Angiogenesis and mast cells in non-Hodgkin's lymphoma: a strong correlation in angioimmunoblastic T-cell lymphoma

Steering Mast Cells or Their Mediators as a Prospective Novel Therapeutic Approach for the Treatment of Hematological Malignancies

Tumor cells require signaling and close interaction with their microenvironment for their survival and proliferation. In the recent years, Mast cells have earned a greater importance for their presence and role in cancers. It is known that mast cells are attracted towards tumor microenvironment by secreted soluble chemotactic factors. Mast cells seem to exert a pro-tumorigenic role in hematological malignancies with a few exceptions where they showed anti-cancerous role. This dual role of mast cells in tumor growth and survival may be dependent on the intrinsic characteristics of the particular tumor, differences in tumor microenvironment according to tumor type, and the interactions and heterogeneity of mediators released by mast cells in the tumor microenvironment. In many studies, Mast cells and their mediators have been shown to affect tumor survival and growth, prognosis, inflammation, tumor vascularization and angiogenesis. Modulating mast cell accumulation, viability, activity and mediator release patterns may thus be important in controlling these malignancies. In this review, we emphasize on the role of mast cells in lymphoid malignancies and discuss strategies for targeting and steering mast cells or their mediators as a potential therapeutic approach for the treatment of these malignancies.

Adipocytes, mast cells and angiogenesis

Healthy adipose tissue contains a wide variety of innate and adaptive immune cells, including macrophages, dendritic cells, mast cells, eosinophils, neutrophils, and lymphocytes. Numerous signaling molecules in the adipose microenvironment can positively or negatively modulate angiogenic processes, regulate the interaction between the vascular system and adipocytes, and participate in tumor progression. Mast cells are involved in the new formation or metabolism of fat, are present in abundant quantities in fatty tissue, among fat cells, and a number of mediators released from mast cells play a role in adipogenesis. Moreover, mast cells produce several pro-angiogenic factors and are involved in tumor angiogenesis. In this context, the angiogenic effect might be amplified when the adipocytes and mast cells act in concert, and treatment of adipose tissue- and mast cell-associated cancers with anti-angiogenic drugs may represent an alternative or adjuvant strategy for the treatment of these tumors.

Lymphomas and Their Microenvironment: A Multifaceted Relationship

It has become evident that the microenvironment - lymphocytes, macrophages, fibroblasts as well as the extracellular matrix, cytokines, chemokines, and a plethora of other cells, structures and substances residing in the vicinity of tumor cells - plays an important part in the maintenance of cancer growth and survival. This is also relevant in lymphomas. In this review, we give an outline on the importance of the microenvironment for tumors in general and lymphomas in particular, by highlighting certain basic principles of tumor-microenvironment interaction. The relationship of lymphomas and their microenvironment is multifaceted: lymphoma cells need growth factors and cytokines derived from microenvironmental cells for their sustenance and growth. On the contrary, many lymphomas silence or at least deregulate the immune system to escape recognition and subsequent elimination by immune cells, while giving advantage to suppressive microenvironmental compounds such as M2 polarized macrophages, regulatory T-cells, mast cells, and immunosuppressive fibroblasts. We also give a detailed insight across different lymphoma types to show the variety of tumor-microenvironment interactions. Due to its tremendous importance, the microenvironment has also become a new target for oncologic therapy. The most important finding concerning lymphomas with a focus on immunomodulatory substances is also, therefore, highlighted.

Mast Cells and Angiogenesis in Human Plasma Cell Malignancies

Bone marrow angiogenesis plays an important role in the pathogenesis and progression of hematological malignancies. It is well known that tumor microenvironment promotes tumor angiogenesis, proliferation, invasion, and metastasis, and also mediates mechanisms of therapeutic resistance. An increased number of mast cells has been demonstrated in angiogenesis associated with hematological tumors. In this review we focused on the role of mast cells in angiogenesis in human plasma cell malignancies. In this context, mast cells might act as a new target for the adjuvant treatment of these tumors through the selective inhibition of angiogenesis, tissue remodeling and tumor-promoting molecules, permitting the secretion of cytotoxic cytokines and preventing mast cell-mediated immune suppression.

Mast cells as sources of cytokines, chemokines, and growth factors

Mast cells are hematopoietic cells that reside in virtually all vascularized tissues and that represent potential sources of a wide variety of biologically active secreted products, including diverse cytokines and growth factors. There is strong evidence for important non-redundant roles of mast cells in many types of innate or adaptive immune responses, including making important contributions to immediate and chronic IgE-associated allergic disorders and enhancing host resistance to certain venoms and parasites. However, mast cells have been proposed to influence many other biological processes, including responses to bacteria and virus, angiogenesis, wound healing, fibrosis, autoimmune and metabolic disorders, and cancer. The potential functions of mast cells in many of these settings is thought to reflect their ability to secrete, upon appropriate activation by a range of immune or non-immune stimuli, a broad spectrum of cytokines (including many chemokines) and growth factors, with potential autocrine, paracrine, local, and systemic effects. In this review, we summarize the evidence indicating which cytokines and growth factors can be produced by various populations of rodent and human mast cells in response to particular immune or non-immune stimuli, and comment on the proven or potential roles of such mast cell products in health and disease.

Review of the biologic and clinical significance of genetic mutations in angioimmunoblastic T-cell lymphoma

Angioimmunoblastic T-cell lymphoma (AITL) is an age-related malignant lymphoma, characterized by immune system-dysregulated symptoms. Recent sequencing studies have clarified the recurrent mutations in ras homology family member A (RHOA) and in genes encoding epigenetic regulators, tet methyl cytosine dioxygenase 2 (TET2), DNA methyl transferase 3 alpha (DNMT3A) and isocitrate dehydrogenase 2, mitochondrial (IDH2), as well as those related to the T-cell receptor signaling pathway in AITL. In this review, we focus on how this genetic information has changed the understanding of the developmental process of AITL and will in future lead to individualized therapies for AITL patients.

Assessment of Angiogenesis in Children with Acute Lymphoblastic Leukemia Based on Serum Vascular Endothelial Growth Factor Assay

Introduction

Vascular endothelial growth factor A (VEGFA) is a key proangiogenic cytokine. The role of angiogenesis in acute lymphoblastic leukemia (ALL) is still unclear. The purpose of the study was to assess angiogenesis in children with ALL based on serum VEGFA level determined at diagnosis and at remission with further participant subdivision into different risk groups.

Materials and Methods

Forty children, aged 3-12 years (mean age: 8 years) with newly diagnosed ALL, were enrolled in the study. The control group (Group C) was twenty healthy children. According to the risk assessment, they were classified into a standard-risk group, an intermediate-risk group (IRG), or a high-risk group (HRG).

Results

The median serum VEGFA levels at diagnosis were significantly higher in IRG and HRG as compared to Group C. The VEGFA levels at remission were significantly higher in all study groups, as compared to Group C. The differences in median values of serum VEGFA levels between the study groups both at diagnosis and at remission were not statistically significant.

Conclusions

The angiogenesis in ALL seems to be intensified at diagnosis as a result of neoplasmatic bone marrow rebuilding and at remission as its intensive recovering.

Mast cells in lymphomas

Tumor microenvironment is involved in the pathogenesis and progression of human lymphomas. The lymphoma microenvironment is composed by stromal cells, immune cells (macrophages, plasma cells, mast cells, eosinophils, basophils, T- and B-cells), blood vessels and extracellular matrix proteins. This article is focused on the role of mast cells in lymphoma progression and angiogenesis. Mast cells might be regarded in a future perspective as a new target for the adjuvant treatment of tumors, including lymphomas.

Non-random spatial relationships between mast cells and microvessels in human endometrial carcinoma

Mast cells (MCs) accumulate in the stroma surrounding tumors, where they secrete angiogenic cytokines and proteases, and an increased number of MCs have been demonstrated in angiogenesis associated with solid and hematological tumors. The aim of this study is to contribute to the knowledge of distribution of MCs in tumors, investigating the pattern of distribution of tryptase-positive MCs around the blood vessels in human endometrial carcinoma samples by introducing a quantitative approach to characterize their spatial distribution. The results have shown that in human endometrial cancer bioptic specimens the spatial distribution of MCs shows significant deviation from randomness as compared with control group in which, instead, the spatial distribution of MCs is consistent with a random distribution. These findings confirm that MCs enhance tumor angiogenesis and their preferential localization along blood vessels and sites of new vessel formation sustaining the suggestion for an association between MCs and angiogenesis. However, this spatial association between vessels and MCs might simply reflect migrating MCs from the blood stream at vessel growing sites.

The impact of the immune system on tumor: angiogenesis and vascular remodeling

Angiogenesis, the formation of new blood vessels, as well as inflammation with massive infiltration of leukocytes are hallmarks of various tumor entities. Various epidemiological, clinical, and experimental studies have not only demonstrated a link between chronic inflammation and cancer onset but also shown that immune cells from the bone marrow such as tumor-infiltrating macrophages significantly influence tumor progression. Tumor angiogenesis is critical for tumor development as tumors have to establish a blood supply in order to progress. Although tumor cells were first believed to fuel tumor angiogenesis, numerous studies have shown that the tumor microenvironment and infiltrating immune cell subsets are important for regulating the process of tumor angiogenesis. These infiltrates involve the adaptive immune system including several types of lymphocytes as well as cells of the innate immunity such as macrophages, neutrophils, eosinophils, mast cells, dendritic cells, and natural killer cells. Besides their known immune function, these cells are now recognized for their crucial role in regulating the formation and the remodeling of blood vessels in the tumor. In this review, we will discuss for each cell type the mechanisms that regulate the vascular phenotype and its impact on tumor growth and metastasis.

The role of inflammatory cells in angiogenesis in multiple myeloma

Both innate and adaptive immune cells are involved in the mechanisms of endothelial cell proliferation, migration and activation, via production and release of a large spectrum of pro-angiogenic mediators, thus creating the specific microenvironment that favors increased rate of tissue vascularization. In this article, we focus on the immune cell component of the angiogenic process occurring during multiple myeloma progression. We also provide information on some anti-angiogenic properties of immune cells that may be applied for a potential pharmacological use as anti-angiogenic agents in the disease treatment.

The microenvironment in T-cell lymphomas: emerging themes

Peripheral T-cell lymphomas (PTCLs) are heterogeneous and uncommon malignancies characterized by an aggressive clinical course and a mostly poor outcome with current treatment strategies. Despite novel insights into their pathobiology provided by recent genome-wide molecular studies, several entities remain poorly characterized. In addition to the neoplastic cell population, PTCLs have a microenvironment component, composed of non-tumor cells and stroma, which is quantitatively and qualitatively variable, and which may have an effect on their pathological and clinical features. The best example is provided by angioimmunoblastic T-cell lymphoma (AITL), a designation reflecting the typical vascularization and reactive immunoblastic content of the tumor tissues. In this disease, a complex network of interactions between the lymphoma cells and the microenvironment exists, presumably mediated by the neoplastic T cells with follicular helper T-cell properties. A better understanding of the crosstalk between neoplastic T or NK cells and their microenvironment may have important implications for guiding the development of novel therapies.

Mast cells and macrophages exert beneficial and detrimental effects on tumor progression and angiogenesis

Mast cells and macrophages are critical regulators of inflammation and immunological response in the tumor microenvironment. Increased number of mast cells and macrophages have been reported to correlate with poor prognosis in numerous solid and hematological tumors. In contrast to their pro-tumorigenic role, mast cells and macrophages have shown also anti-tumorigenic effect in certain malignancies, for example by supporting cancer rejection. Thus, mast cells and macrophages can exert both detrimental and beneficial effects on tumor progression. Mast cell- and macrophages-derived growth factors able to promote tumor development and angiogenesis include TNF-α, TGF-β1, FGF-2, VEGF, PDGF, IL-8, osteopontin, and NGF. On the contrary, mast cell- and macrophages-produced cytokines that may participate in anti-tumor response include IL-1, IL-2, IL-4, IL-10, and IFN-γ. It is to note that mast cells and macrophages may also show beneficial and detrimental effects in the same cancer depending on the tumor stage.

Mast cells, angiogenesis and cancer

Mast cells (MCs) were first described by Paul Ehrlich 1 in his doctoral thesis. MCs have long been implicated in the pathogenesis of allergic reactions and certain protective responses to parasites. As most tumors contain inflammatory cell infiltrates, which often include plentiful MCs, the question as to the possible contribution of MCs to tumor development has progressively been emerging. In this chapter, the specific involvement of MCs in tumor biology and tumor fate will be considered, with particular emphasis on the capacity of these cells to stimulate tumor growth by promoting angiogenesis and lymphangiogenesis. Data from experimental carcinogenesis and from different tumor settings in human pathology will be summarized. Information to be presented will suggest that MCs may serve as a novel therapeutic target for cancer treatment.

Mast cells, angiogenesis, and tumour growth

Accumulation of mast cells (MCs) in tumours was described by Ehrlich in his doctoral thesis. Since this early account, ample evidence has been provided highlighting participation of MCs to the inflammatory reaction that occurs in many clinical and experimental tumour settings. MCs are bone marrow-derived tissue-homing leukocytes that are endowed with a panoply of releasable mediators and surface receptors. These cells actively take part to innate and acquired immune reactions as well as to a series of fundamental functions such as angiogenesis, tissue repair, and tissue remodelling. The involvement of MCs in tumour development is debated. Although some evidence suggests that MCs can promote tumourigenesis and tumour progression, there are some clinical sets as well as experimental tumour models in which MCs seem to have functions that favour the host. One of the major issues linking MCs to cancer is the ability of these cells to release potent pro-angiogenic factors. This review will focus on the most recent acquisitions about this intriguing field of research. This article is part of a Special Issue entitled: Mast cells in inflammation.

Proangiogenic cytokines vascular-endothelial growth factor and basic fibroblst growth factor in childhood lymphadenopathy

Increased angiogenesis is observed both in the inflammatory and in the neoplasmatic tissue. The aim of the study was to assess the diagnostic significance of serum concentration of vascular-endothelial growth factor (sVEGF) and basic fibroblast growth factor (sbFGF) in the various forms of lymphadenopathy in children. Ninety-four children with lymphadenopathy were studied: group A, 52 patients with lymphadenitis; group B, 42 patients with lymphomas. Group B was divided into subgroups: B(P), children with lymphomas in peripheral lymph nodes and B(M), children with lymphomas in peripheral lymph nodes and mediastinal tumor. The healthy control group was 20 children. Using enzyme-linked immunosorbent assays the authors quantified VEGF and bFGF in serum of healthy children and of children with lymphadenopathy. The sVEGF in group A was significantly higher than controls (313.8 versus 44.6 pg/mL; P <.05) and in group B was 633.4 pg/mL and was significantly higher than controls (P <.0001). The sVEGF and bFGF in group A versus subgroup B(P) were significantly lower (P(VEGF) <.05, P(bFGF) <.05), and sVEGF in subgroup B(P) versus B(M) was significantly lower (P <.05). These results show that the evaluation of serum VEGF concentration might be useful as noninvasive diagnosis of some chronic peripheral lymphadenopathies in children.

Angiogenesis in non-Hodgkin's lymphoma: Clinico-pathological correlations and prognostic significance in specific subtypes

The aim of the study was to evaluate angiogenesis in different subtypes of non-Hodgkin's lymphoma (NHL) and to correlate angiogenic scores to clinical endpoints. Pre-therapeutic lymph node biopsies from 308 patients with NHL [107 follicular B-cell lymphoma (FL), 94 diffuse large B-cell lymphoma (DLBCL), 107 peripheral T-cell lymphoma (PTCL)] were studied. Microvessels were scored according to the Chalkley and microvessel density method (MVD) methods. Vascular endothelial growth factor (VEGF) protein expression was evaluated by immunohistochemistry. Both Chalkley and MVD methods showed, that the lymphoma subtypes differed significantly in angiogenic scores (P < 0.001). Angiogenic scores in tumor area were highest in PTCL, and lowest in FL. However, a remarkable high microvessel density was found in interfollicular areas of FL. In FL, high interfollicular MVD scores predicted progressive disease and poorer overall and event-free survival (P = 0.024 and 0.013). High interfollicular Chalkley scores correlated with transformation to DLBCL (P = 0.01). VEGF expression was detected in all NHL subtype, and the strongest expression was found in PTCL. In FL, patients with diffuse VEGF expression in lymphoma cells had poorer overall survival than those with focal expression.

Immune cells and angiogenesis

Both innate and adaptive immune cells are involved in the mechanisms of endothelial cell proliferation, migration and activation, through the production and release of a large spectrum of pro-angiogenic mediators. These may create the specific microenvironment that favours an increased rate of tissue vascularization. In this review, we will focus on the immune cell component of the angiogenic process in inflammation and tumour growth. As angiogenesis is the result of a net balance between the activities exerted by positive and negative regulators, we will also provide information on some antiangiogenic properties of immune cells that may be utilized for a potential pharmacological use as antiangiogenic agents in inflammation as well as in cancer.

The controversial role of mast cells in tumor growth

Mast cells (MCs) were first described by Paul Ehrlich (Beiträge zur Theorie und Praxis der Histologischen Färbung, Thesis, Leipzig University, 1878). They have long been implicated in the pathogenesis of allergic reactions and protective responses to parasites. However, their functional role has been found to be complex and multifarious. MCs are also involved in various cell-mediated immune reactions and found in tissues from multiple disease sites, and as a component of the host reaction to bacteria, parasite, and even virus infections. They also participate in angiogenic and tissue repair processes after injury. The importance of a possible functional link between chronic inflammation and cancer has long been recognized. As most tumors contain inflammatory cell infiltrates, which often include plentiful MCs, a possible contribution of these cells to tumor development has emerged. In this review, general biology of mast cells, their development, anatomical distribution, and phenotype as well as their secretory products will first be discussed. The specific involvement of MCs in tumor biology and tumor fate will then be considered, with particular emphasis on their capacity to stimulate tumor growth by promoting angiogenesis and lymphangiogenesis. Finally, it is suggested that mast cells may serve as a novel therapeutic target for cancer treatment.

Mast cells in diffuse large B-cell lymphoma; their role in fibrosis

AIMS

Mast cells (MCs) are associated with fibrosis in various diseases. MCs comprise two phenotypes: the MC(TC) phenotype contains tryptase and chymase, whereas the MC(T) phenotype contains tryptase. Interleukin (IL)-4 promotes the development of MC(TC) from the MC(T) phenotype. The aim of this study was to determine the relationship between MC phenotypes and fibrosis in diffuse large B-cell lymphoma (DLBCL).

METHODS AND RESULTS

We examined the distribution and density of MCs in 50 DLBCL and 20 reactive lymph nodes, and evaluated MC phenotypes and IL-4-expressing cells. To detect MCs, immunohistochemistry for tryptase and chymase was performed. The 50 DLBCLs were histologically divided into three groups: no fibrosis (32 cases), reticular type (eight cases) showing reticular fibrosis, and bundle type (10 cases) showing collagenous bundles. The density of tryptase-positive MCs was higher than that of chymase-positive MCs. The densities of tryptase-positive and chymase-positive MCs in fibrotic areas were significantly higher than those in the cellular areas in the reticular and bundle groups. Double immunostaining revealed that MCs in DLBCL comprised MC(T) and MC(TC) phenotypes. Chymase-positive MCs and T lymphocytes expressed IL-4. Although there were few chymase-positive MCs in reactive lymph nodes, the density of tryptase-positive MCs was not different from that in the 'no fibrosis' group.

CONCLUSIONS

Tryptase-positive and chymase-positive MCs are associated with fibrosis in DLBCL.

Mast cell contribution to angiogenesis related to tumour progression

The current wisdom is that tumours are endowed with an angiogenic capability and that their growth, invasion and metastasis are angiogenesis dependent. It is now well documented that neoplastic cells are influenced by their microenvironment and vice versa. The specific organ microenvironment determines the extent of cancer cell proliferation, angiogenesis, invasion and survival. Tumour cells are surrounded by an infiltrate of inflammatory cells, namely lymphocytes, neutrophils, macrophages and mast cells (MCs), which communicate via a complex network of intercellular signalling pathways, mediated by surface adhesion molecules, cytokines and their receptors. This review article summarizes: (i) the MC mediators involved in angiogenesis; (ii) the experimental evidence concerning the role played by MCs in angiogenesis; (iii) the list of solid and haematological tumours in which a close relationship between angiogenesis, tumour progression and MCs has been demonstrated; (iv) the circumstances in which MCs are a critical source of angiogenic factors in vivo, and in such cases, the signals that regulate their production and secretion that need to be determined as a prelude to the elaboration of new therapeutic strategies associated with MC presence and activation.

Hematopoietic Cancer and Angiogenesis

The growth of solid tumors is certainly angiogenesis dependent. However, the role of angiogenesis in the growth and survival of leukemias and other hematological malignancies has only been rendered evident since 1994 in a series of demonstrations showing that the progression of several forms is clearly related to their degree of angiogenesis. Here, we present an overview of the literature concerning the relationship between angiogenesis and disease progression in several hematological malignancies and the recent advances in antiangiogenesis in these diseases and we describe the most important active substances, preclinical and clinical data, and future perspectives.

Mast cells degranulation affects angiogenesis in the rat uterine cervix during pregnancy

During pregnancy, it is essential that sufficient nutrients are supplied by the vascular system to support the dramatic modifications of the rat uterine cervix. Angiogenesis refers to the growth of new blood vessels from pre-existing microcirculation and mast cells have been associated with this process. This study examined the modifications of the vascular compartment and the distribution of mast cells on cervical tissue during pregnancy. Using disodium cromoglycate as a mast cell stabilizer, we determined the effects of the mast cell degranulation on cervical angiogenesis. Mast cell distribution and their degranulation status were evaluated by immunohistochemistry. Endothelial cell proliferation was measured by bromodeoxyuridine incorporation. Vascular areas (absolute and relative) and maturation indices were assessed by quantitative immunohistochemistry of von Willebrand factor and alpha-smooth muscle actin respectively. Mast cells were predominantly observed during the first half of pregnancy in the perivascular zones. The values of bromodeoxyuridine incorporation, absolute vascular area and vascular maturation index exhibited a significant increase throughout pregnancy. All animals that received mast cell stabilizer showed more than 40% of non-degranulated mast cells. Treated rats exhibited a decrease in endothelial proliferation and in relative vascular area; in addition, a large proportion of mature blood vessels was observed, suggesting a diminished level of new vessel formation. The effects of the mast cell stabilizer were sustained beyond the end of treatment. This is the first report that brings evidence that mast cell degranulation could be a necessary process to contribute to the normal angiogenesis of the rat cervix during pregnancy. Further investigations are needed to elucidate the possible implications of abnormal vascular development of the uterine cervix on the physiological process of ripening and parturition.

Effect of mast cell in pathogenesis of gastric eosinophilic granuloma

AIM

To investigate the function of mast cells in the pathogenesis of gastric eosinophilic granuloma.

METHODS

Paraffin embedded tissue sections from 23 gastric eosinophilic granuloma patients and 15 gastric ulcer patients were stained with anti-human mast cell tryptase to count the mast cells and degranulated mast cells. Anti-human CD34 antibody was used to detect the mocrovessel density with immunohistochemical technique. Mast cell degranulation was also studied by electron microscope.

RESULTS

The quantity of mast cells in gastric eosinophilic granuloma was similar to that in gastric ulcer(9.1±3.0 vs 8.9±3.0, P>0.05). The quantity and ratio of degranulated mast cells were significantly greater in gastric eosinophilic granuloma patients than in gastric ulcer control subjects(7.3±2.4 vs 4.3±1.4, 80.3±15.7% vs 48.4±15.7%, P<0.01). Microvessel density was higher in the patients of high mast cell count than in patients of low mast cell count (57.3±10.7 vs 32.4±7.2, P<0.01). There was a positive relevance between the amount of mast cells and eosinophils (r = 0.931, P<0.01).

CONCLUSION

Mast cells are important cells in the pathogenesis of gastric eosinophilic granuloma.

Mast cells and human hepatocellular carcinoma

AIM: To investigate the density of mast cells (MCs) in human hepatocellular carcinoma (HCC), and to determine whether the MCs density has any correlations with histopathological grading, staging or some baseline patient characteristics.

METHODS: Tissue sections of 22 primary HCCs were histochemically stained with toluidine blue, in order to be able to quantify the MCs in and around the neoplasm using a computer-assisted image analysis system. HCC was staged and graded by two independent pathologists. To identify the sinusoidal capillarisation of each specimen 3 μm thick sections were histochemically stained with sirius red, and semi-quantitatively evaluated by two independent observers. The data were statistically analysed using Spearman's correlation and Student's t-test when appropriate.

RESULTS: MCs density did not correlate with the age or sex of the patients, the serum alanine aminotransferase (ALT) or aspartate aminotransferase (AST) levels, or the stage or grade of the HCC. No significant differences were found between the MCs density of the patients with and without hepatitis C virus infection, but they were significantly higher in the specimens showing marked sinusoidal capillarisation.

CONCLUSION: The lack of any significant correlation between MCs density and the stage or grade of the neoplastic lesions suggests that there is no causal relationship between MCs recruitment and HCC. However, as capillarisation proceeds concurrently with arterial blood supply during hepatocarcinogenesis, MCs may be considered of primary importance in the transition from sinusoidal to capillary-type endothelial cells and the HCC growth.

Angiogenesis in hematologic malignancies

Angiogenesis is defined as the formation of new capillaries from preexisting blood vessels and plays an important role in the progression of solid tumors. Recently a similar relationship has been described in several hematologic malignancies. Expression of the angiogenic peptides vascular endothelial growth factor (VEGF) and basic fibroblast growth factor correlates with clinical characteristics in leukemia and non-Hodgkin's-lymphoma and the serum/plasma concentrations serve as predictors of poor prognosis. Increased bone marrow microvessels in multiple myeloma (MM) are correlated with decreased overall survival. Thalidomide which has antiangiogenic effects and direct cytotoxic effects was found to be effective in MM, myelodysplastic syndrome and acute myeloid leukemia (AML). Preliminary data indicate activity of VEGF-tyrosine kinase inhibitors in AML. Clinical research is now aimed at testing antiangiogenic treatment strategies in several hematologic neoplasms as well as identifying the best candidate patients for specific approaches.

Angiogenesis and anti-angiogenesis in hematological malignancies

Although it is well established that the growth of solid tumors requires vigorous neovascularization, it has been assumed that leukemias and other hematological malignancies do not depend on angiogenesis. However, the role of angiogenesis in growth and survival of neoplastic cells of the hematopoietic system has recently been recognized, and provides a rationale for novel therapeutic approaches to hematological malignancy. This review summarizes the literature concerning the relationship between angiogenesis and disease progression of several hematological malignancies. It is becoming increasingly evident that agents that interfere with blood vessel formation also block tumor progression, and, accordingly, antiangiogenic therapy has gained much interest as a potential adjunct to conventional therapy of many hematological malignancies. Recent successful applications of antiangiogenic agents that interfere or block the progression of hematological malignancies are evaluated in light of recent demonstrations of potent angiogenic activity of several hematopoietic growth factors. A novel finding regarding the role of angiogenesis in hematological malignancies, which accounts for many clinical observations as well as the apparent independence of these tumors on marrow vascularity, is presented. The information presented in this review will facilitate the design of future clinical trials using antiangiogenic agents for the treatment of hematological malignancies and will provide a basis for the design of experiments undertaken to define the mechanisms involved, mechanisms that may shed new light on the pathology of hematological malignancies.

Mast cells and angiogenesis

Angiogenesis is tightly regulated by pro- and anti-angiogenic factors. Secreting mast cells are able to induce and enhance angiogenesis via multiple in part interacting pathways. They include mast cell-derived (i) potent pro-angiogenic factors such as VEGF, bFGF, TGF-beta, TNF-alpha and IL-8, (ii) proteinases and heparin, that release heparin-binding pro-angiogenic factors lodged on cell surfaces and in the extracellular matrix (ECM), (iii) histamine, VEGF, and certain lipid-derived mediators that induce microvascular hyperpermeability having pro-angiogenic effects, (iv) chemotactic recruitment of monocytes/macrophages and lymphocytes that are able to contribute with angiogenesis-modulating molecules, (v) activation of platelets that release pro-angiogenic factors, (vi) activation of neighboring stationary non-mast cells, which secrete pro-angiogenic factors, ECM-degrading proteinases and stem cell factor which attracts, mitogenically stimulates and activates mast cells, (vii) auto- and paracrine stimulation of mast cells by stem cell factor, (viii) recruitment of mast cells by pro-angiogenic factors such as VEGF, bFGF and TGF-beta. As a result of ECM-degradation and changes in the microenvironment following initial mast cell secretion, the mast cell populations may change significantly in number, phenotype and function. In tumor models, mast cells have been shown to play a decisive role in inducing the angiogenic switch which precedes malignant transformation. There is, moreover, strong evidence that mast cells significantly influence angiogenesis and thus growth and progression in human cancers.