Malignant cells facilitate lung metastasis by bringing their own soil. Proc Natl Acad Sci U S A. 2010;107:21677-21682. [PMID: 21098274 DOI: 10.1073/pnas.1016234107]

The Gastrointestinal Tumor Microenvironment: An Updated Biological and Clinical Perspective

Gastrointestinal cancers are still responsible for high numbers of cancer-related deaths despite advances in therapy. Tumor-associated cells play a key role in tumor biology, by supporting or halting tumor development through the production of extracellular matrix, growth factors, cytokines, and extracellular vesicles. Here, we review the roles of these tumor-associated cells in the initiation, angiogenesis, immune modulation, and resistance to therapy of gastrointestinal cancers. We also discuss novel diagnostic and therapeutic strategies directed at tumor-associated cells and their potential benefits for the survival of these patients.

Development of a Stromal Microenvironment Experimental Model Containing Proto-Myofibroblast Like Cells and Analysis of Its Crosstalk with Melanoma Cells: A New Tool to Potentiate and Stabilize Tumor Suppressor Phenotype of Dermal Myofibroblasts

Melanoma is one of the most aggressive solid tumors and includes a stromal microenvironment that regulates cancer growth and progression. The components of stromal microenvironment such as fibroblasts, fibroblast aggregates and cancer-associated fibroblasts (CAFs) can differently influence the melanoma growth during its distinct stages. In this work, we have developed and studied a stromal microenvironment model, represented by fibroblasts, proto-myofibroblasts, myofibroblasts and aggregates of inactivated myofibroblasts, such as spheroids. In particular, we have generated proto-myofibroblasts from primary cutaneous myofibroblasts. The phenotype of proto-myofibroblasts is characterized by a dramatic reduction of α-smooth muscle actin (α-SMA) and cyclooxygenase-2 (COX-2) protein levels, as well as an enhancement of cell viability and migratory capability compared with myofibroblasts. Furthermore, proto-myofibroblasts display the mesenchymal marker vimentin and less developed stress fibers, with respect to myofibroblasts. The analysis of crosstalk between the stromal microenvironment and A375 or A2058 melanoma cells has shown that the conditioned medium of proto-myofibroblasts is cytotoxic, mainly for A2058 cells, and dramatically reduces the migratory capability of both cell lines compared with the melanoma-control conditioned medium. An array analysis of proto-myofibroblast and melanoma cell-conditioned media suggests that lower levels of some cytokines and growth factors in the conditioned medium of proto-myofibroblasts could be associated with their anti-tumor activity. Conversely, the conditioned media of melanoma cells do not influence the cell viability, outgrowth, and migration of proto-myofibroblasts from spheroids. Interestingly, the conditioned medium of proto-myofibroblasts does not alter the cell viability of both BJ-5ta fibroblast cells and myofibroblasts. Hence, proto-myofibroblasts could be useful in the study of new therapeutic strategies targeting melanoma.

CAF Subpopulations: A New Reservoir of Stromal Targets in Pancreatic Cancer

Cancer-associated fibroblasts (CAFs) are one of the most significant components in the tumour microenvironment (TME), where they can perform several protumourigenic functions. Several studies have recently reported that CAFs are more heterogenous and plastic than was previously thought. As such, there has been a shift in the field to study CAF subpopulations and the emergent functions of these subsets in tumourigenesis. In this review, we explore how different aspects of CAF heterogeneity are defined and how these manifest in multiple cancers, with a focus on pancreatic ductal adenocarcinoma (PDAC). We also discuss therapeutic approaches to selectively target protumourigenic CAF functions, while avoiding normal fibroblasts, providing insight into the future of stromal targeting for the treatment of PDAC and other solid tumours.

The Complexities of Metastasis

Therapies that prevent metastatic dissemination and tumor growth in secondary organs are severely lacking. A better understanding of the mechanisms that drive metastasis will lead to improved therapies that increase patient survival. Within a tumor, cancer cells are equipped with different phenotypic and functional capacities that can impact their ability to complete the metastatic cascade. That phenotypic heterogeneity can be derived from a combination of factors, in which the genetic make-up, interaction with the environment, and ability of cells to adapt to evolving microenvironments and mechanical forces play a major role. In this review, we discuss the specific properties of those cancer cell subgroups and the mechanisms that confer or restrict their capacity to metastasize.

Liquid biopsy: one cell at a time

As an alternative target to surgically resected tissue specimens, liquid biopsy has gained much attention over the past decade. Of the various circulating biomarkers, circulating tumor cells (CTCs) have particularly opened new windows into the metastatic cascade, with their functional, biochemical, and biophysical properties. Given the extreme rarity of intact CTCs and the associated technical challenges, however, analyses have been limited to bulk-cell strategies, missing out on clinically significant sources of information from cellular heterogeneity. With recent technological developments, it is now possible to probe genetic material of CTCs at the single-cell resolution to study spatial and temporal dynamics in circulation. Here, we discuss recent transcriptomic profiling efforts that enabled single-cell characterization of patient-derived CTCs spanning diverse cancer types. We further highlight how expression data of these putative biomarkers have advanced our understanding of metastatic spectrum and provided a basis for the development of CTC-based liquid biopsies to track, monitor, and predict the efficacy of therapy and any emergent resistance.

Unravelling tumour heterogeneity by single-cell profiling of circulating tumour cells

Single-cell technologies have contributed to unravelling tumour heterogeneity, now considered a hallmark of cancer and one of the main causes of tumour resistance to cancer therapies. Liquid biopsy (LB), defined as the detection and analysis of cells or cell products released by tumours into the blood, offers an appealing minimally invasive approach that allows the characterization and monitoring of tumour heterogeneity in individual patients. Here, we will review and discuss how circulating tumour cell (CTC) analysis at single-cell resolution provides unique insights into tumour heterogeneity that are not revealed by analysis of circulating tumour DNA (ctDNA) derived from LBs. The molecular analysis of CTCs provides complementary information to that of genomic aberrations determined using ctDNA to fully describe many different cellular components (for example, DNA, RNA, proteins and metabolites) that can influence tumour heterogeneity.

Cell Heterogeneity and Phenotypic Plasticity in Metastasis Formation: The Case of Colon Cancer

The adenoma-to-carcinoma progression in colon cancer is driven by a sequential accumulation of genetic alterations at specific tumor suppressors and oncogenes. In contrast, the multistage route from the primary site to metastasis formation is underlined by phenotypic plasticity, i.e., the capacity of disseminated tumor cells to undergo transiently and reversible transformations in order to adapt to the ever-changing environmental contexts. Notwithstanding the considerable body of evidence in support of the role played by epithelial-to-mesenchymal transition (EMT)/mesenchymal-to-epithelial transition (MET) in metastasis, its rate-limiting function, the detailed underlying cellular and molecular mechanisms, and the extension of the necessary morphologic and epigenetic changes are still a matter of debate. Rather than leading to a complete epithelial or mesenchymal state, the EMT/MET-program generates migrating cancer cells displaying intermediate phenotypes featuring both epithelial and mesenchymal characteristics. In this review, we will address the role of colon cancer heterogeneity and phenotypic plasticity in metastasis formation and the contribution of EMT to these processes. The alleged role of hybrid epithelial/mesenchymal (E/M) in collective and/or single-cell migration during local dissemination at the primary site and more systemic spreading will also be highlighted.

Circulating tumor cells exit circulation while maintaining multicellularity, augmenting metastatic potential

Metastasis accounts for the majority of all cancer deaths, yet the process remains poorly understood. A pivotal step in the metastasis process is the exiting of tumor cells from the circulation, a process known as extravasation. However, it is unclear how tumor cells extravasate and whether multicellular clusters of tumor cells possess the ability to exit as a whole or must first disassociate. In this study, we use in vivo zebrafish and mouse models to elucidate the mechanism tumor cells use to extravasate. We found that circulating tumor cells exit the circulation using the recently identified extravasation mechanism, angiopellosis, and do so as both clusters and individual cells. We further show that when melanoma and cervical cancer cells utilize this extravasation method to exit as clusters, they exhibit an increased ability to form tumors at distant sites through the expression of unique genetic profiles. Collectively, we present a new model for tumor cell extravasation of both individual and multicellular circulating tumor cells.This article has an associated First Person interview with the first author of the paper.

Cancer Stem Cells and Targeting Strategies

Chemoresistance is a major problem in cancer therapy as cancer cells develop mechanisms that counteract the effect of chemotherapeutic compounds, leading to relapse and the development of more aggressive cancers that contribute to poor prognosis and survival rates of treated patients. Cancer stem cells (CSCs) play a key role in this event. Apart from their slow proliferative property, CSCs have developed a range of cellular processes that involve drug efflux, drug enzymatic inactivation and other mechanisms. In addition, the microenvironment where CSCs evolve (CSC niche), effectively contributes to their role in cancer initiation, progression and chemoresistance. In the CSC niche, immune cells, mesenchymal stem cells (MSCs), endothelial cells and cancer associated fibroblasts (CAFs) contribute to the maintenance of CSC malignancy via the secretion of factors that promote cancer progression and resistance to chemotherapy. Due to these factors that hinder successful cancer therapies, CSCs are a subject of intense research that aims at better understanding of CSC behaviour and at developing efficient targeting therapies. In this review, we provide an overview of cancer stem cells, their role in cancer initiation, progression and chemoresistance, and discuss the progress that has been made in the development of CSC targeted therapies.

Biomechanical Microenvironment Regulates Fusogenicity of Breast Cancer Cells

Fusion of cancer cells is thought to contribute to tumor development and drug resistance. The low frequency of cell fusion events and the instability of fused cells have hindered our ability to understand the molecular mechanisms that govern cell fusion. We have demonstrated that several breast cancer cell lines can fuse into multinucleated giant cells in vitro, and the initiation and longevity of fused cells can be regulated solely by biophysical factors. Dynamically tuning the adhesive area of the patterned substrates, reducing cytoskeletal tensions pharmacologically, altering matrix stiffness, and modulating pattern curvature all supported the spontaneous fusion and stability of these multinucleated giant cells. These observations highlight that the biomechanical microenvironment of cancer cells, including the matrix rigidity and interfacial curvature, can directly modulate their fusogenicity, an unexplored mechanism through which biophysical cues regulate tumor progression.

Cancer-associated fibroblasts in desmoplastic tumors: emerging role of integrins

The tumor microenvironment (TME) is a complex meshwork of extracellular matrix (ECM) macromolecules filled with a collection of cells including cancer-associated fibroblasts (CAFs), blood vessel associated smooth muscle cells, pericytes, endothelial cells, mesenchymal stem cells and a variety of immune cells. In tumors the homeostasis governing ECM synthesis and turnover is disturbed resulting in abnormal blood vessel formation and excessive fibrillar collagen accumulations of varying stiffness and organization. The disturbed ECM homeostasis opens up for new types of paracrine, cell-cell and cell-ECM interactions with large consequences for tumor growth, angiogenesis, metastasis, immune suppression and resistance to treatments. As a main producer of ECM and paracrine signals the CAF is a central cell type in these events. Whereas the paracrine signaling has been extensively studied in the context of tumor-stroma interactions, the nature of the numerous integrin-mediated cell-ECM interactions occurring in the TME remains understudied. In this review we will discuss and dissect the role of known and potential CAF interactions in the TME, during both tumorigenesis and chemoresistance-induced events, with a special focus on the "interaction landscape" in desmoplastic breast, lung and pancreatic cancers. As an example of the multifaceted mode of action of the stromal collagen receptor integrin α11β1, we will summarize our current understanding on the role of this CAF-expressed integrin in these three tumor types.

Fluorescence monitoring of rare circulating tumor cell and cluster dissemination in a multiple myeloma xenograft model in vivo

Circulating tumor cells (CTCs) are of great interest in cancer research because of their crucial role in hematogenous metastasis. We recently developed “diffuse in vivo flow cytometry” (DiFC), a preclinical research tool for enumerating extremely rare fluorescently labeled CTCs directly in vivo. In this work, we developed a green fluorescent protein (GFP)-compatible version of DiFC and used it to noninvasively monitor tumor cell numbers in circulation in a multiple myeloma (MM) disseminated xenograft mouse model. We show that DiFC allowed enumeration of CTCs in individual mice overtime during MM growth, with sensitivity below 1  CTC mL  −  1 of peripheral blood. DiFC also revealed the presence of CTC clusters (CTCCs) in circulation to our knowledge for the first time in this model and allowed us to calculate CTCC size, frequency, and kinetics of shedding. We anticipate that the unique capabilities of DiFC will have many uses in preclinical study of metastasis, in particular, with a large number of GFP-expressing xenograft and transgenic mouse models.

Targeting the Interplay Between Cancer Fibroblasts, Mesenchymal Stem Cells, and Cancer Stem Cells in Desmoplastic Cancers

Malignant tumors are highly heterogeneous and likely contain a subset of cancer cells termed cancer stem cells (CSCs). CSCs exist in a dynamic equilibrium with their microenvironments and the CSC phenotype is tightly regulated by both cell-intrinsic and cell-extrinsic factors including those derived from their surrounding cells or stroma. Many human solid tumors like breast, lung, colorectal and pancreatic cancers are characterized by a pronounced stromal reaction termed “the desmoplastic response.” Carcinoma-associated fibroblasts (CAFs) derived either from resident fibroblasts or tumor-infiltrating mesenchymal stem cells (MSCs) are a major component of the stroma in desmoplastic cancers. Recent studies identified subpopulations of CAFs proficient in secreting a plethora of factors to foster CSCs, tumor growth, and invasion. In addition, cytotoxic therapy can lead to the enrichment of functionally perturbed CAFs, which are endowed with additional capabilities to enhance cancer stemness, leading to treatment resistance and tumor aggressiveness. When recruited into the tumor stroma, bone-marrow-derived MSCs can promote cancer stemness by secreting a specific set of paracrine factors or converting into pro-stemness CAFs. Thus, blockade of the crosstalk of pro-stemness CAFs and MSCs with CSCs may provide a new avenue to improving the therapeutic outcome of desmoplastic tumors. This up-to-date, in-depth and balanced review describes the recent progress in understanding the pro-stemness roles of CAFs and tumor-infiltrating MSCs and the associated paracrine signaling processes. We emphasize the effects of systemic chemotherapy on the CAF/MSC–CSC interplay. We summarize various promising and novel approaches in mitigating the stimulatory effect of CAFs or MSCs on CSCs that have shown efficacies in preclinical models of desmoplastic tumors and highlight the unique advantages of CAF- or MSC-targeted therapies. We also discuss potential challenges in the clinical development of CSC- or MSC-targeted therapies and propose CAF-related biomarkers that can guide the next-generation clinical studies.

Circulating Tumor Cell Clusters in Patients with Metastatic Breast Cancer: a SWOG S0500 Translational Medicine Study

PURPOSE

Metastasis requires malignant cell circulation from the primary to a distant tissue. Elevated levels of circulating tumor cells (CTC) portend a poor prognosis in breast and other cancers. Recent studies have suggested that CTC clusters may be a factor in the metastatic process. We conducted a prospective retrospective study of the SWOG0500 clinical trial to test whether CTC clusters are associated with poorer prognosis.

EXPERIMENTAL DESIGN

CTC CellSearch galleries from SWOG0500 trial were reread using prespecified criteria for CTC clusters, doublets, and enumeration. Survival analysis methods include Kaplan-Meier plots and log-rank tests.

RESULTS

Patients were classified into three prognostic subgroups based on baseline CTC/7.5 mL whole blood (WB): Arm A: <5CTC; Arm B/C: ≥5CTC and then B (<5CTC) and C (≥5CTC)/7.5 mL WB at first follow-up. At baseline, 19% of patients had CTC doublets or clusters, which were more likely in Arm B/C versus Arm A (38% vs. 1.4%; P < 0.0001). Furthermore, doublets or clusters were significantly more common in patients who were ultimately assigned to Arm C versus B (54% vs. 25%; P < 0.0001). In Arm C, doublets and clusters were associated with worse overall survival than only doublets, clusters, or no doublets nor clusters at baseline (P = 0.008) and first follow-up (P = 0.010). When compared with enumeration alone, doublets, clusters, or both were not prognostic in patients who had 5-19 or ≥20 CTC/7.5 mL WB.

CONCLUSIONS

In patients with metastatic breast cancer starting first-line chemotherapy, mortality is independent of the presence of CTC clusters, but rather depends on the number of CTC/7.5 mL WB.

Cancer-associated fibroblasts-heroes or villains?

Cancer-associated fibroblasts (CAFs) were originally presumed to represent a homogeneous population uniformly driving tumorigenesis, united by their morphology and peritumoural location. Our understanding of CAFs has since been shaped by sophisticated in vitro and in vivo experiments, pathological association and, more recently, ablation, and it is now widely appreciated that CAFs form a group of highly heterogeneous cells with no single overarching marker. Studies have demonstrated that the CAF population contains different subtypes based on the expression of marker proteins with the capacity to promote or inhibit cancer, with their biological role as accomplices or adversaries dependent on many factors, including the cancer stage. So, while CAFs have been endlessly shown to promote the growth, survival and spread of tumours via improvements in functionality and an altered secretome, they are also capable of retarding tumorigenesis via largely unknown mechanisms. It is important to reconcile these disparate results so that the functions of, or factors produced by, tumour-promoting subtypes can be specifically targeted to improve cancer patient outcomes. This review will dissect out CAF complexity and CAF-directed cancer treatment strategies in order to provide a case for future, rational therapies.

Tenascin-C increases lung metastasis by impacting blood vessel invasions

Metastasis is a major cause of death in cancer patients. The extracellular matrix molecule tenascin-C is a known promoter of metastasis, however the underlying mechanisms are not well understood. To further analyze the impact of tenascin-C on cancer progression we generated MMTV-NeuNT mice that develop spontaneous mammary tumors, on a tenascin-C knockout background. We also developed a syngeneic orthotopic model in which tumor cells derived from a MMTV-NeuNT tumor. Tumor cells were transfected with control shRNA or with shRNA to knockdown tenascin-C expression and, were grafted into the mammary gland of immune competent, wildtype or tenascin-C knockout mice. We show that stromal-derived tenascin-C increases metastasis by reducing apoptosis and inducing the cellular plasticity of cancer cells located in pulmonary blood vessels invasions (BVI), before extravasation. We characterized BVI as organized structures of tightly packed aggregates of proliferating tumor cells with epithelial characteristics, surrounded by Fsp1+ cells, internally located platelets and, a luminal monolayer of endothelial cells. We found extracellular matrix, in particular, tenascin-C, between the stromal cells and the tumor cell cluster. In mice lacking stromal-derived tenascin-C, the organization of pulmonary BVI was significantly affected, revealing novel functions of host-derived tenascin-C in supporting the integrity of the endothelial cell coat, increasing platelet abundance, tumor cell survival, epithelial plasticity, thereby promoting overall lung metastasis. Many effects of tenascin-C observed in BVI including enhancement of cellular plasticity, survival and migration, could be explained by activation of TGF-β signaling. Finally, in several human cancers, we also observed BVI to be surrounded by an endothelial monolayer and to express tenascin-C. Expression of tenascin-C is specific to BVI and is not observed in lymphatic vascular invasions frequent in breast cancer, which lack an endothelial lining. Given that BVI have prognostic significance for many tumor types, such as shorter cancer patient survival, increased metastasis, vessel occlusion, and organ failure, our data revealing a novel mechanism by which stromal tenascin-C promotes metastasis in human cancer, may have potential for diagnosis and therapy.

Limiting tumor seeding as a therapeutic approach for metastatic disease

Here we propose that therapeutic targeting of circulating tumor cells (CTCs), which are widely understood to be the seeds of metastasis, would represent an effective strategy towards limiting numerical expansion of secondary lesions and containing overall tumor burden in cancer patients. However, the molecular mediators of tumor seeding have not been well characterized. This is in part due to the limited number of pre-clinical in vivo approaches that appropriately interrogate the mechanisms by which cancer cells home to arresting organs. It is critical that we continue to investigate the mediators of tumor seeding as it is evident that the ability of CTCs to colonize in distant sites is what drives disease progression even after the primary tumor has been ablated by local modalities. In addition to slowing disease progression, containing metastatic spread by impeding tumor cell seeding may also provide a clinical benefit by increasing the duration of the residence of CTCs in systemic circulation thereby increasing their exposure to pharmacological agents commonly used in the treatment of patients such as chemotherapy and immunotherapies. In this review we will examine the current state of knowledge about the mechanisms of tumor cells seeding as well as explore how targeting this stage of metastatic spreading may provide therapeutic benefit to patients with advanced disease.

A microfluidic device for label-free isolation of tumor cell clusters from unprocessed blood samples

Primary cancers disseminate both single circulating tumor cells (CTCs) and CTC "clusters," the latter of which have been shown to demonstrate greater metastatic propensity and adverse impact on prognosis. Many devices developed to isolate single CTCs also capture CTC clusters, but there is translational potential for a platform specifically designed to isolate CTC clusters. Herein, we introduce our microfluidic device for isolating CTC clusters ("Microfluidic Isolation of CTC Clusters" or MICC), which is equipped with ∼10 000 trap chambers that isolate tumor cell clusters based on their large sizes and dynamic force balance against a pillar obstacle in the trap chamber. Whole blood is injected, followed by a wash step to remove blood cells and a final backflush to release intact clusters for downstream analysis. Using clusters from tumor cell-line and confocal microscopy, we verified the ability of the MICC platform to specifically capture tumor cell clusters in the trap chambers. Our flow rate optimization experiments identified 25 μl/min for blood injection, 100 μl/min as wash flow rate, and 300 μl/min as the release flow rate - indicating that 1 ml of whole blood can be processed in less than an hour. Under these optimal flow conditions, we assessed the MICC platform's capture and release performance using blood samples spiked with different concentrations of clusters, revealing a capture efficiency of 66%-87% and release efficiency of 76%-90%. The results from our study suggest that the MICC platform has the potential to isolate CTC clusters from cancer patient blood, enabling it for clinical applications in cancer management.

Stromal-induced mitochondrial re-education: Impact on epithelial-to-mesenchymal transition and cancer aggressiveness

Metabolic reprogramming as well as the flexible utilisation of fuel sources by tumour cells has been considered not only intrinsic to malignant cells but also sustained by resident and/or recruited stromal cells. The complexity of tumour-stroma cross-talk is experienced by neoplastic cells through profound changes in the own metabolic machinery. In such context, mitochondria are dynamic organelles that receive, orchestrate and exchange a multiplicity of stromal cues within the tumour cells to finely regulate key metabolic and signalling pathways, allowing malignant cells to adapt and thrive in an ever-changing environment. In this review, we focus on how tumour mitochondria are coached by stromal metabolic supply and how this re-education sustains tumour malignant traits.

Protein Glycosylation and Tumor Microenvironment Alterations Driving Cancer Hallmarks

Decades of research have disclosed a plethora of alterations in protein glycosylation that decisively impact in all stages of disease and ultimately contribute to more aggressive cell phenotypes. The biosynthesis of cancer-associated glycans and its reflection in the glycoproteome is driven by microenvironmental cues and these events act synergistically toward disease evolution. Such intricate crosstalk provides the molecular foundations for the activation of relevant oncogenic pathways and leads to functional alterations driving invasion and disease dissemination. However, it also provides an important source of relevant glyco(neo)epitopes holding tremendous potential for clinical intervention. Therefore, we highlight the transversal nature of glycans throughout the currently accepted cancer hallmarks, with emphasis on the crosstalk between glycans and the tumor microenvironment stromal components. Focus is also set on the pressing need to include glycans and glycoconjugates in comprehensive panomics models envisaging molecular-based precision medicine capable of improving patient care. We foresee that this may provide the necessary rationale for more comprehensive studies and molecular-based intervention.

Prognostic significance of histological categorization of desmoplastic reaction in colorectal liver metastases

Desmoplastic reaction (DR) involves the growth of fibrous or connective tissues around a tumor and has recently attracted attention as an indicator of malignant potential. Previous studies have confirmed that histological categorization of DR in the primary tumor is an independent prognostic factor in patients with colorectal liver metastases (CRLM). However, it remains unclear whether the DR status of the metastatic liver lesion (DR^liver) is a useful prognostic factor. This pathological review evaluated records from 204 patients who underwent hepatectomy for CRLM at the National Defense Medical College Hospital in Japan. Each case's DR^liver was classified as mature, intermediate, or immature based on the presence of keloid-like collagen and myxoid stroma in the metastatic liver lesion. This resulted in 12 cases of mature DR^liver, 101 cases of intermediate DR^liver, and 91 cases of immature DR^liver. There was a significant correlation between the DR statuses of the primary tumor and the metastatic liver lesion (Spearman's rho = 0.3, P = 0.0001). The 5-year relapse-free survival rates after hepatectomy were 33.8% for mature/intermediate DR^liver and 16.7% for immature DR^liver (P = 0.0021). The 5-year overall survival rate after hepatectomy was higher in the mature/intermediate DR^liver group (64.8%) than in the immature DR^liver group (35.0%; P = 0.0012). The multivariate analysis confirmed that DR^liver categorization could independently predict relapse-free survival and overall survival. In conclusion, DR^liver categorization may be valuable for predicting prognosis after hepatectomy among patients with CRLM.

Mesenchymal Stem Cells, Immune Cells and Tumor Cells Crosstalk: A Sinister Triangle in the Tumor Microenvironment

Mesenchymal Stem Cells [MSCs] are a heterogeneous population of fibroblast-like cells which maintain self-renewability and pluripotency. Many studies have demonstrated the immunomodulatory effects of MSCs on the innate and adaptive immune cells. As a result of interactions with tumor cells, microenvironment and immune-stimulating milieu, MSCs contribute to tumor progression by several mechanisms, including sustained proliferative signal in cancer stem cells [CSCs], inhibition of tumor cell apoptosis, transition to tumor-associated fibroblasts [TAFs], promotion of angiogenesis, stimulation of epithelial-mesenchymal transition [EMT], suppression of immune responses, and consequential promotion of tumor metastasis. Here, we present an overview of the latest findings on Janusfaced roles that MSCs play in the tumor microenvironment [TME], with a concise focus on innate and adaptive immune responses.

Development of a Cross-Reactive Monoclonal Antibody for Detecting the Tumor Stroma

Here, we document the discovery of a monoclonal antibody that selectively binds to both human and murine fibroblast activation protein alpha (FAP), a serine protease that is overexpressed on cancer-associated fibroblasts (CAFs), making it an attractive therapeutic target for the aiding and abetting tumor microenvironment. The lead antibody, B12, was identified from a naïve murine single-chain variable fragment antibody phage display library screened against recombinant human FAP on magnetic beads. The heavy and light chains of B12 were cloned into full-length human immunoglobulin 1 (IgG) vectors and expressed as a chimeric monoclonal antibody (B12 IgG). We engineered a drug-resistant prostate cancer cell line, CWR-R1-EnzR, to express human FAP for antibody characterization and validation (R1-EnzR^FAP). B12 IgG selectively bound to the R1-EnzR^FAP cells by flow cytometry and was internalized in vitro by confocal microscopy. B12 IgG was further evaluated as a near-infrared (NIR) optical imaging probe in R1-EnzR^FAP and parental xenograft models. High tumor uptake and retention of the NIR probe was observed in the R1-EnzR^FAP xenografts, and endogenous expression of murine stromal origin FAP was detected in the parental xenografts. Ex vivo evaluation of these models by immunohistochemistry documented B12 IgG localization to both human and murine FAP-expressing cells.

Host tissue determinants of tumour immunity

Although common evolutionary principles drive the growth of cancer cells regardless of the tissue of origin, the microenvironment in which tumours arise substantially differs across various organ sites. Recent studies have established that, in addition to cell-intrinsic effects, tumour growth regulation also depends on local cues driven by tissue environmental factors. In this Review, we discuss how tissue-specific determinants might influence tumour development and argue that unravelling the tissue-specific contribution to tumour immunity should help the development of precise immunotherapeutic strategies for patients with cancer.

Energetic regulation of coordinated leader-follower dynamics during collective invasion of breast cancer cells

The ability of primary tumor cells to invade into adjacent tissues, followed by the formation of local or distant metastasis, is a lethal hallmark of cancer. Recently, locomoting clusters of tumor cells have been identified in numerous cancers and associated with increased invasiveness and metastatic potential. However, how the collective behaviors of cancer cells are coordinated and their contribution to cancer invasion remain unclear. Here we show that collective invasion of breast cancer cells is regulated by the energetic statuses of leader and follower cells. Using a combination of in vitro spheroid and ex vivo organoid invasion models, we found that cancer cells dynamically rearrange leader and follower positions during collective invasion. Cancer cells invade cooperatively in denser collagen matrices by accelerating leader-follower switching thus decreasing leader cell lifetime. Leader cells exhibit higher glucose uptake than follower cells. Moreover, their energy levels, as revealed by the intracellular ATP/ADP ratio, must exceed a threshold to invade. Forward invasion of the leader cell gradually depletes its available energy, eventually leading to leader-follower transition. Our computational model based on intracellular energy homeostasis successfully recapitulated the dependence of leader cell lifetime on collagen density. Experiments further supported model predictions that decreasing the cellular energy level by glucose starvation decreases leader cell lifetime whereas increasing the cellular energy level by AMP-activated kinase (AMPK) activation does the opposite. These findings highlight coordinated invasion and its metabolic regulation as potential therapeutic targets of cancer.

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

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

Metastases in Prostate Cancer

Prostate cancer (PCa) prognosis and clinical outcome is directly dependent on metastatic occurrence. The bone microenvironment is a favorable metastatic niche. Different biological processes have been suggested to contribute to the osteotropism of PCa such as hemodynamics, bone-specific signaling interactions, and the "seed and soil" hypothesis. However, prevalence of disseminating tumor cells in the bone is not proportional to the actual occurrence of metastases, as not all patients will develop bone metastases. The fate and tumor-reforming ability of a metastatic cell is greatly influenced by the microenvironment. In this review, the molecular mechanisms of bone and soft-tissue metastasis in PCa are discussed. Specific attention is dedicated to the residual disease, novel approaches, and animal models used in oncological translational research are illustrated.

Heterotypic CAF-tumor spheroids promote early peritoneal metastatis of ovarian cancer

The study provides insights in HGSOC by identifying that ascitic CAFs selectively recruit ITGA5^high ascitic tumor cells to form heterotypic spheroids named metastatic units (MUs), which actively engage in peritoneal metastasis, discriminates HGSOC from LGSOC, and act as therapeutic targets in hampering OC metastasis.

High-grade serous ovarian cancer (HGSOC) is hallmarked by early onset of peritoneal dissemination, which distinguishes it from low-grade serous ovarian cancer (LGSOC). Here, we describe the aggressive nature of HGSOC ascitic tumor cells (ATCs) characterized by integrin α5^high (ITGA5^high) ATCs, which are prone to forming heterotypic spheroids with fibroblasts. We term these aggregates as metastatic units (MUs) in HGSOC for their advantageous metastatic capacity and active involvement in early peritoneal dissemination. Intriguingly, fibroblasts inside MUs support ATC survival and guide their peritoneal invasion before becoming essential components of the tumor stroma in newly formed metastases. Cancer-associated fibroblasts (CAFs) recruit ITGA5^high ATCs to form MUs, which further sustain ATC ITGA5 expression by EGF secretion. Notably, LGSOC is largely devoid of CAFs and the resultant MUs, which might explain its metastatic delay. These findings identify a specialized MU architecture that amplifies the tumor–stroma interaction and promotes transcoelomic metastasis in HGSOC, providing the basis for stromal fibroblast-oriented interventions in hampering OC peritoneal propagation.

Blocking CXCR4 alleviates desmoplasia, increases T-lymphocyte infiltration, and improves immunotherapy in metastatic breast cancer

Metastatic breast cancers (mBCs) are largely resistant to immune checkpoint blockade, but the mechanisms remain unclear. Primary breast cancers are characterized by a dense fibrotic stroma, which is considered immunosuppressive in multiple malignancies, but the stromal composition of breast cancer metastases and its role in immunosuppression are largely unknown. Here we show that liver and lung metastases of human breast cancers tend to be highly fibrotic, and unlike primary breast tumors, they exclude cytotoxic T lymphocytes (CTLs). Unbiased analysis of the The Cancer Genome Atlas database of human breast tumors revealed a set of genes that are associated with stromal T-lymphocyte exclusion. Among these, we focused on CXCL12 as a relevant target based on its known roles in immunosuppression in other cancer types. We found that the CXCL12 receptor CXCR4 is highly expressed in both human primary tumors and metastases. To gain insight into the role of the CXCL12/CXCR4 axis, we inhibited CXCR4 signaling pharmacologically and found that plerixafor decreases fibrosis, alleviates solid stress, decompresses blood vessels, increases CTL infiltration, and decreases immunosuppression in murine mBC models. By deleting CXCR4 in αSMA⁺ cells, we confirmed that these immunosuppressive effects are dependent on CXCR4 signaling in αSMA⁺ cells, which include cancer-associated fibroblasts as well as other cells such as pericytes. Accordingly, CXCR4 inhibition more than doubles the response to immune checkpoint blockers in mice bearing mBCs. These findings demonstrate that CXCL12/CXCR4-mediated desmoplasia in mBC promotes immunosuppression and is a potential target for overcoming therapeutic resistance to immune checkpoint blockade in mBC patients.

Integrative diagnosis of cancer by combining CTCs and associated peripheral blood cells in liquid biopsy

Circulating tumor cells (CTCs), as cells shed from solid tumor into the vasculature, play a significant role in tumor metastasis. In the peripheral blood, immune cells and stromal cells can interact with CTCs and influence their biological behaviors of survival, proliferation, dissemination, and immune evasion. These peripheral blood cells can evolve synergistically with CTCs to constitute the liquid microenvironment which is essential for tumor progression. Here, we review the mechanisms of peripheral blood cells interacting with CTCs and uncover their effects on both CTCs and tumor metastasis. Then, we introduce the applications of these CTC-associated peripheral blood cells in the clinical setting. Besides, some peripheral blood cell subsets are of additional clinical values to CTCs in cancer diagnosis and prognosis. To improve the clinical utility of CTCs, an integrative analysis of CTCs and associated peripheral blood cells should be advocated for, which could provide a novel insight into tumor biology and offer comprehensive information in cancer diagnosis, prognosis, and therapy efficacy evaluation.

Circulating tumor cells as "liquid biopsies" to understand cancer metastasis

Circulating tumor cells (CTCs) are a subset of cancer cells that are shed from the primary or metastatic tumors into the bloodstream. CTCs are responsible for the establishment of blood-borne distant metastases but their rarity, estimated at one CTC per billion blood cells, presents the biggest technical barrier to their functional studies. Recent advances in CTC isolation technology have allowed for the reliable capture of CTCs from the whole blood of cancer patients. The ability to derive clinically relevant information from CTCs isolated through a blood draw allows for the monitoring of active disease, avoiding the invasiveness inherent to traditional biopsy techniques. This review will summarize recent developments in CTC isolation technology; the development of CTC-derived models; the unique molecular characteristics of CTCs at the transcriptomic, genomic, and proteomic levels; and how these characteristics have been correlated to prognosis and therapeutic efficacy. Finally, we will summarize the recent findings on several signaling pathways in CTCs and metastasis. The study of CTCs is central to understanding cancer biology and promises a "liquid biopsy" that can monitor disease status and guide therapeutic management in real time.

Characterizing Circulating Tumor Cells Isolated from Metastatic Breast Cancer Patients Using Graphene Oxide Based Microfluidic Assay

The enumeration of circulating tumor cells (CTCs) has shown prognostic importance in patients with breast cancer. However, CTCs are highly heterogeneous with diverse functional properties, which may also be clinically relevant. To provide a comprehensive landscape of the patient's disease, further CTC analysis is required. Here, a highly sensitive and reproducible graphene oxide based CTC assay is utilized to isolate and characterize CTCs from 47 metastatic breast cancer patients. The CTCs are captured with high purity, requiring only a few milliliters of blood and enabling efficient enumeration and subsequent analysis at both the protein and the transcription level. The results show that patient clinical outcomes correlate with the associated CTC profile and clearly demonstrate the potential use of the assay in the clinical setting. Collectively, these findings suggest that beyond simple enumeration, CTC characterization may provide further information that improves the diagnosis of the patients' disease status for proper treatment decisions. Moreover, this thorough validation study will facilitate the translation of the CTC assay into future clinical applications to broaden the utility of liquid biopsy.

Molecular mechanisms of IL-33-mediated stromal interactions in cancer metastasis

Molecular mechanisms underlying the cancer stroma in metastasis need further exploration. Here, we discovered that cancer-associated fibroblasts (CAFs) produced high levels of IL-33 that acted on tumor-associated macrophages (TAMs), causing them to undergo the M1 to M2 transition. Genomic profiling of metastasis-related genes in the IL-33-stimulated TAMs showed a >200-fold increase of MMP9. Signaling analysis demonstrated the IL-33-ST2-NF-κB-MMP9-laminin pathway that governed tumor stroma-mediated metastasis. In mouse and human fibroblast-rich pancreatic cancers, genetic deletion of IL-33, ST2, or MMP9 markedly blocked metastasis. Pharmacological inhibition of NF-κB and MMP9 also blocked cancer metastasis. Deletion of IL-33, ST2, or MMP9 restored laminin, a key basement membrane component associated with tumor microvessels. Together, our data provide mechanistic insights on the IL-33-NF-κB-MMP9-laminin axis that mediates the CAF-TAM-committed cancer metastasis. Thus, targeting the CAF-TAM-vessel axis provides an outstanding therapeutic opportunity for cancer treatment.

The impact of cancer-associated fibroblasts on major hallmarks of pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) constitutes one of the most challenging lethal tumors and has a very poor prognosis. In addition to cancer cells, the tumor microenvironment created by a repertoire of resident and recruited cells and the extracellular matrix also contribute to the acquisition of hallmarks of cancer. Among these factors, cancer-associated fibroblasts (CAFs) are critical components of the tumor microenvironment. CAFs originate from the activation of resident fibroblasts and pancreatic stellate cells, the differentiation of bone marrow-derived mesenchymal stem cells and epithelial-to-mesenchymal transition. CAFs acquire an activated phenotype via various cytokines and promote tumor proliferation and growth, accelerate invasion and metastasis, induce angiogenesis, promote inflammation and immune destruction, regulate tumor metabolism, and induce chemoresistance; these factors contribute to the acquisition of major hallmarks of PDAC. Therefore, an improved understanding of the impact of CAFs on the major hallmarks of PDAC will highlight the diagnostic and therapeutic values of these targeted cells.

Tumor⁻Stroma Cross-Talk in Human Pancreatic Ductal Adenocarcinoma: A Focus on the Effect of the Extracellular Matrix on Tumor Cell Phenotype and Invasive Potential

The extracellular matrix (ECM) in the tumor microenvironment modulates the cancer cell phenotype, especially in pancreatic ductal adenocarcinoma (PDAC), a tumor characterized by an intense desmoplastic reaction. Because the epithelial-to-mesenchymal transition (EMT), a process that provides cancer cells with a metastatic phenotype, plays an important role in PDAC progression, the authors aimed to explore in vitro the interactions between human PDAC cells and ECM components of the PDAC microenvironment, focusing on the expression of EMT markers and matrix metalloproteinases (MMPs) that are able to digest the basement membrane during tumor invasion. EMT markers and the invasive potential of HPAF-II, HPAC, and PL45 cells grown on different ECM substrates (fibronectin, laminin, and collagen) were analyzed. While N-cadherin, αSMA, and type I collagen were not significantly affected by ECM components, the E-cadherin/β-catenin complex was highly expressed in all the experimental conditions, and E-cadherin was upregulated by collagen in PL45 cells. Cell migration was unaffected by fibronectin and delayed by laminin. In contrast, collagen significantly stimulated cell migration and the secretion of MMPs. This study's results showed that ECM components impacted cell migration and invasive potential differently. Collagen exerted a more evident effect, providing new insights into the understanding of the intricate interplay between ECM molecules and cancer cells, in order to find novel therapeutic targets for PDAC treatment.

The evolving relationship of wound healing and tumor stroma

The stroma in solid tumors contains a variety of cellular phenotypes and signaling pathways associated with wound healing, leading to the concept that a tumor behaves as a wound that does not heal. Similarities between tumors and healing wounds include fibroblast recruitment and activation, extracellular matrix (ECM) component deposition, infiltration of immune cells, neovascularization, and cellular lineage plasticity. However, unlike a wound that heals, the edges of a tumor are constantly expanding. Cell migration occurs both inward and outward as the tumor proliferates and invades adjacent tissues, often disregarding organ boundaries. The focus of our review is cancer associated fibroblast (CAF) cellular heterogeneity and plasticity and the acellular matrix components that accompany these cells. We explore how similarities and differences between healing wounds and tumor stroma continue to evolve as research progresses, shedding light on possible therapeutic targets that can result in innovative stromal-based treatments for cancer.

Brcal Defective Breast Cancer Cells Induce in vitro Transformation of Cancer Associated Fibroblasts (CAFs) to Metastasis Associated Fibroblasts (MAF)

It is known that Cancer Associated Fibroblast (CAFs) from the primary tumor site can accompany cancer cells to a secondary site during the process of metastasis. We hypothesize that these CAFs could be transformed to an altered cell type, which can be called as Metastasis Associated Fibroblasts (MAF) in turn can support, and convoy cancer cells for metastasis. There are no published reports that have characterized and distinguished CAFs from MAF. It is well established that some of the cancer cells within the tumor mass accumulate novel mutations prior to metastasis. Hence, we speculated that mutations in the tumor suppressor gene, BRCA1, which is already reported to induce metastasis via abnormal expression of Ezrin, Radixin and Moesin (ERM), could generate MAF. In the present study, we demonstrate for the first time that CAFs isolated from primary breast cancer tissues when co-cultured with BRCA1 mutated HCC1937 cells transform CAFs to MAF in vitro. As expected, MAF augmented proliferation, migration and invasion along with over-expression of epithelial mesenchymal transition (EMT) markers, Ezrin and CCL5, thereby facilitating metastasis. Therefore, we inhibited Ezrin and CCL5 in vitro in MAF and observed that the migration and invasion abilities of these cells were attenuated. This highlights the intriguing possibilities of combination therapy using MAF inhibitors as anti-metastatic agents along with anticancer drugs, to control the metastatic spread from primary tumor site.

The Interplay between Circulating Tumor Cells and the Immune System: From Immune Escape to Cancer Immunotherapy

Circulating tumor cells (CTCs) have aroused increasing interest not only in mechanistic studies of metastasis, but also for translational applications, such as patient monitoring, treatment choice, and treatment change due to tumor resistance. In this review, we will assess the state of the art about the study of the interactions between CTCs and the immune system. We intend to analyze the impact that the cells of the immune system have in limiting or promoting the metastatic capability of CTCs. To this purpose, we will examine studies that correlate CTCs, immune cells, and patient prognosis, and we will also discuss relevant animal models that have contributed to the understanding of the mechanisms of immune-mediated metastasis. We will then consider some studies in which CTCs seem to play a promising role in monitoring cancer patients during immunotherapy regimens. We believe that, from an accurate and profound knowledge of the interactions between CTCs and the immune system, new immunotherapeutic strategies against cancer might emerge in the future.

Immunohistochemical characterization of cancer-associated fibroblasts at the primary sites and in the metastatic lymph nodes of human intrahepatic cholangiocarcinoma

Cancer-associated fibroblasts (CAFs) are an important constituent of the cancer stroma. In intrahepatic cholangiocarcinoma (ICC), the features of CAFs at the primary site and in the metastatic lymph nodes (Met-LNs) and their origin have been unclear. In the present study, we characterized CAFs at the primary site (n = 42) and in the Met-LNs (n = 10) of human ICC by immunohistochemistry using potential molecular markers of CAFs, portal fibroblasts (PFs), hepatic stellate cells (HSCs), and bone marrow-derived fibrocytes (BMDFs). At the primary site, the stroma was strongly positive for α-smooth muscle actin (α-SMA; marker for CAFs), platelet-derived growth factor receptor-β (PDGFR-β) (common marker for HSCs and PFs), fibulin-2, and thymus cell antigen-1 (Thy-1; PF marker), whereas immunoreactivity for fascin (HSC marker) was scarce. Most of the α-SMA-positive cells were found to express PDGFR-β, Thy-1, and fibulin-2 by double immunostaining. A small population of BMDF marker-positive (α-SMA⁺CD45⁺CD34⁺) cells was found by triple immunostaining. In the micro-Met-LNs, α-SMA-positive cells were absent in cancer aggregates of the LN sinus, whereas they were present in the invasion area of cancer cells from the LN sinus to the LN parenchyma. In the macro-Met-LNs, there were abundant α-SMA-positive cells that were also positive for PDGFR-β and Thy-1 but negative for fibulin-2 and fascin. Thus, regarding the expression of molecular markers, CAFs at the primary site of ICC are similar to PFs and different from those of HSCs or CAFs in the Met-LNs. CAFs at the primary sites and in the Met-LN are thought to be derived from PFs/BMDFs and resident cells of LNs, respectively.

Revisiting the dynamic cancer stem cell model: Importance of tumour edges

The lack of an effective treatment against cancer is not only due to its huge heterogeneity, but also to the fact that we don't have an answer to the question on how cancer originates. Among the proposed models to explain the development of cancer, the hierarchical model has been widely accepted. Nevertheless, this model fails to explain several experimental observations such as the cancer stem cells (CSCs) location inside a tumour or the differences between primary and metastatic tumours. Moreover, increasing evidence shows that the CSC phenotype is not a rigid state. Here, we present a critical review on the assumed tumour development models emphasizing the relevance of the dynamic and changing nature of cancer and the CSCs population in which the tumour microenvironment plays a crucial role and we propose a new model of tumour origin that could have an impact on new therapeutic strategies.

Recent advances in understanding the complexities of metastasis

Tumour metastasis is a dynamic and systemic process. It is no longer seen as a tumour cell-autonomous program but as a multifaceted and complex series of events, which is influenced by the intrinsic cellular mutational burden of cancer cells and the numerous bidirectional interactions between malignant and non-malignant cells and fine-tuned by the various extrinsic cues of the extracellular matrix. In cancer biology, metastasis as a process is one of the most technically challenging aspects of cancer biology to study. As a result, new platforms and technologies are continually being developed to better understand this process. In this review, we discuss some of the recent advances in metastasis and how the information gleaned is re-shaping our understanding of metastatic dissemination.

Recent advances in understanding the complexities of metastasis

Tumour metastasis is a dynamic and systemic process. It is no longer seen as a tumour cell-autonomous program but as a multifaceted and complex series of events, which is influenced by the intrinsic cellular mutational burden of cancer cells and the numerous bidirectional interactions between malignant and non-malignant cells and fine-tuned by the various extrinsic cues of the extracellular matrix. In cancer biology, metastasis as a process is one of the most technically challenging aspects of cancer biology to study. As a result, new platforms and technologies are continually being developed to better understand this process. In this review, we discuss some of the recent advances in metastasis and how the information gleaned is re-shaping our understanding of metastatic dissemination.

Endoglin Expression on Cancer-Associated Fibroblasts Regulates Invasion and Stimulates Colorectal Cancer Metastasis

PURPOSE

Cancer-associated fibroblasts (CAF) are a major component of the colorectal cancer tumor microenvironment. CAFs play an important role in tumor progression and metastasis, partly through TGF-β signaling pathway. We investigated whether the TGF-β family coreceptor endoglin is involved in CAF-mediated invasion and metastasis.

EXPERIMENTAL DESIGN

CAF-specific endoglin expression was studied in colorectal cancer resection specimens using IHC and related to metastases-free survival. Endoglin-mediated invasion was assessed in vitro by transwell invasion, using primary colorectal cancer-derived CAFs. Effects of CAF-specific endoglin expression on tumor cell invasion were investigated in a colorectal cancer zebrafish model, whereas liver metastases were assessed in a mouse model.

RESULTS

CAFs specifically at invasive borders of colorectal cancer express endoglin and increased expression intensity correlated with increased disease stage. Endoglin-expressing CAFs were also detected in lymph node and liver metastases, suggesting a role in colorectal cancer metastasis formation. In stage II colorectal cancer, CAF-specific endoglin expression at invasive borders correlated with poor metastasis-free survival. In vitro experiments revealed that endoglin is indispensable for bone morphogenetic protein (BMP)-9-induced signaling and CAF survival. Targeting endoglin using the neutralizing antibody TRC105 inhibited CAF invasion in vitro. In zebrafish, endoglin-expressing fibroblasts enhanced colorectal tumor cell infiltration into the liver and decreased survival. Finally, CAF-specific endoglin targeting with TRC105 decreased metastatic spread of colorectal cancer cells to the mouse liver.

CONCLUSIONS

Endoglin-expressing CAFs contribute to colorectal cancer progression and metastasis. TRC105 treatment inhibits CAF invasion and tumor metastasis, indicating an additional target beyond the angiogenic endothelium, possibly contributing to beneficial effects reported during clinical evaluations.See related commentary by Becker and LeBleu, p. 6110.