Comprehensive analysis of prognostic immune-related genes in the tumor microenvironment of hepatocellular carcinoma (HCC)

Growing evidence supports that the tumor microenvironment plays a key role in the development and progression of tumors. But immune microenvironment of hepatocellular carcinoma (HCC) has not yet been fully explored. In the present investigation, the clinical value and prognostic significance of immune-related genes in HCC were investigated.The immune and stromal scores of HCC were calculated through the application of Estimation of Stromal and Immune cells in Malignant Tumor tissues using Expression data Algorithm based on the Cancer Genome Atlas database. Differentially expressed genes were identified using the “edgeR” package of the R software. Functional annotation and pathway enrichment were performed using “ggplots2” and “clusterProfiler” packages in R software. Protein-protein interaction network was constructed using STRING, and the hub genes were identified through the Cytoscape. Survival analysis was performed using Kaplan-Meier methods. Tumor Immune Estimation Resource algorithm was used to view the immune landscape of the microenvironment in HCC.Firstly, the immune and stromal scores of HCC were calculated and we found that the immune and stromal scores of HCC were closely related to the patients’ prognosis. Then the differentially expressed genes were identified respectively stratified by the median value of the immune and stromal scores, and the immune-related genes that related to the prognosis in HCC patients were further identified. Functional enrichment analysis and protein-protein interaction networks further showed that these genes mainly participated in immune-related biological process. In addition, dendritic cells were found to be the most abundant in the microenvironment of HCC through Tumor Immune Estimation Resource algorithm and were significantly associated with the patients’ prognosis. To robust the results, the immune-related genes were validated in an independent dataset from the Gene Expression Omnibus database.We arrived at a more comprehensive understanding of the microenvironment of HCC and extracted 7 immune-related genes that were significantly associated with the recurrence survival of HCC.     

Pancreatic cancer stroma: controversies and current insights

Pancreatic cancer is characterized by a dense stromal response. The stroma includes a heterogeneous mass of cells, including pancreatic stellate cells, fibroblasts, immune cells and nerve cells, as well as extracellular matrix proteins, cytokines and growth factors, which interact with the tumor cells. Previous research has indicated that stromal elements contribute to tumor growth and aggressiveness. However, recent studies suggest that some elements of the stroma may actually restrain the tumor. This review focuses on the complex interactions between the stromal microenvironment and tumor cells, discussing molecular mechanisms and potential future diagnostic and therapeutic approaches by targeting the stroma.     

Intrinsic modulation of lymphocyte function by stromal cell network: advance in therapeutic targeting of cancer

Advances in tumor biology have demonstrated a point of critical importance: tumor are established as an intersection of malignant clone cells and surrounding stromal cells. The stroma is composed of nonhematopoietic cells, including connective tissue cells, blood vessels, nerves, fat and smooth muscle cells, in the extracellular matrix niche. Recent studies have demonstrated that stromal cells regulate immune responses by: coordinating lymphocyte homing, differentiation, activation and antigen responses; inducing tolerance; and maintaining immunologic memory. Hence, elucidation of the interaction between stromal cells and lymphocytes is essential for generating effective immunotherapies. In this article, we summarize what is currently known about the interactions between stromal cells and lymphocytes in the tumor microenvironment, as well as potential immunotherapeutic approaches targeting stroma-lymphocyte interactions; both in the context of our work on multiple myeloma, and of recent literature in both solid tumors and hematologic malignancies.     

Associations Between Elastography Findings and Clinicopathological Factors in Breast Cancer

This study aimed to explore the clinical significance of breast tumor tissue stiffness based on ultrasound elastographic evaluation in clinical breast cancer.Tumor tissue stiffness is mainly regulated by interactions among tumor cells, stromal cells, and extracellular matrix and was recently regarded as a representative feature of tumor microenvironment. Basic research has already revealed that the tumor stiffness can lead to tumor progression; however, little is known about its clinical significance because thus far, no useful modality is available in the clinical setting.We investigated the tumor stiffness by strain elastography in 503 consecutive patients with invasive breast cancer. Correlations between stiffness and clinicopathological factors, including tumor size, lymph node involvement, tumor subtypes, and stromal-related genes’ expressions in primary breast tumor, were statistically examined.We identified that clinical tumor stiffness significantly correlated with lymph node involvement and invasive tumor size but not with hormonal receptor expressions, human epidermal growth factor receptor type 2 status, and ki67 labeling index by analyses of both categorical and continuous variables of stiffness. On multivariate analyses, axillary lymph node metastasis was an independent factor that influenced the stiffness of primary breast tumor. In the gene expression analyses, relatively hard tumors had a significantly high gene expression of lysyl oxidase compared with soft tumors.Our study showed a close relationship between primary tumor stiffness by elastographic evaluation and lymph node involvement in clinical breast cancer. Further investigations on tumor-related tissue stiffness are required.     

Stromal-epithelial interactions in the progression of ovarian cancer: influence and source of tumor stromal cells

Stromal cells are essential for the progression of many cancers including ovarian tumors. Stromal cell-epithelial cell interactions are important for tumor development, growth, angiogenesis, and metastasis. In the current study, the effects of normal ovarian bovine stromal cells on ovarian tumor progression was investigated. The hypothesis tested is that ovarian stromal cells will alter the onset and progression of ovarian tumors. Conditioned medium from normal bovine ovarian surface stromal cells was found to stimulate the growth of normal ovarian surface epithelium and had no effect on the growth of human tumor cell lines SKOV3 and OCC1. Human ovarian cancer cell lines, SKOV3 and OCC1, were injected subcutaneously into nude mice to examine tumor progression. Tumor growth in the nude mice was dramatically reduced when normal ovarian surface stromal cells were co-injected with SKOV3 or OCC1 cells. Similar results were obtained with normal bovine or human ovarian stromal cells. In contrast, irrelevant testicular stromal cells and epithelial cells had no effect on tumor growth in the nude mouse. Histological examination of these tumors revealed a characteristic stromal cell component adjacent to epithelial cell colonies. Sections of these tumors were hybridized with species specific genomic probes using fluorescence in situ hybridization to identify cell populations. Epithelial cells were shown to be of human origin (i.e. SKOV3 or OCC1), but stromal cells were found to be primarily murine in origin (i.e. host tissue). No detectable bovine cells were observed in the tumors after one week post-injection. Results suggest that stromal cells are an essential component of ovarian tumors. Interestingly, normal ovarian stromal cells had the ability to inhibit tumor growth, but were not able to survive long-term incubation at the tumor site. The developing tumor appears to recruit host (i.e. murine) stromal cells to invade the tumor and support its growth. In summary, normal ovarian stromal cells can inhibit ovarian tumor progression and the developing tumors recruit adjacent host stroma to become "tumor stroma". The tumor stroma likely develop an altered phenotype that cooperates with the tumorigenic epithelial cells to help promote the progression of ovarian cancer.     

Mining immune-related genes with prognostic value in the tumor microenvironment of breast invasive ductal carcinoma

The tumor microenvironment (TME) plays an important role in the development of breast cancer. Due to limitations in experimental conditions, the molecular mechanism of TME in breast cancer has not yet been elucidated. With the development of bioinformatics, the study of TME has become convenient and reliable.Gene expression and clinical feature data were downloaded from The Cancer Genome Atlas database and the Molecular Taxonomy of Breast Cancer International Consortium database. Immune scores and stromal scores were calculated using the Estimation of Stromal and Immune Cells in Malignant Tumor Tissues Using Expression Data algorithm. The interaction of genes was examined with protein-protein interaction and co-expression analysis. The function of genes was analyzed by gene ontology enrichment analysis, Kyoto Encyclopedia of Genes and Genomes analysis and gene set enrichment analysis. The clinical significance of genes was assessed with Kaplan-Meier analysis and univariate/multivariate Cox regression analysis.Our results showed that the immune scores and stromal scores of breast invasive ductal carcinoma (IDC) were significantly lower than those of invasive lobular carcinoma. The immune scores were significantly related to overall survival of breast IDC patients and both the immune and stromal scores were significantly related to clinical features of these patients. According to the level of immune/stromal scores, 179 common differentially expressed genes and 5 hub genes with prognostic value were identified. In addition, the clinical significance of the hub genes was validated with data from the molecular taxonomy of breast cancer international consortium database, and gene set enrichment analysis analysis showed that these hub genes were mainly enriched in signaling pathways of the immune system and breast cancer.We identified five immune-related hub genes with prognostic value in the TME of breast IDC, which may partly determine the prognosis of breast cancer and provide some direction for development of targeted treatments in the future.     

Tumor microenvironment in primary liver tumors: A challenging role of natural killer cells

In the last years, several studies have been focused on elucidate the role of tumor microenvironment(TME) in cancer development and progression. Within TME, cells from adaptive and innate immune system are one of the main abundant components. The dynamic interactions between immune and cancer cells lead to the activation of complex molecular mechanisms that sustain tumor growth. This important cross-talk has been elucidate for several kind of tumors and occurs also in patients with liver cancer, such as hepatocellular carcinoma(HCC) and intrahepatic cholangiocarcinoma(iCCA). Liver is well-known to be an important immunological organ with unique microenvironment. Here, in normal conditions, the rich immune-infiltrating cells cooperate with non-parenchymal cells, such as liver sinusoidal endothelial cells and Kupffer cells, favoring self-tolerance against gut antigens. The presence of underling liver immunosuppressive microenvironment highlights the importance to dissect the interaction between HCC and iCCA cells with immune infiltrating cells, in order to understand how this cross-talk promotes tumor growth. Deeper attention is, in fact, focused on immune-based therapy for these tumors, as promising approach to counteract the intrinsic anti-tumor activity of this microenvironment. In this review, we will examine the key pathways underlying TME cell-cell communications, with deeper focus on the role of natural killer cells in primary liver tumors, such as HCC and iCCA, as new opportunities for immune-based therapeutic strategies.     

基于生物信息学探索肺鳞癌肿瘤微环境及寻找关键基因

目的探究肺鳞癌肿瘤微环境,并寻找影响肺鳞癌肿瘤微环境的关键基因。方法使用R语言ESTIMATE算法计算TCGA数据库中肺鳞癌样本的基质评分、免疫评分与综合评分;CIBERSORT算法计算肺鳞癌22种肿瘤浸润免疫细胞丰度。根据surv_cutpoint函数分别获得3种评分的最佳截断值并分为各自的高评分组与低评分组,进行3种评分的高评分组与低评分组5年限制平均生存时间分析及差异表达分析。将差异表达分析获取的基因定义为差异表达基因,再根据蛋白质相互作用网络和单因素Cox回归分析结果确定关键基因。最后,利用Timer数据库探索关键基因与肿瘤浸润免疫细胞之间的相互关系。结果肺鳞癌基质评分、免疫评分与综合评分均低于癌旁组织,差异均有统计学意义(P值均<0.001)。限制平均生存时间分析显示,随访5年,3种评分的高评分组均较低评分组预后差(P值均<0.05)。肺鳞癌组织中22种肿瘤浸润免疫细胞含量有18种与癌旁组织比较,差异均有统计学意义(P值均<0.05)。差异分析确定了影响肿瘤微环境的972个差异基因,将972个差异基因进行单因素Cox回归分析,确定了135个与生存相关的基因(P值均<0.05),与蛋白相互作用网络中前50个中枢基因进行交叉,获得3个与肿瘤微环境相关且影响肺鳞癌预后的关键基因AGTR2、CXCL2、ADORA1。最后Timer数据库探究显示关键基因表达量与肿瘤浸润免疫细胞具有相关性(P值均<0.05)。结论通过生物信息学探索了肺鳞癌肿瘤微环境,筛选出3个与肺鳞癌预后相关且影响肿瘤微环境的关键基因AGTR2、CXCL2、ADORA1,为肺鳞癌提供了潜在的治疗靶点。     

Emergence of immunotherapy as a novel way to treat hepatocellular carcinoma

Tumor immunity proceeds through multiple processes, which consist of antigen presentation by antigen presenting cells(APCs) to educate effector cells and destruction by the effector cytotoxic cells. However, tumor immunity is frequently repressed at tumor sites. Malignantly transformed cells rarely survive the attack by the immune system, but cells that do survive change their phenotypes to reduce their immunogenicity. The resultant cells evade the attack by the immune system and form clinically discernible tumors. Tumor microenvironments simultaneously contain a wide variety of immune suppressive molecules and cells to dampen tumor immunity. Moreover, the liver microenvironment exhibits immune tolerance to reduce aberrant immune responses to massively-exposed antigens via the portal vein, and immune dysfunction is frequently associated with liver cirrhosis, which is widespread in hepatocellular carcinoma(HCC) patients. Immune therapy aims to reduce tumor burden, but it is also expected to prevent non-cancerous liver lesions from progressing to HCC, because HCC develops or recurs from noncancerous liver lesions with chronic inflammatory states and/or cirrhosis and these lesions cannot be cured and/or eradicated by local and/or systemic therapies. Nevertheless, cancer immune therapy should augment specific tumor immunity by using two distinct measures: enhancing the effector cell functions such as antigen presentation capacity of APCs and tumor cell killing capacity of cytotoxic cells, and reactivating the immune system in immune-suppressive tumor microenvironments. Here, we will summarize the current status and discuss the future perspective on immune therapy for HCC.     

Malignant cells facilitate lung metastasis by bringing their own soil

Metastatic cancer cells (seeds) preferentially grow in the secondary sites with a permissive microenvironment (soil). We show that the metastatic cells can bring their own soil--stromal components including activated fibroblasts--from the primary site to the lungs. By analyzing the efferent blood from tumors, we found that viability of circulating metastatic cancer cells is higher if they are incorporated in heterotypic tumor-stroma cell fragments. Moreover, we show that these cotraveling stromal cells provide an early growth advantage to the accompanying metastatic cancer cells in the lungs. Consistent with this hypothesis, we demonstrate that partial depletion of the carcinoma-associated fibroblasts, which spontaneously spread to the lung tissue along with metastatic cancer cells, significantly decreases the number of metastases and extends survival after primary tumor resection. Finally, we show that the brain metastases from lung carcinoma and other carcinomas in patients contain carcinoma-associated fibroblasts, in contrast to primary brain tumors or normal brain tissue. Demonstration of the direct involvement of primary tumor stroma in metastasis has important conceptual and clinical implications for the colonization step in tumor progression.     

Involvement of RhoA in progression of human hepatocellular carcinoma

BACKGROUND AND AIM: The activation of Rho proteins has been shown to lead to loss of polarity in cancer cells, as well as reorganization of the cytoskeleton and facilitation of cell motility, possibly resulting in their malignant potential. The clinicopathological significance of RhoA, however, is not yet well known in the case of hepatocellular carcinoma (HCC). This study evaluated the clinicopathological correlation of RhoA levels with HCC. METHODS: The intratumor expression level of Rho was determined and compared with that in adjacent non-cancerous hepatic tissue using quantitative real time RT-PCR and Western blotting in 64 patients with HCC. Relationships between the level of RhoA and clinicopathological factors were examined. RhoA protein expression was confirmed by immunohistochemistry. RESULTS: RhoA immunostaining was strong in malignant tissue whereas it was minimal in benign tissue. Tumor tissue of HCC patients demonstrated a copy number of RhoA mRNA that was well correlated with its protein level in each case and was significantly higher than that found in the corresponding non-cancerous liver tissue (P < 0.01). With regard to venous invasion, satellite lesions and advanced pTNM stage, the RhoA level tended to be higher in HCC than that seen in negative tissue (P < 0.05). CONCLUSIONS: This is the first demonstration that the expression level of RhoA is correlated with tumor progression and metastasis in HCC. RhoA in tumor tissue might be expected to be not only a good candidate marker for invasive and proliferative tumor cells, but also a molecular target of these cells.     

Immunometabolism:A novel perspective of liver cancer microenvironment and its influence on tumor progression

The initiation and progression of liver cancer, including hepatocellular carcinoma and intrahepatic cholangiocarcinoma, are dependent on its tumor microenvironment. Immune cells are key players in the liver cancer microenvironment and show complicated crosstalk with cancer cells. Emerging evidence has shown that the functions of immune cells are closely related to cell metabolism. However, the effects of metabolic changes of immune cells on liver cancer progression are largely undefined. In this review, we summarize the recent findings of immunometabolism and relate these findings to liver cancer progression. We also explore the translation of the understanding of immunometabolism for clinical use.     

Bone morphogenetic protein antagonist gremlin 1 is widely expressed by cancer-associated stromal cells and can promote tumor cell proliferation

Although tissue microenvironments play critical roles in epithelial development and tumorigenesis, the factors mediating these effects are poorly understood. In this work, we used a genomic approach to identify factors produced by cells in the microenvironment of basal cell carcinoma (BCC) of the skin, one of the most common human cancers. The global gene expression programs of stromal cell cultures derived from human BCCs showed consistent, systematic differences from those derived from nontumor skin. The gene most consistently expressed at a higher level in BCC tumor stromal cells compared with those from nontumor skin was GREMLIN 1, which encodes a secreted antagonist of the bone morphogenetic protein (BMP) pathway. BMPs and their antagonists are known to play a crucial role in stem and progenitor cell biology as regulators of the balance between expansion and differentiation. Consistent with the hypothesis that BMP antagonists might have a similar role in cancer, we found GREMLIN 1 expression in the stroma of human BCC tumors but not in normal skin in vivo. Furthermore, BMP 2 and 4 are expressed by BCC cells. Ex vivo, BMP inhibits, and Gremlin 1 promotes, proliferation of cultured BCC cells. We further found that GREMLIN 1 is expressed by stromal cells in many carcinomas but not in the corresponding normal tissue counterparts that we examined. Our data suggest that BMP antagonists may be important constituents of tumor stroma, providing a favorable microenvironment for cancer cell survival and expansion in many cancers.     

Impaired tumor growth,metastasis, angiogenesis and wound healing in annexin A1-null mice

Despite 2 decades of research, no clear function for annexin A1 (AnxA1) has been established. Using AnxA1-KO mice, we show that tumor growth and metastasis are significantly decreased, whereas rodent survival and tumor necrosis are greatly increased when tumors grow in AnxA1-KO mice. Systems analysis of gene expression in these tumors specifically implicates 2 related vascular functions, angiogenesis and wound healing, in this impairment. Both tumor vascular development and wound healing are greatly retarded in KO tissues. Aortic ring assays reveal induced AnxA1 expression on sprouting endothelial cells of normal mice whereas KO aortas exhibit impaired endothelial cell sprouting that is rescued by adenoviral expression of AnxA1. Key differences in specific gene regulation may define new molecular pathways mediating angiogenesis, including a reset profile of pro- versus anti-angiogenic factors, apparently distinct for physiological versus pathological angiogenesis. These studies establish novel pro-angiogenic functions for AnxA1 in vascular endothelial cell sprouting, wound healing, and tumor growth and metastasis, thereby uncovering a new functional target for repairing damaged tissue and treating diseases such as cancer. They also provide critical new evidence that the tumor stroma and its microenvironment can greatly affect tumor progression and metastasis.     

Clinicopathology and prognosis of mucinous gastric carcinoma

BACKGROUND/AIMS: Mucinous gastric carcinoma (MGC) is a rare histopathological type of gastric carcinoma, for which the clinicopathological features and prognosis remain controversial. To clarify the clinical significance of mucinous histological type in gastric cancer, we studied clinicopathological characteristics of MGC tumors and prognosis of patients. METHODOLOGY: Forty-one patients with MGC and 1,407 patients with non-mucinous gastric carcinoma (NGC) were included in the study. Tumors were evaluated against patient gender and age, tumor location, size, and macroscopic type, depth of gastric wall invasion, lymph node metastasis, liver metastasis, peritoneal dissemination, distant metastasis, stage, and operative curability. RESULTS: Compared with NGC tumors, MGC tumors were larger, showed more serosal invasion, were associated with a higher incidence of lymph node metastasis, and peritoneal dissemination, and tended to be at a more advanced stage. However, multivariate analysis demonstrated that the mucinous histological type was neither an independent prognostic factor nor an independent risk factor for lymph node metastasis in patients with gastric cancer. CONCLUSIONS: The mucinous histological type had no influence on patient outcome or the frequency of lymph node metastasis. MGC tumors are therefore biologically similar to those in NGC.     

Alpha-smooth muscle actin-positive stromal cells in cholangiocarcinomas, hepatocellular carcinomas and metastatic liver carcinomas

Aims/Methods: In the human liver, α-smooth muscle actin (ASMA) is present in smooth muscle of the vasculature, perisinusoidal cell (Ito cells), and myofibroblasts derived from perisinusoidal cells. In this study, we investigated ASMA-positive stromal cells and their relation to tumor fibrosis in 50 cholangiocarcinomas, 30 hepatocellular carcinomas, and 57 metastatic liver carcinomas.Results: Tumor fibrosis was much more extensive in cholangiocarcinomas and metastatic liver carcinomas than in metastatic liver carcinomas. ASMA immunoreactivity was prominent in the sinusoids surrounding cancer nodules and in the cancerous stroma, not in sinusoids remote from cancer nodules. ASMA-positive stromal cells were divisible into peritumoral ASMA-positive perisinusoidal cells and intratumoral ASMA-positive stromal cells. Both types of ASMA-positive cells were abundant in cholangiocarcinomas and metastatic liver carcinomas, but much more scanty in hepatocellular carcinomas. The number of both types showed a significant positive correlation with the degree of tumor fibrosis. The peritumoral ASMA-positive perisinusoidal cells were frequently in direct continuity with intratumoral ASMA-positive stromal cells in cholangiocarcinomas and metastatic liver carcinomas.Conclusions: These findings show that ASMA-positive stromal cells are related to tumor fibrosis in liver malignancies. Although direct evidence is lacking, the data suggest that, in cholangiocarcinomas and metastatic liver carcinomas, peritumoral ASMA-positive perisinusoidal cells transform into activated perisinusoidal cells (myofibroblasts), are incorporated into the tumor (intratumoral ASMA-positive stromal cells), and produce extracellular matrix proteins, that lead to tumor fibrosis. The scantly ASMA-positive cells in hepatocellular carcinomas may in part be responsible for the small amount of fibrosis in this tumor.     

Stroma-targeting strategies in pancreatic cancer: Past lessons,challenges and prospects

Pancreatic ductal adenocarcinoma (PDAC) is projected to emerge as the second leading cause of cancer-related death after 2030. Extreme treatment resistance is perhaps the most significant factor that underlies the poor prognosis of PDAC. To date, combination chemotherapy remains the mainstay of treatment for most PDAC patients. Compared to other cancer types, treatment response of PDAC tumors to similar chemotherapy regimens is clearly much lower and shorter-lived. Aside from typically harboring genetic alterations that to date remain un-druggable and are drivers of treatment resistance, PDAC tumors are uniquely characterized by a densely fibrotic stroma that has well-established roles in promoting cancer progression and treatment resistance. However, emerging evidence also suggests that indiscriminate targeting and near complete depletion of stroma may promote PDAC aggressiveness and lead to detrimental outcomes. These conflicting results undoubtedly warrant the need for a more in-depth understanding of the heterogeneity of tumor stroma in order to develop modulatory strategies in favor of tumor suppression. The advent of novel techniques including single cell RNA sequencing and multiplex immunohistochemistry have further illuminated the complex heterogeneity of tumor cells, stromal fibroblasts, and immune cells. This new knowledge is instrumental for development of more refined therapeutic strategies that can ultimately defeat this disease. Here, we provide a concise review on lessons learned from past stroma-targeting strategies, new challenges revealed from recent preclinical and clinical studies, as well as new prospects in the treatment of PDAC.     

Hepatic stellate cells and extracellular matrix in hepatocellular carcinoma: more complicated than ever

Hepatocellular carcinoma (HCC) is the fifth most common cancer worldwide and the third leading cause of cancer death. Recent epidemiological data indicate that the mortality rate of HCC will double over the next decades in the USA and Europe. Liver cancer progresses in a large percentage of cases during the clinical course of chronic fibro‐inflammatory liver diseases leading to cirrhosis. Therefore, HCC development is regarded as the result of different environmental risk factors each involving different genetic, epigenetic‐ and chromosomal alterations and gene mutations. During tumour progression, the malignant hepatocytes and the activated hepatic stellate cells are accompanied by cancer‐associated fibroblasts, myofibroblasts and immune cells generally called tumour stromal cells. This new and dynamic milieu further enhances the responsiveness of tumour cells towards soluble mediators secreted by tumour stromal cells, thus directly affecting the malignant hepatocytes. This results in altered molecular pathways with cell proliferation as the most important mechanism of liver cancer progression. Given this contextual complexity, it is of utmost importance to characterize the molecular pathogenesis of HCC, and to identify the dominant pathways/drivers and aberrant signalling pathways. This will allow an effective therapy for HCC that should combine strategies affecting both cancer and the tumour stromal cells. This review provides an overview of the recent challenges and issues regarding hepatic stellate cells, extracellular matrix dynamics, liver fibrosis/cirrhosis and therapy, tumour microenvironment and HCC.     

Targeting the tumor stroma in hepatocellular carcinoma

Hepatocellular carcinoma(HCC) is one of the most common and deadly cancers worldwide. In ninety percent of the cases it develops as a result of chronic liver damage and it is thus a typical inflammationrelated cancer characterized by the close relation between the tumor microenvironment and tumor cells. The stromal environment consists out of several cell types, including hepatic stellate cells, macrophages and endothelial cells. They are not just active bystanders in the pathogenesis of HCC, but play an important and active role in tumor initiation, progression and metastasis. Furthermore, the tumor itself influences these cells to create a background that is beneficial for sustaining tumor growth. One of the key players is the hepatic stellate cell, which is activated during liver damage and differentiates towards a myofibroblast-like cell. Activated stellate cells are responsible for the deposition of extracellular matrix, increase the production of angiogenic factors and stimulate the recruitment of macrophages. The increase of angiogenic factors(which are secreted by macrophages, tumor cells and activated stellate cells) will induce the formation of new blood vessels, thereby supplying the tumor with more oxygen and nutrients, thus supporting tumor growth and offering a passageway in the circulatory system. In addition, the secretion of chemokines by the tumor cells leads to the recruitment of tumor associated macrophages. These tumor associated macrophages are key actors of cancer-related inflammation, being the main type of inflammatory cells infiltrating the tumor environment and exerting a tumor promoting effect by secreting growth factors, stimulating angiogenesis and influ-encing the activation of stellate cells. This complex interplay between the several cell types involved in liver cancer emphasizes the need for targeting the tumor stroma in HCC patients.