Background

Enumeration of circulating tumor cells (CTCs) obtained from minimally invasive blood samples has been well established as a valuable monitoring tool in metastatic and early breast cancer, as well as in several other cancer types. The gold standard technology for detecting CTCs in blood against a backdrop of millions of leukocytes is the FDA-approved CellSearch system (Janssen Diagnostics), which relies on EpCAM-based immunomagnetic separation. Secondary characterization of these cells could enable treatment selection based on specific targets in these cells, as well as providing a real time window into the metastatic process and offering unique insights into tumor heterogeneity. The objective of this study was to develop a method for downstream characterization of CTCs following isolation with the CellSearch system.

Methods

An in vitro CTC model system focusing on clinically useful treatment predictive biomarkers in breast cancer, specifically the estrogen receptor α (ERα) and the human epidermal growth factor receptor 2 (HER2), was established using healthy donor blood spiked with breast cancer cell lines MCF7 (ERα⁺/HER2⁻) and SKBr3 (ERα⁻/HER2⁺). Following CTC isolation by CellSearch, the captured CTCs were further enriched and fixed on a microscope slide using the in-house-developed CTC-DropMount technique.

Results

The recovery rate of CTCs after CellSearch Profile analysis and CTC-DropMount was 87%. A selective and consistent triple-immunostaining protocol was optimized. Cells positive for DAPI, cytokeratin (CK) 8, 18 and 19, but negative for the leukocyte-specific marker CD45, were classified as CTCs and subsequently analyzed for ERα and HER2 expression. The method was verified in breast cancer patient samples, thus demonstrating its clinical relevance.

Conclusions

Our results show that it is possible to ascertain the status of important predictive biomarkers expressed in breast cancer CTCs using the newly developed CTC-DropMount technique. Downstream characterization of multiple biomarkers using a standard fluorescence microscope demonstrates that important clinical and biological information may be obtained from a single patient blood sample following either CellSearch epithelial or profile analyses.

Trial registration

Clinical Trials NCT01322893

Androgen receptor expression in circulating tumour cells from castration-resistant prostate cancer patients treated with novel endocrine agents

BACKGROUND

Abiraterone and enzalutamide are novel endocrine treatments that abrogate androgen receptor (AR) signalling in castration-resistant prostate cancer (CRPC). Here, we developed a circulating tumour cells (CTCs)-based assay to evaluate AR expression in real-time in CRPC and investigated nuclear AR expression in CTCs in patients treated with enzalutamide and abiraterone.

METHODS

CTCs were captured and characterised using the CellSearch system. An automated algorithm to identify CTCs and quantify AR expression was employed. The primary aim was to evaluate the association between CTC AR expression and prior treatment with abiraterone or enzalutamide.

RESULTS

AR expression in CTCs was evaluated in 94 samples from 48 metastatic CRPC patients. We observed large intra-patient heterogeneity of AR expression in CTCs. Prior exposure to abiraterone or enzalutamide was not associated with a change in CTCs AR expression (median intensity and distribution of AR-positive classes). In support of this, we also confirmed maintained nuclear AR expression in tissue samples collected after progression on abiraterone. AR staining also identified additional AR-positive CD45-negative circulating cells that were CK-negative/weak and therefore missed using standard protocols. The number of these events correlated with traditional CTCs and was associated with worse outcome on univariate analysis.

CONCLUSIONS

We developed a non-invasive method to monitor AR nuclear expression in CTCs. Our studies confirm nuclear AR expression in CRPC patients progressing on novel endocrine treatments. Owing to the significant heterogeneity of AR expression in CTCs, studies in larger cohorts of patients are required to identify associations with outcome.

Circulating tumor cells: a multifunctional biomarker

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

Dormancy in solid tumors: implications for prostate cancer

In cancer dormancy, residual tumor cells persist in a patient with no apparent clinical symptoms, only to potentially become clinically relevant at a later date. In prostate cancer (PCa), the primary tumor is often removed and many patients experience a prolonged period (>5 years) with no evidence of disease before recurrence. These characteristics make PCa an excellent candidate for the study of tumor cell dormancy. However, the mechanisms that constitute PCa dormancy have not been clearly defined. Additionally, the definition of tumor cell dormancy varies in the literature. Therefore, we have separated tumor cell dormancy in this review into three categories: (a) micrometastatic dormancy--a group of tumor cells that cannot increase in number due to a restrictive proliferation/apoptosis equilibrium. (b) Angiogenic dormancy--a group of tumor cells that cannot expand beyond the formation of a micrometastasis due to a lack of angiogenic potential. (c) Conditional dormancy--an individual cell or a very small number of cells that cannot proliferate without the appropriate cues from the microenvironment, but do not require angiogenesis to do so. This review aims to identify currently known markers, mechanisms, and models of tumor dormancy, in particular as they relate to PCa, and highlight current opportunities for advancement in our understanding of clinical cancer dormancy.

Circulating tumor cells and circulating tumor DNA for precision medicine: dream or reality?

Next-generation sequencing studies have provided further evidence to support the notion that cancer is a disease characterized by Darwinian evolution. Today, we often fail to capture this evolution and treatment decisions, even in the metastatic setting, are often based on analysis of primary tumor diagnosed years ago. Currently, this is considered a major reason for treatment failures in cancer care. Recent technological advances in the detection and characterization of circulating tumor cells and circulating tumor DNA might address this and allow for treatment tailoring based on real-time monitoring of tumor evolution. In this review, we summarize the most important recent findings in the field, focusing on challenges and opportunities in moving these tools forward in clinical practice.