A Fully Automated and Integrated Microfluidic System for Efficient CTC Detection and Its Application in Hepatocellular Carcinoma Screening and Prognosis

Interfacial engineering for biomolecule immobilisation in microfluidic devices

Microfluidic devices are used for various applications in biology and medicine. From on-chip modelling of human organs for drug screening and fast and straightforward point-of-care (POC) detection of diseases to sensitive biochemical analysis, these devices can be custom-engineered using low-cost techniques. The microchannel interface is essential for these applications, as it is the interface of immobilised biomolecules that promote cell capture, attachment and proliferation, sense analytes and metabolites or provide enzymatic reaction readouts. However, common microfluidic materials do not facilitate the stable immobilisation of biomolecules required for relevant applications, making interfacial engineering necessary to attach biomolecules to the microfluidic surfaces. Interfacial engineering is performed through various immobilisation mechanisms and surface treatment techniques, which suitably modify the surface properties like chemistry and energy to obtain robust biomolecule immobilisation and long-term storage stability suitable for the final application. In this review, we provide an overview of the status of interfacial engineering in microfluidic devices, covering applications, the role of biomolecules, their immobilisation pathways and the influence of microfluidic materials. We then propose treatment techniques to optimise performance for various biological and medical applications and highlight future areas of development.

Detection, significance and potential utility of circulating tumor cells in clinical practice in breast cancer (Review)

Although advances in diagnostic techniques, new therapeutic strategies and personalization of breast cancer (BC) care have improved the survival for a number of patients, BC remains a major cause of morbidity and mortality for women. The study of circulating tumor cells (CTCs) has significant potential in translational oncology since these cells represent promising biomarkers throughout the entire course of BC in patients. CTCs also have notable prognostic value in early BC as well as metastatic BC. Based on current knowledge, it seems that the dynamics of CTCs that change during therapy reflect therapy response, and CTCs could serve as a tool for risk stratification and real-time monitoring of treatment in patients with BC. The question of how to use this information in everyday clinical practice and how this information can guide or change therapy to affect the clinical outcome of patients with BC remains unanswered. The present review aims to discuss current completed and ongoing trials that have been designed to demonstrate the clinical significance of CTCs, offer insights into treatment efficacy and assess CTC utility, facilitating their implementation in the routine management of patients with BC.

Circulating tumor cells in pancreatic cancer: more than liquid biopsy

Circulating tumor cells (CTCs) are tumor cells that slough off the primary lesions and extravasate into the bloodstream. By forming CTC clusters and interacting with other circulating cells (platelets, NK cells, macrophage, etc.), CTCs are able to survive in the circulatory system of tumor patients and colonize to metastatic organs. In recent years, the potential of CTCs in diagnosis, prognostic assessment, and individualized therapy of various types of tumors has been gradually explored, while advances in biotechnology have made it possible to extract CTCs from patient blood samples. These biological features of CTCs provide us with new insights into cancer vulnerabilities. With the advent of new immunotherapies and personalized medicines, disrupting the heterotypical interaction between CTCs and circulatory cells as well as direct CTCs targeting hold great promise. Pancreatic cancer (PC) is one of the most malignant cancers, in part because of early metastasis, difficult diagnosis, and limited treatment options. Although there is significant potential for CTCs as a biomarker to impact PC from diagnosis to therapy, there still remain a number of challenges to the routine implementation of CTCs in the clinical management of PC. In this review, we summed up the progress made in understanding biological characteristics and exceptional technological advances of CTCs and provided insight into exploiting these developments to design future clinical tools for improving the diagnosis and treatment of PC.

ECL cytosensor for sensitive and label-free detection of circulating tumor cells based on hierarchical flower-like gold microstructures

The development of sensitive and efficient cell sensing strategies to detect circulating tumor cells (CTCs) in peripheral blood is crucial for the early diagnosis and prognostic assessment of cancer clinical treatment. Herein, an array of hierarchical flower-like gold microstructures (HFGMs) with anisotropic nanotips was synthesized by a simple electrodeposition method and used as a capture substrate to construct an ECL cytosensor based on the specific recognition of target cells by aptamers. The complex topography of the HFGMs array not only catalyzed the enhancement of ECL signals, but also induced the cells to generate more filopodia, improving the capture efficiency and shortening the capture time. The effect of topographic roughness on cell growth and adhesion propensity was also investigated, while the cell capture efficiency was proposed to be an important indicator affecting the accuracy of the ECL cytosensor. In addition, the capture of cells on the electrode surface increased the steric hindrance, which caused ECL signal changes in the Ru(bpy)32+ and TPrA system, realizing the quantitative detection of MCF-7 cells. The detection range of the sensor was from 102 to 106 cells mL-1 and the detection limit was 18 cells mL-1. The proposed detection method avoids the process of separation, labeling and counting, which has great potential for sensitive detection in clinical applications.

Recent advances in nano/microfluidics-based cell isolation techniques for cancer diagnosis and treatments

Miniaturization has improved significantly in the recent decade, which has enabled the development of numerous microfluidic systems. Microfluidic technologies have shown great potential for separating desired cells from heterogeneous samples, as they offer benefits such as low sample consumption, easy operation, and high separation accuracy. Microfluidic cell separation approaches can be classified into physical (label-free) and biological (labeled) methods based on their working principles. Each method has remarkable and feasible benefits for the purposes of cancer detection and therapy, as well as the challenges that we have discussed in this article. In this review, we present the recent advances in microfluidic cell sorting techniques that incorporate both physical and biological aspects, with an emphasis on the methods by which the cells are separated. We first introduce and discuss the biological cell sorting techniques, followed by the physical cell sorting techniques. Additionally, we explore the role of microfluidics in drug screening, drug delivery, and lab-on-chip (LOC) therapy. In addition, we discuss the challenges and future prospects of integrated microfluidics for cell sorting.

Liquid biopsy for gastric cancer: Techniques, applications, and future directions

After the study of circulating tumor cells in blood through liquid biopsy (LB), this technique has evolved to encompass the analysis of multiple materials originating from the tumor, such as nucleic acids, extracellular vesicles, tumor-educated platelets, and other metabolites. Additionally, research has extended to include the examination of samples other than blood or plasma, such as saliva, gastric juice, urine, or stool. LB techniques are diverse, intricate, and variable. They must be highly sensitive, and pre-analytical, patient, and tumor-related factors significantly influence the detection threshold, diagnostic method selection, and potential results. Consequently, the implementation of LB in clinical practice still faces several challenges. The potential applications of LB range from early cancer detection to guiding targeted therapy or immunotherapy in both early and advanced cancer cases, monitoring treatment response, early identification of relapses, or assessing patient risk. On the other hand, gastric cancer (GC) is a disease often diagnosed at advanced stages. Despite recent advances in molecular understanding, the currently available treatment options have not substantially improved the prognosis for many of these patients. The application of LB in GC could be highly valuable as a non-invasive method for early diagnosis and for enhancing the management and outcomes of these patients. In this comprehensive review, from a pathologist's perspective, we provide an overview of the main options available in LB, delve into the fundamental principles of the most studied techniques, explore the potential utility of LB application in the context of GC, and address the obstacles that need to be overcome in the future to make this innovative technique a game-changer in cancer diagnosis and treatment within clinical practice.

An integrated microfluidic system for automatic detection of cholangiocarcinoma cells from bile

Cholangiocarcinoma (CCA) is an aggressive cancer that originates from the epithelial cells lining the bile ducts. Due to its location deep within the body and nonspecific symptoms in the early stages, it is often diagnosed at the advanced stage, thus leading to worse prognosis. Circulating tumor cells within liquid biopsies (i.e. blood) have been considered as promising biomarkers for CCA diagnosis, though current methods for profiling them are not satisfactory in terms of sensitivity and specificity. Herein we developed a new cancer cell probing and immuno-tracking assay known as "CAPTURE", which was performed on an integrated microfluidic system (IMS) to automate CCA diagnosis from bile with a sample amount of only 1 mL. The assay utilized magnetic beads surface-coated with two affinity reagents, a nucleic acid aptamer (HN16) and a glycosaminoglycan (SCH 45-mix), for capturing cancer cells in bile; the "gold standard" anti-epithelial cell adhesion molecule was used as a comparison. In a single-blind test of 54 CCA-positive (+) and 102 CCA-negative (-) clinical samples, sensitivities and specificities of 96 and 80%, respectively, were documented with the CAPTURE assay on-bench. An IMS composed of a centrifugal module for sample pretreatment and a CAPTURE module for cell capture and staining was integrated with a new "vertical integration module" for detecting cancer cells from bile without human intervention. Furthermore, a novel micro-tier structure within the centrifugal module was designed to block passage of gallbladder stones with diameters >1 mm, thereby preventing their interference during the subsequent CAPTURE assay. Improved sensitivity and specificity (100 & 83%, respectively) by using three affinity reagents were achieved on the IMS when using 26 clinical bile samples, confirming its clinical bio-applicability for CCA diagnosis. This approach could be therefore used for early-stage CCA diagnostics, ideally enabling effective treatment, as well as reducing potential for relapse.

3D Printed Nanosensors for Cancer Diagnosis: Advances and Future Perspective

Cancer is the leading cause of mortality worldwide, requiring continuous advancements in diagnosis and treatment. Traditional methods often lack sensitivity and specificity, leading to the need for new methods. 3D printing has emerged as a transformative tool in cancer diagnosis, offering the potential for precise and customizable nanosensors. These advancements are critical in cancer research, aiming to improve early detection and monitoring of tumors. In current times, the usage of the 3D printing technique has been more prevalent as a flexible medium for the production of accurate and adaptable nanosensors characterized by exceptional sensitivity and specificity. The study aims to enhance early cancer diagnosis and prognosis by developing advanced 3D-printed nanosensors using 3D printing technology. The research explores various 3D printing techniques, design strategies, and functionalization strategies for cancer-specific biomarkers. The integration of these nanosensors with detection modalities like fluorescence, electrochemical, and surface-enhanced Raman spectroscopy is also evaluated. The study explores the use of inkjet printing, stereolithography, and fused deposition modeling to create nanostructures with enhanced performance. It also discusses the design and functionalization methods for targeting cancer indicators. The integration of 3D-printed nanosensors with multiple detection modalities, including fluorescence, electrochemical, and surface-enhanced Raman spectroscopy, enables rapid and reliable cancer diagnosis. The results show improved sensitivity and specificity for cancer biomarkers, enabling early detection of tumor indicators and circulating cells. The study highlights the potential of 3D-printed nanosensors to transform cancer diagnosis by enabling highly sensitive and specific detection of tumor biomarkers. It signifies a pivotal step forward in cancer diagnostics, showcasing the capacity of 3D printing technology to produce advanced nanosensors that can significantly improve early cancer detection and patient outcomes.

Circulating Tumor Cells as a Promising Tool for Early Detection of Hepatocellular Carcinoma

Liver cancer is a significant contributor to the cancer burden, and its incidence rates have recently increased in almost all countries. Hepatocellular carcinoma (HCC) is the most common type of primary liver cancer and is the second leading cause of cancer-related deaths worldwide. Because of the late diagnosis and lack of efficient therapeutic modality for advanced stages of HCC, the death rate continues to increase by ~2-3% per year. Circulating tumor cells (CTCs) are promising tools for early diagnosis, precise prognosis, and follow-up of therapeutic responses. They can be considered to be an innovative biomarker for the early detection of tumors and targeted molecular therapy. In this review, we briefly discuss the novel materials and technologies applied for the practical isolation and detection of CTCs in HCC. Also, the clinical value of CTC detection in HCC is highlighted.

Integrated "lab-on-a-chip" microfluidic systems for isolation, enrichment, and analysis of cancer biomarkers

The liquid biopsy has garnered considerable attention as a complementary clinical tool for the early detection, molecular characterization and monitoring of cancer over the past decade. In contrast to traditional solid biopsy techniques, liquid biopsy offers a less invasive and safer alternative for routine cancer screening. Recent advances in microfluidic technologies have enabled handling of liquid biopsy-derived biomarkers with high sensitivity, throughput, and convenience. The integration of these multi-functional microfluidic technologies into a 'lab-on-a-chip' offers a powerful solution for processing and analyzing samples on a single platform, thereby reducing the complexity, bio-analyte loss and cross-contamination associated with multiple handling and transfer steps in more conventional benchtop workflows. This review critically addresses recent developments in integrated microfluidic technologies for cancer detection, highlighting isolation, enrichment, and analysis strategies for three important sub-types of cancer biomarkers: circulating tumor cells, circulating tumor DNA and exosomes. We first discuss the unique characteristics and advantages of the various lab-on-a-chip technologies developed to operate on each biomarker subtype. This is then followed by a discussion on the challenges and opportunities in the field of integrated systems for cancer detection. Ultimately, integrated microfluidic platforms form the core of a new class of point-of-care diagnostic tools by virtue of their ease-of-operation, portability and high sensitivity. Widespread availability of such tools could potentially result in more frequent and convenient screening for early signs of cancer at clinical labs or primary care offices.

Novel method for highly multiplexed gene expression profiling of circulating tumor cells (CTCs) captured from the blood of women with metastatic breast cancer

BACKGROUND

Enumeration of circulating tumor cells (CTCs) has proven clinical significance for monitoring patients with metastatic cancers. Multiplexed gene expression profiling of CTCs is a potential tool for assessing disease status and monitoring treatment response. The Parsortix^® technology enables the capture and harvest of CTCs from blood based on cell size and deformability. The HyCEAD^™ (Hybrid Capture Enrichment Amplification and Detection) assay enables simultaneous amplification of short amplicons for up to 100 mRNA targets, and the Ziplex^™ instrument quantifies the amplicons for highly sensitive gene expression profiling down to single cell levels. The aim of the study was to functionally assess this system.

METHODS

The HyCEAD/Ziplex platform was used to quantify the expression levels for 72 genes using as little as 20 pg of total RNA or a single cultured tumor cell. Assay performance was evaluated using cells or total RNA spiked into Parsortix harvests of healthy donor blood. The assay was also evaluated using total RNA obtained from Parsortix harvests of blood from metastatic breast cancer (MBC) patients or healthy volunteers (HVs).

RESULTS

Using genes with low expression in WBC RNA and/or in unspiked Parsortix harvests from HVs, the assay distinguished between the different breast cancer and ovarian cancer cell lines with as little as 20 pg of total RNA (equivalent to a single cell) in the presence of 1 ng of WBC RNA. Single cultured cells spiked into Parsortix harvests from 10 mL of HV blood were also detected and distinguished from each other. CVs from repeatability experiments were less than 20%. Hierarchical clustering of clinical samples differentiated most MBC patients from HVs.

CONCLUSION

HyCEAD/Ziplex provided sensitive quantification of expression of 72 genes from 20 pg of total RNA from cultured tumor cell lines or from single cultured tumor cells spiked into lysates from Parsortix harvests of HV blood. The HyCEAD/Ziplex platform enables the quantification of selected genes in the presence of residual nucleated blood cells in Parsortix harvests. The HyCEAD/Ziplex platform is an effective tool for multiplexed molecular characterization of mRNA in small numbers of tumor cells harvested from blood.

A Microfluidic System for Detecting Tumor Cells Based on Biomarker Hexaminolevulinate (HAL): Applications in Pleural Effusion

Malignant pleural effusion is a common clinical problem, which often occurs in cases of malignant tumors, especially in lung cancer. In this paper, a pleural effusion detection system based on a microfluidic chip, combined with specific tumor biomarker, hexaminolevulinate (HAL), used to concentrate and identify tumor cells in pleural effusion was reported. The lung adenocarcinoma cell line A549 and mesothelial cell line Met-5A were cultured as the tumor cells and non-tumor cells, respectively. The optimum enrichment effect was achieved in the microfluidic chip when the flow rates of cell suspension and phosphate-buffered saline achieved 2 mL/h and 4 mL/h, respectively. At the optimal flow rate, the proportion of A549 increased from 28.04% to 70.01% due to the concentration effect of the chip, indicating that tumor cells could be enriched by a factor of 2.5 times. In addition, HAL staining results revealed that HAL can be used to identify tumor cells and non-tumor cells in chip and clinical samples. Additionally, the tumor cells obtained from the patients diagnosed with lung cancer were confirmed to be captured in the microfluidic chip, proving the validity of the microfluidic detection system. This study preliminarily demonstrates the microfluidic system is a promising method with which to assist clinical detection in pleural effusion.

Lab-on-a-chip systems for cancer biomarker diagnosis

Lab-on-a-chip (LOC) or micro total analysis system is one of the microfluidic technologies defined as the adaptation, miniaturization, integration, and automation of analytical laboratory procedures into a single instrument or "chip". In this article, we review developments over the past five years in the application of LOC biosensors for the detection of different types of cancer. Microfluidics encompasses chemistry and biotechnology skills and has revolutionized healthcare diagnosis. Superior to traditional cell culture or animal models, microfluidic technology has made it possible to reconstruct functional units of organs on chips to study human diseases such as cancer. LOCs have found numerous biomedical applications over the past five years, including integrated bioassays, cell analysis, metabolomics, drug discovery and delivery systems, tissue and organ physiology and disease modeling, and personalized medicine. This review provides an overview of the latest developments in microfluidic-based cancer research, with pros, cons, and prospects.

Circulating Biomarkers for the Early Diagnosis and Management of Hepatocellular Carcinoma with Potential Application in Resource-Limited Settings

Hepatocellular carcinoma (HCC) is among the world's third most lethal cancers. In resource-limited settings (RLS), up to 70% of HCCs are diagnosed with limited curative treatments at an advanced symptomatic stage. Even when HCC is detected early and resection surgery is offered, the post-operative recurrence rate after resection exceeds 70% in five years, of which about 50% occur within two years of surgery. There are no specific biomarkers addressing the surveillance of HCC recurrence due to the limited sensitivity of the available methods. The primary goal in the early diagnosis and management of HCC is to cure disease and improve survival, respectively. Circulating biomarkers can be used as screening, diagnostic, prognostic, and predictive biomarkers to achieve the primary goal of HCC. In this review, we highlighted key circulating blood- or urine-based HCC biomarkers and considered their potential applications in resource-limited settings, where the unmet medical needs of HCC are disproportionately highly significant.

Cancer metastasis chemoprevention prevents circulating tumour cells from germination

The war against cancer traces back to the signature event half-a-century ago when the US National Cancer Act was signed into law. The cancer crusade costs trillions with disappointing returns, teasing the possibility of a new breakthrough. Cure for cancer post-metastases still seems tantalisingly out of reach. Once metastasized, cancer-related death is extremely difficult, if not impossible, to be reversed. Here we present cancer pre-metastasis chemoprevention strategy that can prevent circulating tumour cells (CTCs) from initiating metastases safely and effectively, and is disparate from the traditional cancer chemotherapy and cancer chemoprevention. Deep learning of the biology of CTCs and their disseminating organotropism, complexity of their adhesion to endothelial niche reveals that if the adhesion of CTCs to their metastasis niche (the first and the most important part in cancer metastatic cascade) can be pharmaceutically interrupted, the lethal metastatic cascade could be prevented from getting initiated. We analyse the key inflammatory and adhesive factors contributing to CTC adhesion/germination, provide pharmacological fundamentals for abortifacients to intervene CTC adhesion to the distant metastasis sites. The adhesion/inhibition ratio (AIR) is defined for selecting the best cancer metastasis chemopreventive candidates. The successful development of such new therapeutic modalities for cancer metastasis chemoprevention has great potential to revolutionise the current ineffective post-metastasis treatments.

Uncovering the Heterogeneity and Clinical Relevance of Circulating Tumor-Initiating Cells in Hepatocellular Carcinoma Using an Integrated Immunomagnetic-Microfluidic Platform

Circulating tumor-initiating cells (CTICs) with stem cell-like properties play pivotal roles in tumor metastasis and recurrence. However, little is known about the biology and clinical relevance of CTICs in hepatocellular carcinoma (HCC). Here, we investigated the molecular heterogeneity and clinical relevance of CTICs in HCC using a novel integrated immunomagnetic-microfluidic platform (iMAC). We constructed the iMAC and evaluated its ability to detect CTICs using a series of spiked cell experiments. A four-channel microfluidic chip was applied to investigate the composition of CTICs in patients with primary and recurrent HCC utilizing microbeads labeled with one of four stem-related markers: epithelial cell adhesion molecule (EpCAM), CD133, CD90, and CD24. The dynamic changes of these four CTIC subsets were serially monitored during treatment courses. Finally, single-cell RNA profiling was used to reveal the molecular characteristics of the four CTIC subsets. The iMAC platform detected significantly more EpCAM+ CTICs in the blood samples from 33 HCC patients than the FDA-approved CellSearch system (0.92 ± 0.94 vs 0.23 ± 0.36, P < 0.001). The number of EpCAM+ CTICs (≥0.75/mL) detected by iMAC was a predictor of early recurrence (P = 0.007). The distinct stem-related markers' expression of CTICs could distinguish primary HCC, recurrent HCC, and TACE-resistant HCC. Single-cell transcriptional profiling proved the heterogeneity among individual CTICs and separated the four CTIC subsets into distinct phenotypes. Dissecting the heterogeneity of CTICs using the iMAC represents a novel and informative method for accurate CTIC detection and characterization. This innovative technology will enable more indepth cancer biology research and clinical cancer management than is currently available.

Detection of circulating tumor cells: opportunities and challenges

Circulating tumor cells (CTCs) are cells that shed from a primary tumor and travel through the bloodstream. Studying the functional and molecular characteristics of CTCs may provide in-depth knowledge regarding highly lethal tumor diseases. Researchers are working to design devices and develop analytical methods that can capture and detect CTCs in whole blood from cancer patients with improved sensitivity and specificity. Techniques using whole blood samples utilize physical prosperity, immunoaffinity or a combination of the above methods and positive and negative enrichment during separation. Further analysis of CTCs is helpful in cancer monitoring, efficacy evaluation and designing of targeted cancer treatment methods. Although many advances have been achieved in the detection and molecular characterization of CTCs, several challenges still exist that limit the current use of this burgeoning diagnostic approach. In this review, a brief summary of the biological characterization of CTCs is presented. We focus on the current existing CTC detection methods and the potential clinical implications and challenges of CTCs. We also put forward our own views regarding the future development direction of CTCs.

Three-Dimensional (3D) Printing in Cancer Therapy and Diagnostics: Current Status and Future Perspectives

Three-dimensional (3D) printing is a technique where the products are printed layer-by-layer via a series of cross-sectional slices with the exact deposition of different cell types and biomaterials based on computer-aided design software. Three-dimensional printing can be divided into several approaches, such as extrusion-based printing, laser-induced forward transfer-based printing systems, and so on. Bio-ink is a crucial tool necessary for the fabrication of the 3D construct of living tissue in order to mimic the native tissue/cells using 3D printing technology. The formation of 3D software helps in the development of novel drug delivery systems with drug screening potential, as well as 3D constructs of tumor models. Additionally, several complex structures of inner tissues like stroma and channels of different sizes are printed through 3D printing techniques. Three-dimensional printing technology could also be used to develop therapy training simulators for educational purposes so that learners can practice complex surgical procedures. The fabrication of implantable medical devices using 3D printing technology with less risk of infections is receiving increased attention recently. A Cancer-on-a-chip is a microfluidic device that recreates tumor physiology and allows for a continuous supply of nutrients or therapeutic compounds. In this review, based on the recent literature, we have discussed various printing methods for 3D printing and types of bio-inks, and provided information on how 3D printing plays a crucial role in cancer management.

Application of Microfluidics in Detection of Circulating Tumor Cells

Tumor metastasis is one of the main causes of cancer incidence and death worldwide. In the process of tumor metastasis, the isolation and analysis of circulating tumor cells (CTCs) plays a crucial role in the early diagnosis and prognosis of cancer patients. Due to the rarity and inherent heterogeneity of CTCs, there is an urgent need for reliable CTCs separation and detection methods in order to obtain valuable information on tumor metastasis and progression from CTCs. Microfluidic technology is increasingly used in various studies of CTCs separation, identification and characterization because of its unique advantages, such as low cost, simple operation, less reagent consumption, miniaturization of the system, rapid detection and accurate control. This paper reviews the research progress of microfluidic technology in CTCs separation and detection in recent years, as well as the potential clinical application of CTCs, looks forward to the application prospect of microfluidic technology in the treatment of tumor metastasis, and briefly discusses the development prospect of microfluidic biosensor.

Engineering complexity in human tissue models of cancer

Major progress in the understanding and treatment of cancer have tremendously improved our knowledge of this complex disease and improved the length and quality of patients' lives. Still, major challenges remain, in particular with respect to cancer metastasis which still escapes effective treatment and remains responsible for 90% of cancer related deaths. In recent years, the advances in cancer cell biology, oncology and tissue engineering converged into the engineered human tissue models of cancer that are increasingly recapitulating many aspects of cancer progression and response to drugs, in a patient-specific context. The complexity and biological fidelity of these models, as well as the specific questions they aim to investigate, vary in a very broad range. When selecting and designing these experimental models, the fundamental question is "how simple is complex enough" to accomplish a specific goal of cancer research. Here we review the state of the art in developing and using the human tissue models in cancer research and developmental drug screening. We describe the main classes of models providing different levels of biological fidelity and complexity, discuss their advantages and limitations, and propose a framework for designing an appropriate model for a given study. We close by outlining some of the current needs, opportunities and challenges in this rapidly evolving field.

[Recent advances in isolation and detection of circulating tumor cells with a microfluidic system]

The isolation and analysis of circulating tumor cells (CTCs) is an important issue in tumor research. CTCs in peripheral blood, which are important biomarkers of liquid biopsy, are closely related to the occurrence of cancer and are used to monitor the effect of treatment on cancer patients. However, the number of CTCs in the blood samples of cancer patients is very low, usually being present at only 0-10 CTCs/mL. Therefore, prior to the detection of CTCs, it is important to preprocess clinical blood samples for efficient separation and enrichment. With the advantages of low sample consumption, high separation efficiency, ease of automation and integration, microfluidic chips can be a suitable platform for the isolation of CTCs. In the last few years, CTC separation and detection using microfluidic chips have developed rapidly, and a variety of detection methods have been developed. According to the technical principle used, microfluidics for CTC separation can be divided into biological property-based methods and physical property-based methods. The biological property-based methods mainly depend on the interaction between the antigen and antibody, or the specific binding of the aptamer and target. These methods have high selectivity but low efficiency and recovery rates. Physical separation is based on the physical properties of CTCs such as their size, density, and dielectric properties. For example, CTCs can be blocked or captured by the microstructure in the channels of microfluidic chips, sorted by external physical fields (acoustic, electrical, magnetic), or screened by micro-scale hydrodynamics. Physical property-based methods generally have a higher flux but lower separation purity. However, the advantages of biological property-based methods and physical property-based methods can be integrated to provide microfluidic chips having better separation performance. In addition to the direct positive enrichment of CTCs, a negative enrichment strategy can also be adopted. The influence of direct screening on the activity of CTCs can be avoided by selectively removing white blood cells. In this paper, recent advances in microfluidics utilized in the isolation of CTCs, including physical and immune methods and positive and negative enrichment, are reviewed. We summarized the technical principles, detection methods, and research progress in CTC separation and detection using microfluidic chips. Developing trends in microfluidics for CTC separation and analysis are also discussed.

Circulating tumor cells: biology and clinical significance

Circulating tumor cells (CTCs) are tumor cells that have sloughed off the primary tumor and extravasate into and circulate in the blood. Understanding of the metastatic cascade of CTCs has tremendous potential for the identification of targets against cancer metastasis. Detecting these very rare CTCs among the massive blood cells is challenging. However, emerging technologies for CTCs detection have profoundly contributed to deepening investigation into the biology of CTCs and have facilitated their clinical application. Current technologies for the detection of CTCs are summarized herein, together with their advantages and disadvantages. The detection of CTCs is usually dependent on molecular markers, with the epithelial cell adhesion molecule being the most widely used, although molecular markers vary between different types of cancer. Properties associated with epithelial-to-mesenchymal transition and stemness have been identified in CTCs, indicating their increased metastatic capacity. Only a small proportion of CTCs can survive and eventually initiate metastases, suggesting that an interaction and modulation between CTCs and the hostile blood microenvironment is essential for CTC metastasis. Single-cell sequencing of CTCs has been extensively investigated, and has enabled researchers to reveal the genome and transcriptome of CTCs. Herein, we also review the clinical applications of CTCs, especially for monitoring response to cancer treatment and in evaluating prognosis. Hence, CTCs have and will continue to contribute to providing significant insights into metastatic processes and will open new avenues for useful clinical applications.