The Discordance of Gene Mutations between Circulating Tumor Cells and Primary/Metastatic Tumor

A Molecular Voyage: Multiomics Insights into Circulating Tumor Cells

Circulating tumor cells (CTCs) play a pivotal role in metastasis, the leading cause of cancer-associated death. Recent improvements of CTC isolation tools, coupled with a steady development of multiomics technologies at single-cell resolution, have enabled an extensive exploration of CTC biology, unlocking insights into their molecular profiles. A detailed molecular portrait requires CTC interrogation across various levels encompassing genomic, epigenetic, transcriptomic, proteomic and metabolic features. Here, we review how state-of-the-art multiomics applied to CTCs are shedding light on how cancer spreads. Further, we highlight the potential implications of CTC profiling for clinical applications aimed at enhancing cancer diagnosis and treatment.

SIGNIFICANCE

Exploring the complexity of cancer progression through cutting-edge multiomics studies holds the promise of uncovering novel aspects of cancer biology and identifying therapeutic vulnerabilities to suppress metastasis.

Correlation between KRAS Mutation and CTLA-4 mRNA Expression in Circulating Tumour Cells: Clinical Implications in Colorectal Cancer

Combination strategies of KRAS inhibition with immunotherapy in treating advanced or recurrent colorectal carcinoma (CRC) may need to be assessed in circulating tumour cells (CTCs) to achieve better clinical outcomes. This study aimed to investigate the genomic variations of KRAS in CTCs and matched CRC tissues and compared mRNA expression of KRAS and CTLA-4 between wild-type and KRAS-mutated CTCs and CRC tissues. Clinicopathological correlations were also compared. Six known mutations of KRAS were identified at both codon 12 and codon 13 (c.35G>T/G12V, c.35G>A7/G12D, c.35G>C/G12A, c.34G>A/G12S, c.38G>C/G13A, and c.38G>A/G13D). Three CTC samples harboured the identified mutations (16.7%; 3/18), while fifteen matched primary tumour tissues (65.2%, 15/23) showed the mutations. CTCs harbouring the KRAS variant were different from matched CRC tissue. All the mutations were heterozygous. Though insignificant, CTLA-4 mRNA expression was higher in patients carrying KRAS mutations. Patients harbouring KRAS mutations in CTCs were more likely to have poorly differentiated tumours (p = 0.039) and with lymph node metastasis (p = 0.027) and perineural invasion (p = 0.014). KRAS mutations in CTCs were also significantly correlated with overall pathological stages (p = 0.027). These findings imply the genetic basis of KRAS with immunotherapeutic target molecules based on a real-time platform. This study also suggests the highly heterogeneous nature of cancer cells, which may facilitate the assessment of clonal dynamics across a single patient's disease.

Circulating tumour cells: The Good, the Bad and the Ugly

This review is an overview of the current knowledge regarding circulating tumour cells (CTCs), which are potentially the most lethal type of cancer cell, and may be a key component of the metastatic cascade. The clinical utility of CTCs (the "Good"), includes their diagnostic, prognostic, and therapeutic potential. Conversely, their complex biology (the "Bad"), including the existence of CD45+/EpCAM+ CTCs, adds insult to injury regarding their isolation and identification, which in turn hampers their clinical translation. CTCs are capable of forming microemboli composed of both non-discrete phenotypic populations such as mesenchymal CTCs and homotypic and heterotypic clusters which are poised to interact with other cells in the circulation, including immune cells and platelets, which may increase their malignant potential. These microemboli (the "Ugly") represent a prognostically important CTC subset, however, phenotypic EMT/MET gradients bring additional complexities to an already challenging situation.

Clinical Relevancy of Circulating Tumor Cells in Breast Cancer: Epithelial or Mesenchymal Characteristics, Single Cells or Clusters?

Metastatic breast cancer (MBC) is typically an incurable disease with high mortality rates; thus, early identification of metastatic features and disease recurrence through precise biomarkers is crucial. Circulating tumor cells (CTCs) consisting of heterogeneous subpopulations with different morphology and genetic, epigenetic, and gene expression profiles represent promising candidate biomarkers for metastatic potential. The experimentally verified role of epithelial-to-mesenchymal transition in cancer dissemination has not been clearly described in BC patients, but the stemness features of CTCs strongly contributes to metastatic potency. Single CTCs have been shown to be protected in the bloodstream against recognition by the immune system through impaired interactions with T lymphocytes and NK cells, while associations of heterotypic CTC clusters with platelets, leucocytes, neutrophils, tumor-associated macrophages, and fibroblasts improve their tumorigenic behavior. In addition to single CTC and CTC cluster characteristics, we reviewed CTC evaluation methods and clinical studies in early and metastatic BCs. The variable CTC tests were developed based on specific principles and strategies. However, CTC count and the presence of CTC clusters were shown to be most clinically relevant in existing clinical trials. Despite the known progress in CTC research and sampling of BC patients, implementation of CTCs and CTC clusters in routine diagnostic and treatment strategies still requires improvement in detection sensitivity and precise molecular characterizations, focused predominantly on the role of CTC clusters for their higher metastatic potency.

Circulating tumor cells from melanoma patients show phenotypic plasticity and metastatic potential in xenograft NOD.CB17 mice

Background

Innovative therapies have improved the overall survival in melanoma, although a high number of patients still experience disease progression or recurrence. Ex-vivo culture of circulating tumour cells (CTCs) represents a valuable laboratory resource for in-depth characterization of rare cell populations responsible for disease progression.

Methods

CTCs from patients with metastatic melanoma were in-vitro established. Their stemness was demonstrated by both phenotypic and genotypic assays, as well as by functional studies. Xenograft experiments in NOD.CB17 mice injected with CTCs from a single patient were completed. Data were analysed by Student’s test and results expressed as mean ± SEM.

Results

CTCs share the mutational profile with primary cells, an intermediate epithelial-mesenchymal transition (EMT) phenotype and high expression of the immunosuppressive factors. A subclonal CTC population exhibited stem cell properties as high aldehyde dehydrogenase 1 activity, melanosphere-forming ability, and expression of major stemness transcription factors. Xenograft experiments confirmed the CTC ability to generate melanoma in-vivo and revealed enhanced metastatic propensity.

Conclusions

CTCs play a relevant role in melanoma and may actively contribute to drive the disease progression and metastasis. Thus, they are a unique potential tool for pharmacogenomic studies to guide treatment strategies in advanced disease.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09829-1.

Circulating Exosome Cargoes Contain Functionally Diverse Cancer Biomarkers: From Biogenesis and Function to Purification and Potential Translational Utility

Although diagnostic and therapeutic treatments of cancer have tremendously improved over the past two decades, the indolent nature of its symptoms has made early detection challenging. Thus, inter-disciplinary (genomic, transcriptomic, proteomic, and lipidomic) research efforts have been focused on the non-invasive identification of unique "silver bullet" cancer biomarkers for the design of ultra-sensitive molecular diagnostic assays. Circulating tumor biomarkers, such as CTCs and ctDNAs, which are released by tumors in the circulation, have already demonstrated their clinical utility for the non-invasive detection of certain solid tumors. Considering that exosomes are actively produced by all cells, including tumor cells, and can be found in the circulation, they have been extensively assessed for their potential as a source of circulating cell-specific biomarkers. Exosomes are particularly appealing because they represent a stable and encapsulated reservoir of active biological compounds that may be useful for the non-invasive detection of cancer. T biogenesis of these extracellular vesicles is profoundly altered during carcinogenesis, but because they harbor unique or uniquely combined surface proteins, cancer biomarker studies have been focused on their purification from biofluids, for the analysis of their RNA, DNA, protein, and lipid cargoes. In this review, we evaluate the biogenesis of normal and cancer exosomes, provide extensive information on the state of the art, the current purification methods, and the technologies employed for genomic, transcriptomic, proteomic, and lipidomic evaluation of their cargoes. Our thorough examination of the literature highlights the current limitations and promising future of exosomes as a liquid biopsy for the identification of circulating tumor biomarkers.

Consistency evaluation of lung adenocarcinoma tissue and circulating tumor cells related gene mutation detection based on multi-site immunomagnetic beads

This study was designed to investigate the feasibility of genetic testing using circulating tumor cells (CTCs) instead of tumor tissues in lung adenocarcinoma to break through its limitation. Separation system for epithelial cell adhesion molecule (EpCAM), epidermal growth factor receptor (EGFR), and Vimentin expressing CTCs was constructed and used to capture CTCs in the blood samples of 57 patients with lung adenocarcinoma. Genetic mutations of genes involved in targeted therapies were detected by next-generation sequencing (NGS) in tissues from these patients. Blood CTC samples with the gene mutations identified by tissue-NGS were selected and corresponding gene mutations were detected by Sanger sequencing. The specificity of the CTC separation system was 95.48% and the sensitivity was 90.85%. The average number of CTCs in the blood of patients with lung adenocarcinoma was 12.47/7.5 mL. Comparison of the tissue-NGS with the CTC-Sanger sequencing showed that the consistencies of genetic mutations of EGFR (n = 24), KRAS (n = 9), TP53 (n = 19), BRAF (n = 1), ERBB2 (n = 2), and PIK3CA (n = 3) were 92.31%, 75.00%, 86.36%, 50.00%, 66.67%, and 75.00%, with an overall consistency of 84.06%. The CTC separation system established in this study shows high specificity and sensitivity. CTCs can be used as a suitable alternative to tumor tissues that are difficult to obtain in clinical practice and overcome the difficulties in tumor tissue collection, which is of significance in guiding clinical medication and individualized treatment with significant clinical application value in terms of genetic testing for targeted therapies in tumor treatment.

Relevance of Circulating Tumor Cells as Predictive Markers for Cancer Incidence and Relapse

Shedding of cancer cells from the primary site or undetectable bone marrow region into the circulatory system, resulting in clinically overt metastasis or dissemination, is the hallmark of unfavorable invasive cancers. The shed cells remain in circulation until they extravasate to form a secondary metastatic lesion or undergo anoikis. The circulating tumor cells (CTCs) found as single cells or clusters carry a plethora of information, are acknowledged as potential biomarkers for predicting cancer prognosis and cancer progression, and are supposed to play key roles in determining tailored therapies for advanced diseases. With the advent of novel technologies that allow the precise isolation of CTCs, more and more clinical trials are focusing on the prognostic and predictive potential of CTCs. In this review, we summarize the role of CTCs as a predictive marker for cancer incidence, relapse, and response to therapy.

Physical Forces and Transient Nuclear Envelope Rupture during Metastasis: The Key for Success?

Simple Summary

Metastasis is the process that allows the seeding of tumor cells in a new organ. The migration and invasion of cancer cells involves the pulling, pushing, and squeezing of cells through narrow spaces and pores. Tumor cells need to cross several physical barriers, such as layers of basement membranes as well as the endothelium wall during the way in and out of the blood stream, to reach the new organ. The aim of this review is to highlight the role of physical compression in the success of metastasis. We will especially focus on nuclear squeezing and nuclear envelope rupture and explain how they can actively participate in the creation of genomic heterogeneity as well as supporting metastasis growth.

Abstract

During metastasis, invading tumor cells and circulating tumor cells (CTC) face multiple mechanical challenges during migration through narrow pores and cell squeezing. However, little is known on the importance and consequences of mechanical stress for tumor progression and success in invading a new organ. Recently, several studies have shown that cell constriction can lead to nuclear envelope rupture (NER) during interphase. This loss of proper nuclear compartmentalization has a profound effect on the genome, being a key driver for the genome evolution needed for tumor progression. More than just being a source of genomic alterations, the transient nuclear envelope collapse can also support metastatic growth by several mechanisms involving the innate immune response cGAS/STING pathway. In this review we will describe the importance of the underestimated role of cellular squeezing in the progression of tumorigenesis. We will describe the complexity and difficulty for tumor cells to reach the metastatic site, detail the genomic aberration diversity due to NER, and highlight the importance of the activation of the innate immune pathway on cell survival. Cellular adaptation and nuclear deformation can be the key to the metastasis success in many unsuspected aspects.

Detection and clinical significance of circulating tumor cells in colorectal cancer

Histopathological examination (biopsy) is the "gold standard" for the diagnosis of colorectal cancer (CRC). However, biopsy is an invasive method, and due to the temporal and spatial heterogeneity of the tumor, a single biopsy cannot reveal the comprehensive biological characteristics and dynamic changes of the tumor. Therefore, there is a need for new biomarkers to improve CRC diagnosis and to monitor and treat CRC patients. Numerous studies have shown that "liquid biopsy" is a promising minimally invasive method for early CRC detection. A liquid biopsy mainly samples circulating tumor cells (CTCs), circulating tumor DNA (ctDNA), microRNA (miRNA) and extracellular vesicles (EVs). CTCs are malignant cells that are shed from the primary tumors and/or metastases into the peripheral circulation. CTCs carry information on both primary tumors and metastases that can reflect dynamic changes in tumors in a timely manner. As a promising biomarker, CTCs can be used for early disease detection, treatment response and disease progression evaluation, disease mechanism elucidation, and therapeutic target identification for drug development. This review will discuss currently available technologies for plasma CTC isolation and detection, their utility in the management of CRC patients and future research directions.

Chemo-specific designs for the enumeration of circulating tumor cells: advances in liquid biopsy

Advanced materials and chemo-specific designs at the nano/micrometer-scale have ensured revolutionary progress in next-generation clinically relevant technologies. For example, isolating a rare population of cells, like circulating tumor cells (CTCs) from the blood amongst billions of other blood cells, is one of the most complex scientific challenges in cancer diagnostics. The chemical tunability for achieving this degree of exceptional specificity for extra-cellular biomarker interactions demands the utility of advanced entities and multistep reactions both in solution and in the insoluble state. Thus, this review delineates the chemo-specific substrates, chemical methods, and structure-activity relationships (SARs) of chemical platforms used for isolation and enumeration of CTCs in advancing the relevance of liquid biopsy in cancer diagnostics and disease management. We highlight the synthesis of cell-specific, tumor biomarker-based, chemo-specific substrates utilizing functionalized linkers through chemistry-based conjugation strategies. The capacity of these nano/micro substrates to enhance the cell interaction specificity and efficiency with the targeted tumor cells is detailed. Furthermore, this review accounts for the importance of CTC capture and other downstream processes involving genotypic and phenotypic CTC analysis in real-time for the detection of the early onset of metastases progression and chemotherapy treatment response, and for monitoring progression free-survival (PFS), disease-free survival (DFS), and eventually overall survival (OS) in cancer patients.

Mesenchymal Characteristics and Predictive Biomarkers on Circulating Tumor Cells for Therapeutic Strategy

Metastasis-related events are the primary cause of cancer-related deaths, and circulating tumor cells (CTCs) have a pivotal role in metastatic relapse. CTCs include a variety of subtypes with different functional characteristics. Interestingly, the epithelial-mesenchymal transition (EMT) markers expressed in CTCs are strongly associated with poor clinical outcome and related to the acquisition of circulating tumor stem cell (CTSC) features. Recent studies have revealed the existence of CTC clusters, also called circulating tumor microemboli (CTM), which have a high metastatic potential. In this review, we present current opinions regarding the clinical significance of CTCs and CTM with a mesenchymal phenotype as clinical surrogate markers, and we summarize the therapeutic strategy according to phenotype characterization of CTCs in various types of cancers for future precision medicine.

The Polemic Diagnostic Role of TP53 Mutations in Liquid Biopsies from Breast, Colon and Lung Cancers

Being minimally invasive and thus allowing repeated measures over time, liquid biopsies are taking over traditional solid biopsies in certain circumstances such as those for unreachable tumors, very early stages or treatment monitoring. However, regarding TP53 mutation status analysis, liquid biopsies have not yet substituted tissue samples, mainly due to the lack of concordance between the two types of biopsies. This needs to be examined in a study-dependent manner, taking into account the particular type of liquid biopsy analyzed, that is, circulating tumor cells (CTCs) or cell-free DNA (cfDNA), its involvement in the tumor biology and evolution and, finally, the technology used to analyze each biopsy type. Here, we review the main studies analyzing TP53 mutations in either CTCs or cfDNA in the three more prevalent solid tumors: breast, colon and lung cancers. We evaluate the correlation for mutation status between liquid biopsies and tumor tissue, suggesting possible sources of discrepancies, as well as evaluating the clinical utility of using liquid biopsies for the analysis of TP53 mutation status and the future actions that need to be undertaken to make liquid biopsy analysis a reality for the evaluation of TP53 mutations.

Heterogeneity of Circulating Tumor Cells in Breast Cancer: Identifying Metastatic Seeds

Metastasis being the main cause of breast cancer (BC) mortality represents the complex and multistage process. The entrance of tumor cells into the blood vessels and the appearance of circulating tumor cells (CTCs) seeding and colonizing distant tissues and organs are one of the key stages in the metastatic cascade. Like the primary tumor, CTCs are extremely heterogeneous and presented by clusters and individual cells which consist of phenotypically and genetically distinct subpopulations. However, among this diversity, only a small number of CTCs is able to survive in the bloodstream and to form metastases. The identification of the metastasis-initiating CTCs is believed to be a critical issue in developing therapeutic strategies against metastatic disease. In this review, we summarize the available literature addressing morphological, phenotypic and genetic heterogeneity of CTCs and the molecular makeup of specific subpopulations associated with BC metastasis. Special attention is paid to the need for in vitro and in vivo studies to confirm the tumorigenic and metastatic potential of metastasis-associating CTCs. Finally, we consider treatment approaches that could be effective to eradicate metastatic CTCs and to prevent metastasis.

Circulating Tumor Cells in Early and Advanced Breast Cancer; Biology and Prognostic Value

Breast cancer metastasis is the leading cause of cancer deaths in women and is difficult to combat due to the long periods in which disseminated cells retain a potential to be re-activated and start the relapse. Assessing the number and molecular profile of circulating tumor cells (CTCs) in breast cancer patients, especially in early breast cancer, should help in identifying the possibility of relapse in time for therapeutic intervention to prevent or delay recurrence. While metastatic breast cancer is considered incurable, molecular analysis of CTCs still have a potential to define particular susceptibilities of the cells representing the current tumor burden, which may differ considerably from the cells of the primary tumor, and offer more tailored therapy to the patients. In this review we inspect the routes to metastasis and how they can be linked to specific features of CTCs, how CTC analysis may be used in therapy, and what is the current status of the research and efforts to include CTC analysis in clinical practice.