Angiogenesis extent and macrophage density increase simultaneously with pathological progression in B-cell non-Hodgkin's lymphomas

Histopathological Evaluation of Angiogenic Markers in Non-Hodgkin's Lymphoma

Background Angiogenesis plays a key role in the development, maintenance, and progression of tumor. The incidence of non-Hodgkin's lymphoma (NHL) is increasing from the past three decades.

Materials and Methods The aim of the study is to evaluate microvessel density (MVD) using CD34 monoclonal antibody and vascular endothelial growth factor (VEGF) using monoclonal antibody that were studied in pretreatment paraffin-embedded tissue samples of 60 cases.

Results MVD was found to be increased in parallel with increasing grade of tumor. B-NHL had a mean MVD of 79.5 ± 8.8 (no./mm2), while T-NHL had a mean MVD of 183 ± 37.6 (no./mm2). VEGF expression was seen in 42 cases (70%), 20 cases (33.3%) showed strong VEGF expression, and the remainder showed either weak (36.6%) or no (30%) staining. Strong VEGF expression is seen in 100% cases of T-NHL and 77.7% cases of B-NHL. Mean MVD and VEGF expression was found to be correlated significantly with the histological grade of NHL (p = 0.001 and p = 0.000, respectively). Average microvessel counts were 53, 82.9, and 130.8 vessels (no./mm2) for negative, weak, and strong VEGF staining, respectively. These differences were statistically significant (p = 0.005 for strong vs. negative and p = 0.091 for strong vs. weak VEGF staining individually).

Conclusion As the grade of tumor progresses, the angiogenic potential also advances which seems to depend on VEGF. The presence of higher MVD in high-grade lymphomas can be utilized for antiangiogenic drugs.

Prognostic Value of Microvessel Density in Non-Hodgkin Lymphoma: A Meta-Analysis

BACKGROUND

Angiogenesis in non-Hodgkin lymphoma (NHL) has been investigated by a variety of studies. However, the correlation between angiogenesis and the occurrence or prognosis of NHL patients remains controversial.

METHODS

We performed a systematic and comprehensive retrieval of relevant literatures from PubMed, EMBASE, and Web of Science databases. The quality of the eligible studies was assessed using the Newcastle-Ottawa Scale (NOS).

RESULTS

Fifteen eligible studies containing a total of 1373 NHL patients were included in this study. All the eligible studies were high-quality studies scoring ≥6 points. MVD was not different between NHL and control (SMD = 0.281, 95% CI: -1.410 to 1.972, p = 0.745). High MVD was associated with advanced disease stage (OR = 1.580, 95% CI: 1.080-2.311, p = 0.018) and unfavorable OS (HR = 1.656, 95% CI: 1.366-2.009, p = 0.000) but not with PFS (HR = 1.349, 95% CI: 0.852-2.136, p = 0.201).

CONCLUSION

This meta-analysis demonstrated that high MVD was related to advanced disease stage and associated with unfavorable OS of NHL patients.

Angiogenesis in Lymph Nodes Is a Critical Regulator of Immune Response and Lymphoma Growth

Tumor-induced remodeling of the microenvironment in lymph nodes (LNs) includes the formation of blood vessels, which goes beyond the regulation of metabolism, and shaping a survival niche for tumor cells. In contrast to solid tumors, which primarily rely on neo-angiogenesis, hematopoietic malignancies usually grow within pre-vascularized autochthonous niches in secondary lymphatic organs or the bone marrow. The mechanisms of vascular remodeling in expanding LNs during infection-induced responses have been studied in more detail; in contrast, insights into the conditions of lymphoma growth and lodging remain enigmatic. Based on previous murine studies and clinical trials in human, we conclude that there is not a universal LN-specific angiogenic program applicable. Instead, signaling pathways that are tightly connected to autochthonous and infiltrating cell types contribute variably to LN vascular expansion. Inflammation related angiogenesis within LNs relies on dendritic cell derived pro-inflammatory cytokines stimulating vascular endothelial growth factor-A (VEGF-A) expression in fibroblastic reticular cells, which in turn triggers vessel growth. In high-grade B cell lymphoma, angiogenesis correlates with poor prognosis. Lymphoma cells immigrate and grow in LNs and provide pro-angiogenic growth factors themselves. In contrast to infectious stimuli that impact on LN vasculature, they do not trigger the typical inflammatory and hypoxia-related stroma-remodeling cascade. Blood vessels in LNs are unique in selective recruitment of lymphocytes via high endothelial venules (HEVs). The dissemination routes of neoplastic lymphocytes are usually disease stage dependent. Early seeding via the blood stream requires the expression of the homeostatic chemokine receptor CCR7 and of L-selectin, both cooperate to facilitate transmigration of tumor and also of protective tumor-reactive lymphocytes via HEV structures. In this view, the HEV route is not only relevant for lymphoma cell homing, but also for a continuous immunosurveillance. We envision that HEV functional and structural alterations during lymphomagenesis are not only key to vascular remodeling, but also impact on tumor cell accessibility when targeted by T cell-mediated immunotherapies.

Bevacizumab synergises with the BCL 2 inhibitor venetoclax to effectively treat B-cell non-Hodgkin's lymphoma

OBJECTIVES

Our present study has shown a potential role for VEGF-A-mediated autocrine signalling to promote survival and proliferation of SU-DHL-6 cells, but the cells could not undergo apoptosis but rather decrease proliferation after bevacizumab treatment. Therefore, we would like to further study the antitumour efficacy of venetoclax (BCL2 inhibitor) in combination with bevacizumab in B-cell NHL.

METHODS

The human cytokine antibody array, RT-qPCR, Western blot, ELISA, apoptosis assay and xenografted mouse model et al were used.

RESULTS

We described a unique phenomenon that SU-DHL-6 cells showed cell density-dependent survival and growth. Then, we suggested the expression of VEGF-A was positively correlated with the cell density using a human cytokine antibody array and indicated an important role of VEGF-A in the survival and proliferation of SU-DHL-6 cells. Additionally, xenografted SU-DHL-6 cells formed tumours in mice that grew in response to VEGF stimulation. GEO data set also suggested that high VEGF-A expression reflected poor prognosis. The combination therapy with bevacizumab and navitoclax could significantly induce of cell death in vitro and reduce the tumour size and weight with well tolerated in vivo.

CONCLUSIONS

Our findings propose a novel combined strategy in which bevacizumab synergises with the BCL2 inhibitor venetoclax that is effective against B-cell NHL.

Angiogenic Molecules in Hodgkin's Disease: Results from Sequential Serum Analysis

Increased angiogenic activity has been demonstrated in lymphoproliferative diseases including Hodgkin's disease. In the current study, the levels of circulating angiogenic molecules in 60 Hodgkin's patients were determined prior to and after treatment and correlated to disease stage and prognostic score. Hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGF), interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were increased in Hodgkin's patients in comparison to healthy controls (p<0.001). Angiogenin and angiopoietin-2 levels did not differ from controls. HGF, VEGF, TNF-α and angiogenin decreased significantly in Hodgkin's patients after standard treatment (p<0.001 for HGF, p<0.05 for VEGF, TNF-α and angiogenin). Furthermore, HGF and TNF-α increased with advancing stage of disease (p<0.05). HGF and VEGF correlated significantly with IL-6 (r=0.56, p<0.0005 and r=0.57, p<0.001 respectively). In conclusion, Hodgkin's disease displays an angiogenic activity as depicted by the increased serum levels of a number of angiogenic cytokines. HGF seems to be the prominent molecule in Hodgkin's disease, which may be used to monitor the disease status and the response to treatment.

Differentiation of Diffuse Large B-cell Lymphoma From Follicular Lymphoma Using Texture Analysis on Conventional MR Images at 3.0 Tesla

RATIONAL AND OBJECTIVES

Diffuse large B-cell lymphoma (DLBCL) represents the most common type of aggressive non-Hodgkin lymphoma (NHL); follicular lymphoma (FL) is the most frequent indolent NHL. The aim of this study was to investigate whether texture-based analysis of conventional magnetic resonance imaging (MRI) allows discrimination of DLBCL from FL, and further, to correlate the MRI texture features with diffusion-weighted imaging apparent diffusion coefficient (ADC) value and tumor tissue cellularity.

MATERIALS AND METHODS

Forty-one patients with histologically proven NHL (30 DLBCL and 11 FL) underwent conventional MRI and diffusion-weighted imaging examination before treatment. Based on regions of interest, texture analysis was performed on T1-weighted images pre- and postcontrast enhancement and on T2-weighted images with and without fat suppression, and features derived from the run-length matrix- and co-occurrence matrix-based methods were analyzed. Receiver operating characteristic curves were performed for the three most discriminative texture features for the differentiation of the two most common types of lymphoma. The analyzed MRI texture features were correlated with the ADC value and the tumor tissue cellularity.

RESULTS

We found that on T1-weighted images postcontrast enhancement, run-length matrix-based texture analysis for lesion classification differentiated DLBCL from FL, with specificity and sensitivity of 76.6% and 76.5%, respectively. There was no correlation between the texture features and the ADC value or tumor tissue cellularity.

CONCLUSIONS

DLBCL and FL can be differentiated by means of texture analysis on T1-weighted MRI postcontrast enhancement. These results could serve as a basis for the use of the texture features on conventional MRI as adjunct to clinical examination to distinguish DLBCL from FL.

Tumour-associated macrophages correlate with microvascular bed extension in colorectal cancer patients

Tumour‐associated macrophages (TAMs) represent pivotal components of tumour microenvironment promoting angiogenesis, tumour progression and invasion. In colorectal cancer (CRC), there are no conclusive data about the role of TAMs in angiogenesis‐mediated tumour progression. In this study, we aimed to evaluate a correlation between TAMs, TAM immunostained area (TAMIA) microvascular density (MVD), endothelial area (EA) and cancer cells positive to VEGF‐A (CCP‐VEGF‐A) in primary tumour tissue of locally advanced CRC patients undergone to radical surgery. A series of 76 patients with CRC were selected and evaluated by immunohistochemistry and image analysis. An anti‐CD68 antibody was employed to assess TAMs and TAMIA expression, an anti‐CD34 antibody was utilized to detect MVD and EA expression, whereas an anti‐VEGF‐A antibody was used to detect CCP‐VEGF‐A; then, tumour sections were evaluated by image analysis methods. The mean ± S.D. of TAMs, MVD and CCP‐VEGF‐A was 65.58 ± 21.14, 28.53 ± 7.75 and 63% ± 37%, respectively; the mean ± S.D. of TAMIA and EA was 438.37 ± 124.14μ² and 186.73 ± 67.22μ², respectively. A significant correlation was found between TAMs, TAMIA, MVD and EA each other (r ranging from 0.69 to 0.84; P ranging from 0.000 to 0.004). The high level of expression of TAMs and TAMIA in tumour tissue and the significant correlation with both MVD and EA illustrate that TAMs could represent a marker that plays an important role in promoting angiogenesis‐mediated CRC. In this context, novel agents killing TAMs might be evaluated in clinical trials as a new anti‐angiogenic approach.

The delicate balance of macrophages in colorectal cancer; their role in tumour development and therapeutic potential

Most tumours are heavily infiltrated by immune cells. This has been correlated with either a good or a bad patient prognosis, depending on the (sub) type of immune cells. Macrophages represent one of the most prominent leukocyte populations in the majority of tumours. Functions of macrophages range from cytotoxicity, to stimulation of tumour growth by secretion of cytokines, growth and angiogenic factors, or suppressing immune responses. In most tumours macrophages are described as cells with immune suppressing, and wound healing properties, which aids tumour development. Yet, increasing evidence shows that macrophages are potent inhibitors of tumour growth in colorectal cancer. Macrophages in this respect show high plasticity. The presence of high macrophage numbers in the tumour may therefore become advantageous, if cells can be reprogrammed from tumour promoting macrophages into potent effector cells. Enhancing cytotoxic properties of macrophages by microbial products, pro-inflammatory cytokines or monoclonal antibody therapy are promising possibilities, and are currently tested in clinical trials.

The potential of fibroblast growth factor/fibroblast growth factor receptor signaling as a therapeutic target in tumor angiogenesis

INTRODUCTION

Fibroblast growth factors (FGFs) are endowed with a potent pro-angiogenic activity. Activation of the FGF/FGF receptor (FGFR) system occurs in a variety of human tumors. This may lead to neovascularization, supporting tumor progression and metastatic dissemination. Thus, a compelling biologic rationale exists for the development of anti-FGF/FGFR agents for the inhibition of tumor angiogenesis in cancer therapy.

AREAS COVERED

A comprehensive search on PubMed was performed to identify studies on the role of the FGF/FGFR system in angiogenesis. Endothelial FGFR signaling, the pro-angiogenic function of canonical FGFs, and their role in human tumors are described. In addition, experimental approaches aimed at the identification and characterization of nonselective and selective FGF/FGFR inhibitors and their evaluation in clinical trials are summarized.

EXPERT OPINION

Different approaches can be envisaged to inhibit the FGF/FGFR system, a target for the development of 'two-compartment' anti-angiogenic/anti-tumor agents, including FGFR selective and nonselective small-molecule tyrosine kinase inhibitors, anti-FGFR antibodies, and FGF ligand traps. Further studies are required to define the correlation between tumor vascularization and activation of the FGF/FGFR system and for the identification of cancer patients more likely to benefit from anti-FGF/FGFR treatments. In addition, advantages and disadvantages about the use of selective versus non-selective FGF inhibitors remain to be elucidated.

Myeloid-derived suppressor cells: their role in the pathophysiology of hematologic malignancies and potential as therapeutic targets

Myeloid-derived suppressor cells (MDSCs) are a heterogeneous population of immature myeloid cells at various stages of differentiation/maturation that have a role in cancer induction and progression. They function as vasculogenic and immunosuppressive cells, utilizing multiple mechanisms to block both innate and adaptive anti-tumor immunity. Recently, their mechanism of action and clinical importance have been defined, and the cross-talk between myeloid cells and cancer cells has been shown to contribute to tumor induction, progression, metastasis and tolerance. In this review, we focus on the role of MDSCs in hematologic malignancies and the therapeutic approaches targeting MDSCs that are currently in clinical studies.

Role of tumor associated macrophages in tumor angiogenesis and lymphangiogenesis

Tumor angiogenesis is an essential process for supplying rapidly growing malignant tissues with essential nutrients and oxygen. An angiogenic switch allows tumor cells to survive and grow, and provides them access to vasculature resulting in metastatic disease. Monocyte-derived macrophages recruited and reprogrammed by tumor cells serve as a major source of angiogenic factors boosting the angiogenic switch. Tumor endothelium releases angiopoietin-2 and further facilitates recruitment of TIE2 receptor expressing monocytes (TEM) into tumor sites. Tumor-associated macrophages (TAM) sense hypoxia in avascular areas of tumors, and react by production of angiogenic factors such as VEGFA. VEGFA stimulates chemotaxis of endothelial cells (EC) and macrophages. In some tumors, TAM appeared to be a major source of MMP9. Elevated expression of MMP9 by TAM mediates extracellular matrix (ECM) degradation and the release of bioactive VEGFA. Other angiogenic factors released by TAM include basic fibroblast growth factor (bFGF), thymidine phosphorylase (TP), urokinase-type plasminogen activator (uPA), and adrenomedullin (ADM). The same factors used by macrophages for the induction of angiogenesis [like vascular endothelial growth factor A (VEGF-A) and MMP9] support lymphangiogenesis. TAM can express LYVE-1, one of the established markers of lymphatic endothelium. TAM support tumor lymphangiogenesis not only by secretion of pro-lymphangiogenic factors but also by trans-differentiation into lymphatic EC. New pro-angiogenic factor YKL-40 belongs to a family of mammalian chitinase-like proteins (CLP) that act as cytokines or growth factors. Human CLP family comprises YKL-40, YKL-39, and SI-CLP. Production of all three CLP in macrophages is antagonistically regulated by cytokines. It was recently established that YKL-40 induces angiogenesis in vitro and in animal tumor models. YKL-40-neutralizing monoclonal antibody blocks tumor angiogenesis and progression. The role of YKL-39 and SI-CLP in tumor angiogenesis and lymphangiogenesis remains to be investigated.

Critical signal transduction pathways in CLL

Receptor tyrosine kinases (RTKs) are cell-surface transmembrane receptors that contain regulated kinase activity within their cytoplasmic domain and play a critical role in signal transduction in both normal and malignant cells. Besides B cell receptor (BCR) signaling in chronic lymphocytic leukemia (CLL), multiple RTKs have been reported to be constitutively active in CLL B cells, resulting in enhanced survival and resistance to apoptosis of the leukemic cells induced by chemotherapeutic agents. In addition to increased plasma levels of various types of cytokines/growth factors in CLL, we and others have detected that CLL B cells spontaneously produce multiple cytokines in vitro which may constitute an autocrine loop of RTK activation on the leukemic B cells. Moreover, aberrant expression and activation of non-RTKs, for example, Src/Syk kinases, induce resistance of the leukemic B cells to therapy. Based on current available knowledge, we detailed the impact of aberrant activities of various RTKs/non-RTKs on CLL B cell survival and the potential of using these signaling components as future therapeutic targets in CLL therapy.

Rational design and synthesis of novel 2-(substituted-2H-chromen-3-yl)-5-aryl-1H-imidazole derivatives as an anti-angiogenesis and anti-cancer agent

Based on the earlier proven pharmacophore analogues of cancer a novel 2-(substituted-2H-chromen-3-yl)-5-aryl-1H-imidazoles were rationally designed, synthesized and used for competitive biological activity against cancer cell lines.

The role of angiogenesis in human non-Hodgkin lymphomas

The role of angiogenesis in the growth of lymphomas and survival of patients with leukemias and other hematological malignancies has become evident since 1994. Angiogenic factors, such as vascular endothelial growth factor and its receptors together with other tumor microenvironment components, including myelo-monocytic cell, mast cells, endothelial progenitor cells, and circulating endothelial cells, have been shown to be important in the progression and maintenance of lymphoproliferative disorders. In this review article, we present an overview of the literature focusing on the relationship between angiogenesis and disease progression and the recent advantages in the antiangiogenic treatment in human non-Hodgkin lymphomas.

Prognostic significance of immunohistochemical expression of the angiogenic molecules vascular endothelial growth factor-A, vascular endothelial growth factor receptor-1 and vascular endothelial growth factor receptor-2 in patients with classical Hodgkin lymphoma

Angiogenesis leads to new blood vessel formation and is implicated in both physiological and pathological situations. The vascular endothelial growth factor (VEGF) family is the major mediator of this process. The aim of our study was to evaluate the expression of VEGF-A, vascular endothelial growth factor receptor-1 (VEGFR-1) and VEGFR-2 and their correlation with clinicopathological parameters and prognosis in patients with classical Hodgkin lymphoma (cHL), since the role of angiogenesis in this tumor still remains unclear. The immunohistochemical expression of VEGF-A, VEGFR-1 and VEGFR-2 was examined in 194 patients with cHL. The neoplastic Hodgkin Reed-Sternberg (HRS) cells expressed VEGF-A, VEGFR-1 and VEGFR-2 in 90.3%, 97.2% and 94.1% of cases, respectively. Only the expression of VEGFR-2 was positively correlated with serum albumin levels ≥ 4 g/dL. No correlation with patient outcome was observed. All three molecules were statistically correlated with ramifications of blood vessels. Summarizing, our results are not sufficient to consider VEGF-A and/or VEGF receptors as prognosticators in cHL.

Sorafenib, a multikinase inhibitor, is effective in vitro against non-Hodgkin lymphoma and synergizes with the mTOR inhibitor rapamycin

Non-Hodgkin lymphoma (NHL) represents a heterogenous group of neoplasias originating from lymphoid cells. Increased angiogenesis and expression of Vascular Endothelial Growth Factor (VEGF) and its receptors (VEGFR) have been found to be associated with NHL disease progression. Increase in VEGF and other cytokines stimulate signaling cascades, including the Ras/Raf/Mek/Erk pathway, resulting in increased proliferation and decreased apoptosis. Here, we report the in vitro antilymphoma activity of sorafenib, an inhibitor of VEGFR and Raf kinase. Sorafenib induced potent cytotoxicity in NHL cell lines and patient samples. This induction of cytotoxicity was associated with a corresponding increase in apoptotic cell death. Mechanism of action of sorafenib was investigated in follicular (DoHH2) and Burkitt lymphoma (Raji) cell lines. pStat3, pAkt, Mcl1, and Xiap were downregulated in both cell lines, whereas pErk decreased in Raji but not in DoHH2 cells following sorafenib treatment. IL6 was unable to prevent sorafenib induced repression of pStat3, pAkt, Mcl1, and Bcl-Xl. Sorafenib in combination with an mTORC1 inhibitor rapamycin demonstrated synergy in inducing cytotoxicity in NHL cells. Sorafenib/rapamycin combination resulted in downregulation of pAkt, pmTOR, p-p70S6K, p4EBP1, pGSK3β, Mcl1, and Bcl-Xl. On the basis of our results, a clinical trial is underway using sorafenib with everolimus in NHL patients.

High serum angiogenin at diagnosis predicts for failure on long-term treatment response and for poor overall survival in non-Hodgkin lymphoma

BACKGROUND

Angiogenin is a potent inducer of angiogenesis. We prospectively evaluated the prognostic significance of serum angiogenin from 204 consecutive non-Hodgkin lymphoma (NHL) patients diagnosed and treated in a single institution.

METHODS

Serum angiogenin, VEGF, and bFGF concentrations at diagnosis were determined using a quantitative sandwich enzyme immunoassay technique. Kaplan-Meier survival curves were compared by the log-rank test. Multivariate survival analyses were performed using the parametric model of Weibull and the non-parametric proportional hazards model of Cox.

RESULTS

Patients with a high serum angiogenin at diagnosis (>median; 401 ng/ml) had significantly lower 5-year survival rate than those with a low (≤ median) angiogenin (42% versus 63%, respectively; P = 0.0073). Serum angiogenin provided additional information to the International Prognostic Index (IPI) identifying a subgroup (serum angiogenin >median and IPI>1) with very poor prognosis (5-year survival 19%, P < 0.0001). In receiver operating characteristic (ROC) analyses the accuracy of the IPI to correctly classify patients with favourable or poor survival was improved from fair to good by complementing the IPI with serum angiogenin concentration. With patients who initially achieved complete response (CR) after chemotherapy, a high angiogenin at diagnosis (>median; relative risk (RR) 2.38; P = 0.0077) and an advanced tumour stage (III-IV; RR 2.41; P = 0.0087) were the only independent predictors for patients with unfavourable outcome although first responding well to therapy.

CONCLUSIONS

We conclude that elevated serum angiogenin surfaced as an independent predictor for failure in long-term treatment response and for poor overall survival in a series of 204 NHL patients, and might thus also complement the IPI in identifying the patients with particularly aggressive and/or treatment resistant disease.

Clinical significance of serum vascular endothelial growth factor, endostatin, and leptin levels in children with lymphoma

BACKGROUND

A number of clinical studies conducted in adults have demonstrated the prognostic significance of angiogenic factors in malignancies, however, only a limited number of studies have been conducted in children. The aim of this study was to determine serum vascular endothelial growth factor (VEGF), endostatin, and leptin levels in children with lymphoma and to investigate whether these factors provide prognostic information.

PROCEDURE

Serum samples from 36 children with lymphoma (non-Hodgkin lymphoma (NHL) N = 21, Hodgkin lymphoma (HL) N = 15) were collected at diagnosis and during remission. Serum samples were also collected from 18 healthy children as the control group. Serum VEGF and endostatin levels were quantified by using enzyme-linked immunosorbent assay (ELISA) and serum leptin by immunoradiometric assay.

RESULTS

The serum VEGF levels were found elevated in patients compared to controls (P = 0.033), while endostatin and leptin levels were lower in patients than in controls (endostatin, 43.9 ± 5.8 ng/ml vs. 123.6 ± 13.5 ng/ml, P < 0.001; leptin, 5 ± 1.5 ng/ml vs. 6.7 ± 1.2 ng/ml, P = 0.013). VEGF levels declined (pre, 151.6 ± 55.9 pg/ml vs. post, 16.2 ± 7.9 pg/ml, P = 0.041), while endostatin and leptin levels increased in patients who achieved remission (33 of 36 patients) when compared to pre-treatment levels (endostatin pre, 43.1 ± 5.9 ng/ml vs. post, 65.9 ± 6.8 ng/ml, P = 0.047; leptin, pre, 5.3 ± 1.6 ng/ml vs. post, 9.8 ± 2.7 ng/ml, P = 0.012). Serum VEGF, endostatin, and leptin levels were not predictive of survival.

CONCLUSION

Serial measurement of serum VEGF, endostatin, and leptin levels could potentially be used to predict response to treatment or progressive disease in children with lymphoma.

Phase II trials of single-agent anti-VEGF therapy for patients with chronic lymphocytic leukemia

Between 2005 and 2008, we conducted separate phase II clinical testing of three distinct anti-VEGF therapies for patients with relapsed/refractory CLL. Collectively, 46 patients were accrued to trials of single-agent anti-VEGF antibody (bevacizumab, n = 13) or one of two receptor tyrosine kinase inhibitors (AZD2171, n = 15; sunitinib malate, n = 18). All patients have completed treatment. Patients received a median of two cycles of bevacizumab, AZD2171, or sunitinib malate. All three trials were closed early due to lack of efficacy. No complete or partial remissions were observed. Individually and collectively, these studies indicate that single-agent anti-VEGF therapy has minimal clinical activity for patients with relapsed/refractory CLL.

Assessment of bone marrow microvessel density in chronic lymphocytic leukemia

INTRODUCTION

Angiogenesis is a physiologic process of new blood vessels formation mediated by various cytokines called proangiogenic and antiangiogenic factors. Enhancement of angiogenesis in chronic lymphocytic leukemia (CLL) has been recognized more recently. Our study assesses CD34 and von Willebrand factor (vWf) expression and microvessel density (MVD) in the bone marrow of patients with CLL.

AIMS

(1) To assess bone marrow MVD in CLL using 2 different monoclonal antibodies, CD34 and vWf; and (2) To examine the possible association of marrow MVD and clinical course, pattern of marrow infiltration, Rai stage, CD38 positivity, and cytogenetic abnormalities detected by fluorescence in situ hybridization.

MATERIALS AND METHODS

Bone marrow specimens from 33 patients with CLL and 10 controls were studied. A single microvessel was defined as any vessel with a clear lumen. The screening of the slides was carried out by hotspot method. The slides were initially screened at low power to identify the areas with highest number of microvessel or vascularity hotspot. The count of microvessel in a sufficiently extended field (40x objective lens, 10x ocular lens) was then performed. The mean value of 10 most vascularized areas at 400x field was considered as MVD for a sample.

RESULTS

There was a significant difference between MVD counts according to the antibody used. MVD was higher using CD34 versus vWF (CD34: mean +/- SD, 35.91+/-15.7; 95% confidence interval of mean, 30.34-41.48 vessels/field versus vWF: 8.15+/-4.65; 95% confidence interval of mean, 4.11-12.44 vessels/field; P<0.0001]. Bone marrow MVD detected by CD34 was significantly higher in patients with CD38 expression more than 30% (P=0.006) and in patients with unfavorable cytogenetic abnormalities. However, no significant MVD differences were detected between CLL subgroups with regard to clinical course, pattern of marrow infiltration, and Rai stage. Bone marrow MVD in patients with CLL was significantly higher than that in controls (P<0.0001).

CONCLUSIONS

MVD assessment using anti-CD34 resulted in higher MVD counts than when using anti-vWF antibody. However, no MVD differences were detected between CLL subgroups subdivided according to the above-mentioned prognostic factors except CD38 expression and genetic abnormalities.

Vascular endothelial growth factor-related pathways in hemato-lymphoid malignancies

Angiogenesis is essential for malignant tumor growth. This has been documented for solid tumors, and there is an emerging evidence suggesting that tumor progression of hematolymphoid malignancies also depends on the induction of new blood vessel formation. The most important proangiogenic agent is vascular endothelial growth factor (VEGF), activating VEGF receptors 1 and 2. The available data on angiogenesis in hemato-lymphoid malignancies, such as acute leukemias, myelodysplastic syndromes, myeloproliferative neoplasms, multiple myeloma, and lymphomas, point towards the significance of autocrine and paracrine VEGF-mediated effects for proliferation and survival of leukemia/lymphoma cells in addition to tumor vascularization. Antiangiogenic strategies have become an important therapeutic modality for solid tumors. Several antiangiogenic agents targeting VEGF-related pathways are also being utilized in clinical trials for the treatment of hemato-lymphoid malignancies, and in some instances these pathways have emerged as promising therapeutic targets. This review summarizes recent advances in the basic understanding of the role of angiogenesis in hemato-lymphoid malignancies and the translation of such basic findings into clinical studies.

Vascular endothelial growth factor concentrations from platelets correlate with tumor angiogenesis and grading in a spontaneous canine non-Hodgkin lymphoma model

Published data strongly suggest that tumor progression and malignancy are associated with increased angiogenesis. However, no data have been published concerning the relationship between microvascular density (MVD), tumor cytosol, and blood vascular endothelial growth factor (VEGF) concentrations in canine non-Hodgkin lymphoma (C-NHL), a neoplasm that shares biological and clinical characteristics with human NHL. We have evaluated MVD and tumor cytosol, serum (S), platelet-poor plasma (P-PP), plasma-activated platelet rich (P-APR) VEGF concentration in a series of 63 B-cells C-NHL by means of immunohistochemistry and enzyme-linked immuno-sorbent assay (ELISA) detection of VEGF. We found that MVD, VEGF from cytosol, and VEGF from P-APR are significantly correlated (p ranging from 0.001 to 0.003) and that these parameters paralleled with the malignancy degree of NHL. Accordingly, spontaneous C-NHL seems to be an interesting model to study the role of angiogenesis as interspecies pathway of tumor malignancy and we suggest that VEGF from P-APR might be a novel useful circulating bio-marker of tumor angiogenesis.

Increased angiogenic sprouting in poor prognosis FL is associated with elevated numbers of CD163+ macrophages within the immediate sprouting microenvironment

Follicular lymphoma has considerable clinical heterogeneity, and there is a need for easily quantifiable prognostic biomarkers. Microvessel density has been shown to be a useful prognostic factor based on numerical assessment of vessel numbers within histologic sections in some studies, but assessment of tumor neovascularization through angiogenic sprouting may be more relevant. We therefore examined the smallest vessels, single-staining structures measuring less than 30 microm(2) in area, seen within histologic sections, and confirmed that they were neovascular angiogenic sprouts using extended focal imaging. Tissue microarrays composing diagnostic biopsies from patients at the extremes of survival of follicular lymphoma were analyzed with respect to numbers of these sprouts. This analysis revealed higher angiogenic activity in the poor prognostic group and demonstrated an association between increased sprouting and elevated numbers of infiltrating CD163(+) macrophages within the immediate microenvironment surrounding the neovascular sprout.

The role of macrophages in the development and progression of AIDS-related non-Hodgkin lymphoma

Despite HAART, patients infected with HIV develop NHL at a significantly higher level than the noninfected population. The primary difference between lymphoma in non-HIV-infected individuals and those with ARL is that ARL is consistently high-grade and metastatic. The emergence of ARL is associated with the presence of macrophage viral reservoirs, similar to what has been observed for HAD. HIV-infected macrophages, as seen by histology and HIV p24 staining, are present in approximately half of ARLs. Macrophage reservoirs recruit additional immune cells, including monocytes/macrophages, through the release of chemoattractants. Additionally, TAM are known to promote tumor progression for most cancer types, including lymphomas. This review will highlight and discuss the role of macrophage viral reservoirs in the development and progression of ARLs and hopefully, shed light on this new and interesting field.

Biological prognostic markers in chronic lymphocytic leukemia

Chronic lymphocytic leukemia (CLL) is the most frequent leukemic disease of adults in the Western world. It is remarkable by an extraordinary heterogeneity of clinical course with overall survival ranging from several months to more than 15 years. Classical staging sytems by Rai and Binet, while readily available and useful for initial assessment of prognosis, are not able to determine individual patient's ongoing clinical course of CLL at the time of diagnosis, especially in early stages. Therefore, newer biological prognostic parameters are currently being clinically evaluated. Mutational status of variable region of immunoglobulin heavy chain genes (IgVH), cytogenetic aberrations, and both intracellular ZAP-70 and surface CD38 expression are recognized as parameters with established prognostic value. Molecules regulating the process of angiogenesis are also considered as promising markers. The purpose of this review is to summarize in detail the specific role of these prognostic factors in chronic lymphocytic leukemia.

The prognostic significance of VEGF-C and VEGF-A in non-Hodgkin lymphomas

Angiogenesis and lymphangiogensis are important in the proliferation and survival of the malignant hemeopoietic neoplasms. The aim of this study is to determine the prognostic role of angiogenesis and lymphangiogenesis in the development of lymphoma. For this aim, VEGF-A and VEGF-C were explored by immunohistochemistry in 177 cases. VEGF-C and VEGF-A were found to be positive in 34 and 61% of the samples. There was a good correlation between VEGF-C and VEGF-A expression (p = 0.0001). The clinical prognostic indicators were not significantly different between VEGF-C (+) and (-) and/or VEGF-A (+) and (-) cases. Overall survival (OS) rate was shorter in cases with VEGF-A (+) and VEGF-C (+) cases than with negative cases (p = 0.03 and p = 0.0005, respectively). The OS was significantly shorter in aggressive lymphomas expressing VEGF-A and VEGF-C but not in indolent lymphomas. The results of Cox regression analyses showed that VEGF-A and VEGF-C expressions are independent prognostic parameters (OR: 2.6, 95% CI: 1.3-5.0 for both (+) cases). In conclusion, VEGF-C and VEGF-A were positive in 34 and 61%, respectively, of the cases with NHL. The significant correlation between VEGF-C and VEGF-A suggests that lymphangiogenesis is important in the pathogenesis of lymphomas as shown in angiogenesis. The significantly shorter survival rates of VEGF-C and/or VEGF-A expressions indicate that angiogenesis and lymphangiogenesis are important in clinical outcome. Autocrine VEGF-A and VEGF-C crosstalks in lymphoma cells are important in lymphoma biology and inhibition of these signals with anti-angiogenic/anti-lymphangiogenic drugs and combination with chemo-immunotherapy regimens will be more useful in these cases.

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.

Angiogenesis and antiangiogenic therapy in non-Hodgkin's lymphoma

Angiogenesis, the growth of new blood vessels, requires dynamic expansion, assembly and stabilization of vascular endothelial cells in response to proangiogenic stimuli. Antiangiogenic strategies have become an important therapeutic modality for solid tumors. While many aspects of postnatal pathological angiogenesis have been extensively studied in the context of nonhematopoietic neoplasms, the precise role of these processes in lymphoma pathogenesis is under active investigation. Lymphoma growth and progression is potentiated by at least two distinct angiogenic mechanisms: autocrine stimulation of tumor cells via expression of vascular endothelial growth factor (VEGF) and VEGF receptors by lymphoma cells, as well as paracrine influences of proangiogenic tumor microenvironment on both local neovascular transformation and recruitment of circulating bone marrow-derived progenitors. Lymphoma-associated infiltrating host cells including hematopoietic monocytes, T cells and mesenchymal pericytes have increasingly been associated with the pathogenesis and prognosis of lymphoma, in part providing perivascular guidance and support to neoangiogenesis. Collectively, these distinct angiogenic mechanisms appear to be important therapeutic targets in selected non-Hodgkin's lymphoma (NHL) subtypes. Understanding these pathways has led to the introduction of antiangiogenic treatment strategies into the clinic where they are currently under assessment in several ongoing studies of NHL patients.

Complete eradication of human B-cell lymphoma xenografts using rituximab in combination with the immunocytokine L19-IL2

The antibody-mediated delivery of therapeutic agents to sites of angiogenesis is an attractive strategy for anticancer therapy, but is largely unexplored in hematologic malignancies. In the present study, we show that the extra domain B (EDB) of fibronectin, a marker of angiogenesis, is expressed in B-cell non-Hodgkin lymphoma (NHL) and that the human monoclonal anti-EDB antibody L19 can selectively localize to the lymphoma-associated subendothelial extracellular matrix. In vivo, the preferential accumulation of the antibody at the tumor site was confirmed by quantitative biodistribution analyses with radioiodinated antibody preparations. The fusion protein L19-IL2, which mediates the delivery of interleukin-2 (IL-2) to the neovasculature, displayed a superior antilymphoma activity compared with unconjugated IL-2 in localized and systemic xenograft models of NHL. When coadministered with rituximab, L19-IL2 induced complete remissions of established localized lymphomas and provided long-lasting protection from disseminated lymphoma. The combined use of rituximab and L19-IL2, which dramatically increases the infiltration of immune effector cells in lymphomas, may deserve clinical investigations, facilitated by the fact that L19-IL2 is currently being studied in phase II clinical trials in patients with solid tumors.

Tumor versus tumor-associated macrophages: how hot is the link?

One of the functions of macrophages is to provide a defense mechanism against tumor cells. In contrast, tumor-associated macrophages (TAMs), which represent the major inflammatory component of the stroma of many tumors, are associated with tumor progression and metastasis. TAMs, in contrast with normal macrophages, exhibit the M2 phenotype, and thereby exhibit pro-tumoral functions, including angiogenesis and matrix remodeling. This review will discuss the role of TAMs in tumor progression and provide an overview of their significant part in tumor metastasis and angiogenesis.

A high-affinity human monoclonal antibody specific to the alternatively spliced EDA domain of fibronectin efficiently targets tumor neo-vasculature in vivo

The alternatively spliced extra-domain B of fibronectin is one of the best characterized markers of tumor angiogenesis. Similarly, the extra-domain A (EDA), which can also be inserted in the fibronectin transcript by a mechanism of alternative splicing, has been shown to preferentially accumulate around new blood vessels in certain tumors, but this antigen has not been investigated so far as a target for antibody-based biomolecular intervention. We here describe the generation of 3 human monoclonal antibodies (named F8, B7 and D5), which recognize the same epitope of EDA, but which differ in terms of their dissociation constant to the human antigen (K(D) = 3.1, 16 and 17 nM, measured for monomeric preparations of the F8, B7 and D5 antibodies, respectively, in recombinant scFv format). When the 3 antibody fragments were cloned and expressed with a 5 amino acid linker, the 3 resulting homodimeric antibody preparations displayed comparable tumor: organ ratios in quantitative biodistribution studies, performed in immunocompetent 129SvEv mice, bearing subcutaneous syngeneic F9 murine tumors. The percent injected dose per gram (%ID/g) values in tumors 24 hr after intravenous injection were 9.3, 10.2 and 13 for F8, B7 and D5, respectively. The F8 antibody may serve as useful building block for the development of antibody-based targeted anti-cancer therapeutics. Preclinical and clinical investigations are facilitated by the fact that F8 recognizes the human and mouse antigen with comparable affinity, and by the observation that EDA over-expression is detectable not only in solid tumors, but also in hematological malignancies.

Clinical correlations and prognostic relevance of HGF, VEGF AND FGF expression in Brazilian patients with non-Hodgkin lymphoma

The aims of this study were to correlate HGF, VEGF and FGF serum levels and microvessel density (MVD) with cell origin, biological behavior, tumor load and prognosis in NHL. Eighty-seven consecutive previously untreated NHL patients had serum samples collected; 37 (42%) of them also had serum follow-up samples; the control group was composed of 10 healthy blood donors. Cytokine serum levels were determined by ELISA, and MVD was measured by CD34 staining in paraffin blocks. HGF mean serum level was significantly higher in both early and advanced NHL stages when compared with the control group. HGF was also significantly higher in aggressive and indolent NHL when compared with the control group. Also, mean serum level of HGF in aggressive NHL was significantly higher than in indolent NHL. Regarding International Prognostic Index (IPI), HGF mean serum level at diagnosis was significantly higher for patients with IPI >2 when compared to IPI <or=2. Sequential analyses of HGF, VEGF and FGF serum levels in NHL showed that serum HGF and VEGF levels decreased significantly after 6 months of treatment completion. Our findings suggest that HGF serum level is associated with tumor load and aggressiveness, and response to treatment results in a decrease in HGF serum levels in NHL patients.

Angiogenesis-related growth factors and cytokines in the serum of patients with B non-Hodgkin lymphoma; relation to clinical features and response to treatment

Increased angiogenesis has been shown to be a feature of non-Hodgkin lymphomas (NHL). In the current study, the pretreatment levels of circulating molecules related to angiogenesis were determined in 49 B-cell NHL patients and correlated with histological grade, disease stage and prognostic score. In 25 patients, the same molecules were defined after standard treatment. Vascular endothelial growth factor (VEGF), angiogenin, interleukin-2 (IL-2), IL-6, IL-8 and IL-16 were measured. Increased levels of VEGF, IL-6 and IL-8 were found in the whole group of untreated patients in comparison with normal controls (P < 0.05), whereas, IL-2 was higher in the subgroup of indolent NHL. Overall, there was no significant decrease in the levels of these molecules after treatment. However, by stratification into group of responders vs. non-responders pretreatment IL-8 was significantly increased whereas IL-16 was decreased in the subgroup of complete responders. According to the REAL classification IL-2 was higher in the low risk compared with intermediate plus high-risk group. There was no association with disease stage or the International Prognostic Score. Both indolent and aggressive B cell lymphomas have increased production of angiogenic mediators and cytokines with IL-8 and IL-16 potentially reflecting the response to treatment.

Microvascular density and endothelial area correlate with Ki-67 proliferative rate in the canine non-Hodgkin's lymphoma spontaneous model

Experimental and clinical data indicate that tumor progression and malignancy are associated with increased angiogenesis and higher Ki-67 proliferation rate. Furthermore, increased angiogenesis and higher Ki-67 proliferation rate are associated with a poor prognosis, in both solid and hematological malignancies. However, no data have been published concerning the relationship between angiogenesis and Ki-67 proliferation rate in canine non-Hodgkin's lymphoma (NHL), a neoplasm that shares several biological and clinical characteristics with human NHL. This study has evaluated the relationship between angiogenesis and Ki-67 proliferation rate in a series of 58 canine NHL. Results showed that microvascular density (MVD), endothelial area (EA) and Ki-67 (MIB-1) are significantly correlated and that all the above indexes paralleled with the malignancy degree of NHL. These data suggest a biological link between angiogenesis and Ki-67 proliferation rate in canine NHL, which represents an interesting model to study the role of angiogenesis and proliferative activity as inter-species pathways of tumoral malignancy and biological aggressiveness.

Angiogenesis in primary central nervous system lymphoma (PCNSL)

Angiogenesis and angiogenic growth factors have a major role in the pathogenesis of malignancies. However, very little is known about the clinical and histopathological relevance of angiogenesis in primary central nervous system lymphoma (PCNSL). We investigated that expression of vascular endothelial growth factor (VEGF) of the lymphoma cells and microvessel density (MVD) were examined in 19 patients with PCNSL. Additionally, the presence of the blood-brain barrier (BBB) was examined using immunohistochemistry and the electron microscopy. MVD was significantly higher in nine cases with VEGF immunoreactivity (VEGF+) than in ten cases with negative immunoreactivity for VEGF (VEGF-) (P < 0.001). VEGF expression was significantly associated with a longer survival (P < 0.005). BBB markers were negative in angiogenic vessels of VEGF+. BBB markers were identified in vessels surrounding tumor cells and tight junctions were also preserved in the capillary endothelium surrounding tumor cells in VEGF-. Angiogenesis is associated with VEGF expression and an absent BBB in the vessels of PCNSL. The BBB may be preserved in lesions with lymphoma cell infiltration, especially in VEGF- PCNSL. VEGF may have a prognostic effect in PCNSL.

High-Dose Celecoxib and Metronomic “Low-dose” Cyclophosphamide Is an Effective and Safe Therapy in Patients with Relapsed and Refractory Aggressive Histology Non–Hodgkin's Lymphoma

PURPOSE

Angiogenesis is increased in aggressive histology non-Hodgkin's lymphoma and may be a target with selective cyclooxygenase-2 inhibition and metronomic chemotherapy.

EXPERIMENTAL DESIGN

We assessed response, toxicity, and biomarkers of angiogenesis to low-dose cyclophosphamide (50 mg p.o. o.d.) and high-dose celecoxib (400 mg p.o. b.i.d.) in adult patients with relapsed or refractory aggressive non-Hodgkin's lymphoma in a multicenter phase II prospective study.

RESULTS

Thirty-two of 35 patients (median age, 62 years) are evaluable for response. Patients had primarily relapsed diffuse large B-cell lymphoma (63%) were heavily pretreated (median of three regimens) and high risk (79% international prognostic index, >or=2) and 34% were relapsed after autologous stem cell transplant. With a median follow-up of 8.4 months, the overall best response rate is 37% (2 complete clinical response/complete clinical response unconfirmed and 9 partial response), with 22% achieving stable disease. Median overall and progression-free survivals are 14.4 and 4.7 months, respectively. The median response duration was 8.2 months. The most common toxicity was skin rash (40%); myelosuppression and gastrointestinal side effects were uncommon. Three patients developed deep vein thromboses and two heavily pretreated patients developed treatment-related acute myelogenous leukemia or myelodysplasia after 3.7 and 12 months of therapy. Circulating endothelial cells and their precursors declined and remained low in responders, whereas plasma vascular endothelial growth factor trended to decline in responding patients but increase in nonresponders. Trough celecoxib levels achieved targeted "antiangiogenic" levels.

CONCLUSIONS

Low-dose cyclophosphamide and high-dose celecoxib is well tolerated and active in pretreated aggressive non-Hodgkin's lymphoma. Close surveillance for arterial and venous thrombotic events is recommended. The decline in circulating endothelial cells and their precursors suggests that this combination may be working by inhibiting angiogenesis but should be validated in a larger patient sample.

Angiogenesis in nodal B cell lymphomas: a high throughput study

AIM

To assess the biological significance of vascular endothelial growth factor (VEGF) A, VEGF receptor (Flk-1) and cyclooxygenase 2 (COX2) expression with respect to microvessel density (MVD), proliferative activity (Ki-67), expression of p53 and clinical presentation in a large cohort of nodal B cell lymphomas.

METHODS

An immunohistochemical and morphometric study was performed on a validated tissue microarray containing 271 B cell lymphoma specimens, 197 of which included follow-up data. Statistical assessment was done by Pearson's chi(2) test, Spearman's rank correlation coefficient, analysis of variance and survival analysis.

RESULTS

266 (98%) cases were evaluable. Strong VEGF expression was observed in only 20 diffuse large B cell lymphomas (DLBCLs). Flk-1 and COX2 were expressed in 53 and 21 cases, respectively, mainly in DLBCLs, follicular lymphoma (FL) grade 3 and mantle cell lymphomas (MCLs), in a low proportion of cells. MVD decreased in the following order: DLBCLs, FLs, MCLs and small lymphocytic lymphomas/chronic lymphocytic leukaemia (SLL/CLLs). VEGF expression correlated with Ki-67, p53 and COX2 expression in the whole cohort and in DLBCLs. Flk-1 expression correlated with Ki-67 in the cohort and in SLL/CLL and FL grade 1 and 2. COX2 expression correlated with Ki-67 and p53. The analysed angiogenesis parameters did not correlate with clinical parameters or survival.

CONCLUSIONS

Angiogenesis plays a differential role in various B cell lymphomas. Aggressive lymphomas express the potential molecular therapeutic targets VEGF and COX2, and have higher MVD. In a few low proliferation-fraction lymphomas, Flk-1 might have a role in proliferative advantage. Therapeutic strategies aimed at angiogenesis should take into account lymphoma heterogeneity.

Macrophages promote angiogenesis in human breast tumour spheroids in vivo

An in vivo model has been established to study the role of macrophages in the initiation of angiogenesis by human breast tumour spheroids in vivo. The extent of the angiogenic response induced by T47D spheroids implanted into the dorsal skinfold chamber in nude mice was measured in vivo and compared to that induced by spheroids infiltrated with human macrophages prior to implantation. Our results indicate that the presence of macrophages in spheroids resulted in at least a three-fold upregulation in the release of vascular endothelial growth factor (VEGF) in vitro when compared with spheroids composed only of tumour cells. The angiogenic response measured around the spheroids, 3 days after in vivo implantation, was significantly greater in the spheroids infiltrated with macrophages. The number of vessels increased (macrophages vs no macrophages 34±1.9 vs 26±2.5, P<0.01), were shorter in length (macrophages vs no macrophages 116±4.92 vs 136±6.52, P<0.008) with an increased number of junctions (macrophages vs no macrophages 14±0.93 vs 11±1.25, P<0.025) all parameters indicative of new vessel formation. This is the first study to demonstrate a role for macrophages in the initiation of tumour angiogenesis in vivo.