Guidelines and definitions for research on epithelial-mesenchymal transition.

Epithelial-mesenchymal transition (EMT) encompasses dynamic changes in cellular organization from epithelial to mesenchymal phenotypes, which leads to functional changes in cell migration and invasion. EMT occurs in a diverse range of physiological and pathological conditions and is driven by a conserved set of inducing signals, transcriptional regulators and downstream effectors. With over 5,700 publications indexed by Web of Science in 2019 alone, research on EMT is expanding rapidly. This growing interest warrants the need for a consensus among researchers when referring to and undertaking research on EMT. This Consensus Statement, mediated by 'the EMT International Association' (TEMTIA), is the outcome of a 2-year-long discussion among EMT researchers and aims to both clarify the nomenclature and provide definitions and guidelines for EMT research in future publications. We trust that these guidelines will help to reduce misunderstanding and misinterpretation of research data generated in various experimental models and to promote cross-disciplinary collaboration to identify and address key open questions in this research field. While recognizing the importance of maintaining diversity in experimental approaches and conceptual frameworks, we emphasize that lasting contributions of EMT research to increasing our understanding of developmental processes and combatting cancer and other diseases depend on the adoption of a unified terminology to describe EMT.

TGFß1 Stimulates Lymphatic Endothelial Cells to Produce IL7 and IL15, Which Act as Chemotactic Factors for Breast Cancer Cells with Mesenchymal Properties.

The lymphatic system is a major gateway for tumor cell dissemination but the mechanisms of how tumor cells gain access to lymphatic vessels are not completely understood. Breast cancer cells undergoing epithelial-mesenchymal transition (EMT) gain invasive and migratory properties. Overexpression of the cytokine transforming growth factor ß1 (TGFß1), a potent inducer of EMT, is frequently detected in the tumor microenvironment and correlates with invasion and lymph metastasis. Recently, we reported that TGFß1 stimulated breast cancer cells with mesenchymal properties to migrate in a targeted fashion towards the lymphatic system via CCR7/CCL21-mediated chemotaxis, similar to dendritic cells during inflammation. Here, we aimed to identify additional chemotactic factors and corresponding receptors that could be involved in guiding breast cancer cells through the lymphatic system. Through a combination of RNA sequencing analysis, database screening and invasion assays we identified IL7/IL7R and IL15/IL15R as pairs of chemokines and receptors with potential roles in promoting chemotactic migration of breast cancer cells with mesenchymal properties towards the lymphatics. The results demonstrate the capacity of TGFß1 to orchestrate crosstalk between tumor cells and lymphatic endothelial cells and warrant further studies to explore the roles of IL7 and IL15 in promoting lymph metastasis of breast cancer.

Sex dimorphism in the tumor microenvironment - From bench to bedside and back.

Cancer represents a significant cause of death and suffering in both the developed and developing countries. Key underlying issues in the mortality of cancer are delayed diagnosis and resistance to treatments. However, improvements in biomarkers represent one important step that can be taken for alleviating the suffering caused by malignancy. Precision-based medicine is promising for revolutionizing diagnostic and treatment strategies for cancer patients worldwide. Contemporary methods, including various omics and systems biology approaches, as well as advanced digital imaging and artificial intelligence, allow more accurate assessment of tumor characteristics at the patient level. As a result, treatment strategies can be specifically tailored and adapted for individual and/or groups of patients that carry certain tumor characteristics. This includes immunotherapy, which is based on characterization of the immunosuppressive tumor microenvironment (TME) and, more specifically, the presence and activity of immune cell subsets. Unfortunately, while it is increasingly clear that gender strongly affects immune regulation and response, there is a knowledge gap concerning differences in sex-specific immune responses and how these contribute to the immunosuppressive TME and the response to immunotherapy. In fact, sex dimorphism is poorly understood in cancer progression and is typically ignored in current clinical practice. In this review, we aim to survey the available literature and highlight the existing knowledge gap in order to encourage further studies that would contribute to understanding both gender-biased immunosuppression in the TME and the driver of tumor progression towards invasive and metastatic disease. The review highlights the need to include sex optimized/genderized medicine as a new concept in future medicine cancer diagnostics and treatments.

Induction of the Coxsackievirus and Adenovirus Receptor in Macrophages During the Formation of Atherosclerotic Plaques.

Multiple viruses are implicated in atherosclerosis, but the mechanisms by which they infect cells and contribute to plaque formation in arterial walls are not well understood. Based on reports showing the presence of enterovirus in atherosclerotic plaques we hypothesized that the coxsackievirus and adenovirus receptor (CXADR/CAR), although absent in normal arteries, could be induced during plaque formation. Large-scale microarray and mass spectrometric analyses revealed significant up-regulation of CXADR messenger RNA and protein levels in plaque-invested carotid arteries compared with control arteries. Macrophages were identified as a previously unknown cellular source of CXADR in human plaques and plaques from Ldr-/-Apob100/100 mice. CXADR was specifically associated with M1-polarized macrophages and foam cells and was experimentally induced during macrophage differentiation. Furthermore, it was significantly correlated with receptors for other viruses linked to atherosclerosis. The results show that CXADR is induced in macrophages during plaque formation, suggesting a mechanism by which enterovirus infect cells in atherosclerotic plaques.

Excessive vascular sprouting underlies cerebral hemorrhage in mice lacking αVß8-TGFß signaling in the brain.

Vascular development of the central nervous system and blood-brain barrier (BBB) induction are closely linked processes. The role of factors that promote endothelial sprouting and vascular leak, such as vascular endothelial growth factor A, are well described, but the factors that suppress angiogenic sprouting and their impact on the BBB are poorly understood. Here, we show that integrin αVß8 activates angiosuppressive TGFß gradients in the brain, which inhibit endothelial cell sprouting. Loss of αVß8 in the brain or downstream TGFß1-TGFBR2-ALK5-Smad3 signaling in endothelial cells increases vascular sprouting, branching and proliferation, leading to vascular dysplasia and hemorrhage. Importantly, BBB function in Itgb8 mutants is intact during early stages of vascular dysgenesis before hemorrhage. By contrast, Pdgfb(ret/ret) mice, which exhibit severe BBB disruption and vascular leak due to pericyte deficiency, have comparatively normal vascular morphogenesis and do not exhibit brain hemorrhage. Our data therefore suggest that abnormal vascular sprouting and patterning, not BBB dysfunction, underlie developmental cerebral hemorrhage.

Pericytes contribute to airway remodeling in a mouse model of chronic allergic asthma.

Myofibroblast accumulation, subepithelial fibrosis, and vascular remodeling are complicating features of chronic asthma, but the mechanisms are not clear. Platelet-derived growth factors (PDGFs) regulate the fate and function of various mesenchymal cells and have been implicated as mediators of lung fibrosis. However, it is not known whether PDGF-BB signaling via PDGFRß, which is critical for the recruitment of pericytes to blood vessels, plays a role in airway remodeling in chronic asthma. In the present study, we used a selective PDGFRß inhibitor (CP-673451) to investigate the role of PDGFRß signaling in the development of airway remodeling and lung dysfunction in an established mouse model of house dust mite-induced chronic allergic asthma. Unexpectedly, we found that pharmacological inhibition of PDGFRß signaling in the context of chronic aeroallergen exposure led to exacerbated lung dysfunction and airway smooth muscle thickening. Further studies revealed that the inflammatory response to aeroallergen challenge in mice was associated with decreased PDGF-BB expression and the loss of pericytes from the airway microvasculature. In parallel, cells positive for pericyte markers accumulated in the subepithelial region of chronically inflamed airways. This process was exacerbated in animals treated with CP-673451. The results indicate that perturbed PDGF-BB/PDGFRß signaling and pericyte accumulation in the airway wall may contribute to airway remodeling in chronic allergic asthma.

TGF-ß-induced epithelial-mesenchymal transition: a link between cancer and inflammation.

Metastatic spread of tumor cells to vital organs is the major cause of death in cancer. Accumulating data support an important role of infiltrating immune cells in promoting carcinoma progression into metastatic disease. Tumor-infiltrating immune cells produce and secrete cytokines, growth factors and proteases that re-activate latent developmental processes including epithelial-mesenchymal transition (EMT). EMT provides tumor cells with invasive, migratory and stem cell properties allowing them to disseminate and propagate at distant sites. Induction of EMT requires two criteria to be fulfilled: (i) cells are competent to undergo EMT (ii) an EMT-permissive microenvironment exists. The cytokine TGF-ß, which is expressed by tumor-infiltrating immune cells, stands out as a master regulator of the pro-invasive tumor microenvironment. TGF-ß cooperates with stem cell pathways, such as Wnt and Ras signaling, to induce EMT. In addition, TGF-ß contributes to an EMT-permissive microenvironment by switching the phenotypes of tumor-infiltrating immune cells, which thereby mount pro-invasive and pro-metastatic immune responses. In this review, we discuss the role of TGF-ß-induced EMT as a link between cancer and inflammation in the context of questions, which from our point of view are key to answer in order to understand the functionality of EMT in tumors.

Functionally specialized junctions between endothelial cells of lymphatic vessels.

Recirculation of fluid and cells through lymphatic vessels plays a key role in normal tissue homeostasis, inflammatory diseases, and cancer. Despite recent advances in understanding lymphatic function (Alitalo, K., T. Tammela, and T.V. Petrova. 2005. Nature. 438:946-953), the cellular features responsible for entry of fluid and cells into lymphatics are incompletely understood. We report the presence of novel junctions between endothelial cells of initial lymphatics at likely sites of fluid entry. Overlapping flaps at borders of oak leaf-shaped endothelial cells of initial lymphatics lacked junctions at the tip but were anchored on the sides by discontinuous button-like junctions (buttons) that differed from conventional, continuous, zipper-like junctions (zippers) in collecting lymphatics and blood vessels. However, both buttons and zippers were composed of vascular endothelial cadherin (VE-cadherin) and tight junction-associated proteins, including occludin, claudin-5, zonula occludens-1, junctional adhesion molecule-A, and endothelial cell-selective adhesion molecule. In C57BL/6 mice, VE-cadherin was required for maintenance of junctional integrity, but platelet/endothelial cell adhesion molecule-1 was not. Growing tips of lymphatic sprouts had zippers, not buttons, suggesting that buttons are specialized junctions rather than immature ones. Our findings suggest that fluid enters throughout initial lymphatics via openings between buttons, which open and close without disrupting junctional integrity, but most leukocytes enter the proximal half of initial lymphatics.

Pericyte requirement for anti-leak action of angiopoietin-1 and vascular remodeling in sustained inflammation.

Blood vessel leakiness is an early, transient event in acute inflammation but can also persist as vessels undergo remodeling in sustained inflammation. Angiopoietin/Tie2 signaling can reduce the leakiness through changes in endothelial cells. The role of pericytes in this action has been unknown. We used the selective PDGF-B-blocking oligonucleotide aptamer AX102 to determine whether disruption of pericyte-endothelial crosstalk alters vascular leakiness or remodeling in the airways of mice under four different conditions: i) baseline, ii) acute inflammation induced by bradykinin, iii) sustained inflammation after 7-day infection by the respiratory pathogen Mycoplasma pulmonis, or iv) leakage after bradykinin challenge in the presence of vascular stabilization by the angiopoietin-1 (Ang1) mimic COMP-Ang1 for 7 days. AX102 reduced pericyte coverage but did not alter the leakage of microspheres from tracheal blood vessels at baseline or after bradykinin; however, AX102 exaggerated leakage at 7 days after M. pulmonis infection and increased vascular remodeling and disease severity at 14 days. AX102 also abolished the antileakage effect of COMP-Ang1 at 7 days. Together, these findings show that pericyte contributions to endothelial stability have greater dependence on PDGF-B during the development of sustained inflammation, when pericyte dynamics accompany vascular remodeling, than under baseline conditions or in acute inflammation. The findings also show that the antileakage action of Ang1 requires PDGF-dependent actions of pericytes in maintaining endothelial stability.

Angiopoietin/Tie2 signaling transforms capillaries into venules primed for leukocyte trafficking in airway inflammation.

Vascular endothelial growth factor (VEGF) is a key angiogenic factor in tumors, but less is known about what drives vascular remodeling in inflammation, where plasma leakage and leukocyte influx are prominent features. In chronic airway inflammation in mice infected by the bacterium Mycoplasma pulmonis (M. pulmonis), the segment of the microvasculature that supports leukocyte adhesion and migration expands through remodeling of capillaries into vessels with features of venules. Here, we report that the angiopoietin/Tie2 pathway is an essential driving force for capillary remodeling into venules in M. pulmonis-infected mouse airways. Similar to M. pulmonis infection, systemic overexpression of angiopoietin-1 (Ang1) resulted in remodeling of airway capillaries into venular-like vessels that expressed venous markers like P-selectin, ICAM-1, and EphB4 and were sites of leukocyte adhesion during lipopolysaccharide-induced acute inflammation. Ang1 and Ang2 protein increased in M. pulmonis-infected mouse airways but came from different cellular sources: Ang1 was expressed in infiltrating neutrophils and Ang2 in endothelial cells. Indeed, systemic administration of soluble Tie2 inhibited capillary remodeling, induction of venous markers, and leukocyte influx in M. pulmonis-infected mouse airways. Together, these findings suggest that blockade of the Ang/Tie2 pathway may represent a therapeutic approach in airway inflammation.

Angiopoietin-2-driven vascular remodeling in airway inflammation.

Vascular remodeling is a feature of chronic inflammation during which capillaries transform into venules that expand the region of the vasculature in which leakage and leukocyte emigration both occur. Recently, we found that angiopoietin/Tie2 receptor signaling drives the transformation of capillaries into venules at an early stage of the sustained inflammatory response in the airways of mice infected with Mycoplasma pulmonis. However, the precise contributions of both angiopoietin-1 (Ang1) and angiopoietin-2 (Ang2) are not clear. In this study, we sought to determine the contribution of Ang2 to this vascular remodeling. Ang2 mRNA expression levels increased and phosphorylated Tie2 immunoreactivity in mucosal blood vessels decreased, indicative of diminished receptor signaling after infection. Selective inhibition of Ang2 throughout the infection by administration of either of two distinct function-blocking antibodies reduced the suppression of Tie2 phosphorylation and decreased the remodeling of mucosal capillaries into venules, the amount of leukocyte influx, and disease severity. These findings are consistent with Ang2 acting as an antagonist of Tie2 receptors and the reduction of Tie2 phosphorylation in endothelial cells rendering the vasculature more responsive to cytokines that promote both vascular remodeling and the consequences of inflammation after M. pulmonis infection. By blocking such changes, Ang2 inhibitors may prove beneficial in the treatment of sustained inflammation in which vascular remodeling, leakage, and leukocyte influx contribute to its pathophysiology.

Nuclear Syndecan-1 Regulates Epithelial-Mesenchymal Plasticity in Tumor Cells.

Tumor cells undergoing epithelial-mesenchymal transition (EMT) lose cell surface adhesion molecules and gain invasive and metastatic properties. EMT is a plastic process and tumor cells may shift between different epithelial-mesenchymal states during metastasis. However, how this is regulated is not fully understood. Syndecan-1 (SDC1) is the major cell surface proteoglycan in epithelial cells and has been shown to regulate carcinoma progression and EMT. Recently, it was discovered that SDC1 translocates into the cell nucleus in certain tumor cells. Nuclear SDC1 inhibits cell proliferation, but whether nuclear SDC1 contributes to the regulation of EMT is not clear. Here, we report that loss of nuclear SDC1 is associated with cellular elongation and an E-cadherin-to-N-cadherin switch during TGF-ß1-induced EMT in human A549 lung adenocarcinoma cells. Further studies showed that nuclear translocation of SDC1 contributed to the repression of mesenchymal and invasive properties of human B6FS fibrosarcoma cells. The results demonstrate that nuclear translocation contributes to the capacity of SDC1 to regulate epithelial-mesenchymal plasticity in human tumor cells and opens up to mechanistic studies to elucidate the mechanisms involved.

Different Regulation of Glut1 Expression and Glucose Uptake during the Induction and Chronic Stages of TGFß1-Induced EMT in Breast Cancer Cells.

Transforming growth factor beta 1 (TGF-ß1) is associated with epithelial-mesenchymal transition (EMT), lymph metastasis, and poor prognosis in breast cancer. Paradoxically, TGF-ß1 is also a potent inhibitor of cell proliferation. TGF-ß1-induced EMT involves activation of several pathways including AKT, which also regulates glucose uptake. Recent data show that prolonged TGF-ß1 exposure leads to a more stable EMT phenotype in breast cancer cells. However, whether this is linked to changes in glucose metabolism is not clear. Here, we used a model of TGF-ß1-induced EMT in mammary epithelial cells to study the regulation of Glut1 and EMT markers during the induction compared to a prolonged phase of EMT by western blot, immunofluorescence and qPCR analysis. We also measured cell proliferation and uptake of the glucose analogue 2-NDBG. We found that EMT induction was associated with decreased Glut1 expression and glucose uptake. These effects were linked to reduced cell proliferation rather than EMT. Knockdown of Glut1 resulted in growth inhibition and less induction of vimentin during TGF-ß1-induced EMT. Intriguingly, Glut1 levels, glucose uptake and cell proliferation were restored during prolonged EMT. The results link Glut1 repression to the anti-proliferative response of TGF-ß1 and indicate that re-expression of Glut1 during chronic TGF-ß1 exposure allows breast cancer cells to develop stable EMT and proliferate, in parallel.

Mapping the Interactome of the Nuclear Heparan Sulfate Proteoglycan Syndecan-1 in Mesothelioma Cells.

Syndecan-1 (SDC1) is a cell surface heparan sulfate proteoglycan (HSPG), which regulates various signaling pathways controlling the proliferation and migration of malignant mesothelioma and other types of cancer. We have previously shown that SDC1 can translocate to the nucleus in mesothelioma cells through a tubulin-dependent transport mechanism. However, the role of nuclear SDC1 is largely unknown. Here, we performed co-immunoprecipitation (Co-IP) of SDC1 in a mesothelioma cell line to identify SDC1 interacting proteins. The precipitates contained a large number of proteins, indicating the recovery of protein networks. Proteomic analysis with a focus on nuclear proteins revealed an association with pathways related to cell proliferation and RNA synthesis, splicing and transport. In support of this, the top RNA splicing candidates were verified to interact with SDC1 by Co-IP and subsequent Western blot analysis. Further loss- and gain-of-function experiments showed that SDC1 influences RNA levels in mesothelioma cells. The results identify a proteomic map of SDC1 nuclear interactors in a mesothelioma cell line and suggest a previously unknown role for SDC1 in RNA biogenesis. The results should serve as a fundament for further studies to discover the role of nuclear SDC1 in normal and cancer cells of different origin.

Mutant CFTR Drives TWIST1 mediated epithelial-mesenchymal transition.

Cystic fibrosis (CF) is a monogenetic disease resulting from mutations in the Cystic Fibrosis Transmembrane conductance Regulator (CFTR) gene encoding an anion channel. Recent evidence indicates that CFTR plays a role in other cellular processes, namely in development, cellular differentiation and wound healing. Accordingly, CFTR has been proposed to function as a tumour suppressor in a wide range of cancers. Along these lines, CF was recently suggested to be associated with epithelial-mesenchymal transition (EMT), a latent developmental process, which can be re-activated in fibrosis and cancer. However, it is unknown whether EMT is indeed active in CF and if EMT is triggered by dysfunctional CFTR itself or a consequence of secondary complications of CF. In this study, we investigated the occurrence of EMT in airways native tissue, primary cells and cell lines expressing mutant CFTR through the expression of epithelial and mesenchymal markers as well as EMT-associated transcription factors. Transepithelial electrical resistance, proliferation and regeneration rates, and cell resistance to TGF-ß1induced EMT were also measured. CF tissues/cells expressing mutant CFTR displayed several signs of active EMT, namely: destructured epithelial proteins, defective cell junctions, increased levels of mesenchymal markers and EMT-associated transcription factors, hyper-proliferation and impaired wound healing. Importantly, we found evidence that the mutant CFTR triggered EMT was mediated by EMT-associated transcription factor TWIST1. Further, our data show that CF cells are over-sensitive to EMT but the CF EMT phenotype can be reversed by CFTR modulator drugs. Altogether, these results identify for the first time that EMT is intrinsically triggered by the absence of functional CFTR through a TWIST1 dependent mechanism and indicate that CFTR plays a direct role in EMT protection. This mechanistic link is a plausible explanation for the high incidence of fibrosis and cancer in CF, as well as for the role of CFTR as tumour suppressor protein.

Estrogen receptor-beta expression in human laryngeal carcinoma: correlation with the expression of epithelial-mesenchymal transition specific biomarkers.

Laryngeal carcinoma is a malignancy of the respiratory tract with a significantly higher male to female ratio, suggesting involvement of gender-depended factors in the pathogenesis. Estrogen influences the pathological processes of hormone-dependent cancers, such as breast, prostate and ovarian cancers, through its receptors, estrogen receptor-alpha (ER-alpha) and -beta (ER-beta). While ER-alpha promotes cell proliferation, recent studies indicate that ER-beta is protective against carcinoma progression into an invasive state. However, it is unclear whether ER-beta plays a role in laryngeal cancer. In the present study we examined the expression of ER-beta in 80 invasive human squamous laryngeal carcinomas by immunohistochemistry and correlated ER-beta expression with markers of epithelial-mesenchymal transition (EMT). ER-beta was expressed in 83% of tumour specimens where it was localized in the nuclei of tumour cells. The expression of ER-beta correlated positively with the maintenance of E-cadherin and beta-catenin at cell junctions and negatively with the loss of E-cadherin, nuclear translocation of beta-catenin and increased TNM stage. We concluded that estrogen receptor-beta expression is documented in laryngeal cancer indicating a possible role in the pathogenesis of this malignancy. It is suggested that ER-beta could protect tumour cells from acquiring aggressive EMT features such as E-cadherin downregulation and nuclear beta-catenin activation.

CXADR-Mediated Formation of an AKT Inhibitory Signalosome at Tight Junctions Controls Epithelial-Mesenchymal Plasticity in Breast Cancer.

Tight junctions (TJ) act as hubs for intracellular signaling pathways controlling epithelial cell fate and function. Deregulation of TJ is a hallmark of epithelial-mesenchymal transition (EMT), which contributes to carcinoma progression and metastasis. However, the signaling mechanisms linking TJ to the induction of EMT are not understood. Here, we identify a TJ-based signalosome, which controls AKT signaling and EMT in breast cancer. The coxsackie and adenovirus receptor (CXADR), a TJ protein with an essential yet uncharacterized role in organogenesis and tissue homeostasis, was identified as a key component of the signalosome. CXADR regulated the stability and function of the phosphatases and AKT inhibitors PTEN and PHLPP2. Loss of CXADR led to hyperactivation of AKT and sensitized cells to TGFß1-induced EMT. Conversely, restoration of CXADR stabilized PHLPP2 and PTEN, inhibited AKT, and promoted epithelial differentiation. Loss of CXADR in luminal A breast cancer correlated with loss of PHLPP2 and PTEN and poor prognosis. These results show that CXADR promotes the formation of an AKT-inhibitory signalosome at TJ and regulates epithelial-mesenchymal plasticity in breast cancer cells. Moreover, loss of CXADR might be used as a prognostic marker in luminal breast cancer. SIGNIFICANCE: The tight junction protein CXADR controls epithelial-mesenchymal plasticity in breast cancer by stabilizing the AKT regulators PTEN and PHLPP2.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/1/47/F1.large.jpg.

Epithelial-mesenchymal transition in cancer metastasis through the lymphatic system.

It was already in the 18th century when the French surgeon LeDran first noted that breast cancer patients with spread of tumor cells to their axillary lymph nodes had a drastically worse prognosis than patients without spread (LeDran et al., ). Since then, metastatic spread of cancer cells to regional lymph nodes has been established as the most important prognostic factor in many types of cancer (Carter et al., ; Elston and Ellis, ). However, despite its clinical importance, lymph metastasis remains an underexplored area of tumor biology. Fundamental questions, such as when, how, and perhaps most importantly, why tumor cells disseminate through the lymphatic system, remain largely unanswered. Accordingly, no treatment strategies exist that specifically target lymph metastasis. The identification of epithelial-mesenchymal transition (EMT) as a mechanism, which allows cancer cells to dedifferentiate and acquire enhanced migratory and invasive properties, has been a game changer in cancer research. Conceptually, EMT provides an explanation for why epithelial cancers with poor differentiation status are generally more aggressive and prone to metastasize than more differentiated cancers. Inflammatory cytokines, such as TGF-ß, which are produced and secreted by tumor-infiltrating immune cells, are potent inducers of EMT. Thus, reactivation of EMT also links cancer-related inflammation to invasive and metastatic disease. Recently, we found that breast cancer cells undergoing TGF-ß-induced EMT acquire properties of immune cells allowing them to disseminate in a targeted fashion through the lymphatic system similar to activated dendritic cells during inflammation. Here, we review our current understanding of the mechanisms by which cancer cells spread through the lymphatic system and the links to inflammation and the immune system. We also emphasize how imaging techniques have the potential to further expand our knowledge of the mechanisms of lymph metastasis, and how lymph nodes serve as an interface between cancer and the immune system.