Co-expression of Thymidine Phosphorylase and Heme Oxygenase-1 in Macrophages in Human Malignant Vertical Growth Melanomas

Expression of thymidine phosphorylase (TP) is often associated with tumor angiogenesis and/or prognosis in patients. Further, infiltration of macrophages is closely correlated with the depth of tumor and angiogenesis in melanomas. In this study, we examined the expression of TP and an activated macrophage-specific enzyme, heme oxygenase-1 (HO-1), involved in malignancy in 22 cases with melanomas. TP was strongly expressed not only in CD68-positive macrophages in and around tumors, but also in S100 protein-positive melanoma cells, fibroblasts and keratinocytes. By contrast, HO-1 was specifically expressed in macrophages, but only slightly in melanoma cells and other cell types in the stroma of melanomas. We thus observed apparent co-expression of TP and HO-1 in macrophages infiltrating in the late stage of malignant melanomas. There appeared increasing numbers of TP-positive cells in Clark level IV and V melanoma compared with Clark level I ( in situ ) melanoma, and there was also a close correlation between numbers of TP-positive cells and HO-1-positive cells. Both TP- and HO-1-positive macrophages could be observed in the stroma in and around tumors in vertical growth melanomas.     

MACG1, a mouse monoclonal antibody detecting a monosialoganglioside expressed in tumor-infiltrating macrophages

MacG1 is a mouse monoclonal antibody (mAb) directed against a ganglioside, which is differentially expressed by macrophages infiltrating malignant melanomas and benign melanocytic lesions. mAb MacG1 was obtained by immunization with liposomes containing a mixture of gangliosides extracted from malignant melanoma. The antibody was selected for binding to melanoma gangliosides and for reactivity with frozen tissue sections of malignant melanoma. mAb MacG1 showed reactivity in 25 of 46 melanomas examined but in only 1 of 51 nevi tested. The mAb did not react with melanoma cells but did with cytoplasmic granules and deposits associated with large dispersed cells, which were also found in some nonmelanomatous tumors and in some lymphoid tissues. Using mAbs directed against differentiation antigens these cells were identified as macrophages. In nearly all reactive tissues MacG1-positive macrophages accounted for a minority of the total macrophages. The difference in reactivity between malignant melanomas and nevi could not be explained by the variable numbers of total macrophages in these lesions. It is suggested that mAb MacG1 may define a functionally distinct subpopulation of tumor-infiltrating macrophages. Staining of cells other than macrophages was observed in some normal and malignant neural tissues. MacG1 bound to a monosialoganglioside extracted from melanoma and reacted only with NeuAc alpha 2-3Gal beta 1-4Glc-Cer when tested with a panel of ganglioside standards.     

The effect of a thymidine phosphorylase inhibitor on angiogenesis and apoptosis in tumors

Thymidine phosphorylase (TP) is an enzyme involved in the reversible conversion of thymidine to thymine and is identical to an angiogenic factor, platelet-derived endothelial cell growth factor. TP is expressed at higher levels in a wide variety of solid tumors than in the adjacent nonneoplastic tissues. Patients with TP-positive colon and esophageal tumors have a poorer prognosis than those with TP-negative tumors. We have recently synthesized a new TP inhibitor (TPI), 5-chloro-6-[1-(2-iminopyrrolidinyl) methyl] uracil hydrochloride. We investigated the effect of TPI on angiogenesis in KB cells transfected with platelet-derived endothelial cell growth factor cDNA, KB/TP, and a mock transfectant, KB/CV, using the mouse dorsal air sac assay model. We found that KB/TP cells had a higher angiogenic ability than KB/CV cells and that TPI completely suppressed angiogenesis by KB/TP. Furthermore, at a dose of 50 mg/kg/day, TPI considerably decreased the growth rate of KB/TP cells xenografted into nude mice. Microvessel density in KB/TP tumors was higher than that in KB/CV tumors, and TPI did not significantly change the density in either of the tumors. The apoptotic index in KB/TP tumors was significantly lower than that in KB/CV tumors, and TPI significantly increased the apoptotic index in KB/TP tumors but not in KB/CV tumors. These findings, taken together with previous reports, suggest that the expression of TP plays an important role in tumor growth and that TPI suppresses tumor growth by increasing the proportion of apoptotic cells and probably inhibiting angiogenesis.     

Macrophage infiltration-associated thymidine phosphorylase expression correlates with increased microvessel density and poor prognosis in astrocytic tumors.

PURPOSE AND EXPERIMENTAL DESIGN: To clarify the significance of thymidine phosphorylase (TP)/platelet-derived endothelial cell growth factor/gliostatin in human glioma, we examined TP expression immunohistochemically in a series of 50 astrocytic tumors and correlated its expression with tumor angiogenesis and apoptosis, as well as prognosis. RESULTS: The majority of TP-positive cells were of macrophage origin, which was confirmed by immunostaining TP and CD68 on mirror sections. TP expression was significantly associated with glioma malignancy grading, intratumoral microvessel density, and VEGF expression but showed no relationship with apoptotic index or P53 expression. Regardless of glioma grading, patients with TP-positive tumors had a significantly shorter mean survival time than those with TP-negative tumors. CONCLUSIONS: These findings suggest that TP might play a crucial role in angiogenesis during glioma development, and immunodetection of TP is useful for clinical prediction. Further studies are necessary to better elucidate the role of TP in glioma, which may provide insights into adequate TP-targeted therapy.     

Identification of a novel gelsolin truncate in the vertical and metastatic phase malignant melanomas

Examination of 38 human melanoma samples by Western blotting analysis with anti-gelsolin antibodies showed that a new 85 kDa truncated gelsolin (GSNp85), co-expressed with wild-type gelsolin, was frequently expressed in vertical growth phase melanomas (Clark level II-IV) and metastatic growth phase melanomas. The GSNp85 truncate was not expressed in radial growth phase melanomas (Clark level I), acquired naevi, other skin cancers or normal skin tissues. Peptide-sequencing analysis revealed that GSNp85 lacks the C-terminal domain of wild-type gelsolin at the region containing the caspase-8 recognition site IETD. Caspase-8 processing was detected in GSNp85-positive but not GSNp85-negative melanomas. These data suggest that GSNp85 is a cleavage product of caspase-8 and may be useful as a new marker for the vertical or metastatic growth phase of malignant melanoma.     

Loss of expression of the p16INK4/CDKN2 gene in cutaneous malignant melanoma correlates with tumor cell proliferation and invasive stage

The G₁/S checkpoint of the cell cycle is regulated by p16, p53 and RB tumor suppressor genes. Loss of expression of the p16^INK4 tumor suppressor protein, the product of the CDKN2 gene, has been associated with a wide variety of human malignancies. Mutations, loss of heterozygosity and deletions of the CDKN2 locus have been reported in sporadic and familial cutaneous malignant melanomas (CMM). To investigate the role of the alterations of p16 expression in melanoma, we evaluated by immunohistochemistry the p16 expression and cell proliferation in 79 primary CMM and 10 benign melanocytic nevi (BMN). Forty-six melanomas (58%) and all BMN were found to be p16 positive; 33 melanomas (42%) were considered p16 negative. The extent of invasion according to Clark was significantly higher in p16-negative tumors than in p16-positive tumors. Cell proliferation as expressed by the proportion of positive cells in Ki-67 immunostaining was found to be significantly higher in p16-negative tumors than in p16-positive tumors, although there was no significant difference in the mitotic index between p16-positive and p16-negative tumors. In p16-positive tumors, the number of Ki-67-positive cells correlated with the mitotic index; in p16-negative tumors, there was no correlation between these parameters. Our data suggest that loss of p16 expression is more common in advanced melanomas, and that G₁/S checkpoint regulation is disrupted in p16-negative melanomas. Our results show that loss of p16 expression is a common event in primary melanomas, which further substantiates the role of p16 as a major tumor suppressor. Int. J. Cancer 74:255-259, 1997. © 1997 Wiley-Liss, Inc.     

Expression of CD44s and CD44 splice variants in human melanoma.

The ability of tumor cells to adhere and detach from extracellular matrix and endothelial cells, is a crucial step in the metastatic process and may alter the clinical prognosis of some human tumors such as melanomas. CD44, the major cell surface receptor for hyaluronate, has been implicated in cell adhesion and in tumor progression. We studied the expression of standard CD44 molecule (CD44s) and its variants v3 and v6 in 57 human primary melanoma biopsies, without previous treatment. We analyzed the association between CD44 expression and the principal clinicopathological features, including survival. Fifty-six of 57 tumors expressed CD44s, associated to the cytoplasmic membrane. No expression of CD44v3 or CD44v6 was detected. No association between CD44s expression and prognostic factors such as tumor thickness, growth type, stage or anatomic site of the lesion was found. However, a positive correlation between CD44s expression and Clark level (Spearman, p<0.001) was found. While only 33.3% of melanomas Clark I + II showed high expression of CD44s (more than 50% of positive cells), 82.6% of melanomas Clark IV + V did so. Kaplan-Meier analysis revelead that patients whose melanomas had high expression of CD44s showed a reduced relapse free survival (RFS) rate, though without statistical significance. No difference between the level of CD44 expression and overall survival (OS) was found. We conclude that melanomas only expressed CD44s, and that its level was associated with Clark's stage. CD44s seems not to be useful as a tumor marker, because it does not predict either RFS or OS.     

Immunohistochemical expression of VEGF, HIF1-a, and PlGF in malignant melanomas and dysplastic nevi

We evaluated the role of vascular endothelial growth factor (VEGF), placental growth factor (PlGF), and hypoxia-inducible factor 1-a (HIF1-a) in melanoma angiogenesis and investigated their expression in dysplastic nevi, as potential melanoma precursors. In addition, we examined a possible correlation of VEGF expression with PlGF and HIF1-a. These factors were detected immunohistochemically in 95 melanomas of all types and stages and in 28 dysplastic nevi. We used 10 intradermal melanocytic nevi as controls. HIF1-a was expressed in 93 out of 95 (97.89%) melanomas and in none of the dysplastic or control nevi. HIF1-a expression was more intense in melanocytes around necrotic areas but did not correlate with melanoma type, the Clark staging or the Breslow thickness. A strong positive association was detected between HIF1-a and VEGF expression in all cases. VEGF was detected in 82 out of 95 (86.31%) melanomas and in 21 out of 28 (75%) dysplastic nevi, whereas it was expressed weakly in neoplastic cells of the controls. Its expression was more intense in melanomas, especially in nodular melanomas of elevated stage and thickness. PIGF was detected in 46 out of 95 (48.42%) melanomas and in none of the nevi. Expression did not correlate with melanoma staging nor thickness; however, it was more intense in superficial spreading melanomas, where a weak positive association between VEGF and PlGF was also detected. There was no association between HIF1-a and PlGF in any melanoma type. Hypoxia, through the expression of HIF1-a, plays a key role in melanoma progression; it activates VEGF secretion, which induces angiogenesis and metastasis. The role of PlGF seems to be limited.     

Significance of thymidine phosphorylase/platelet-derived endothelial cell growth factor in carcinoma of the papilla of Vater.

The expression of thymidine phosphorylase (TP) in carcinoma of the papilla of Vater was studied to clarify its significance in tumor progression and in determining prognosis. Fifty-nine cases of surgically resected carcinoma of the papilla of Vater were studied. Immunohistochemical staining was performed to evaluate the expression of TP, microvessel count and p53 overexpression. TP expression was demonstrated in tumor cells in 62.7% (37/59) of the cases. A higher frequency of regional lymph node metastasis was found in TP-positive tumors than in TP-negative tumors (P = 0.006). TP-positive tumors were more advanced than TP-negative tumors with regard to clinical stage (P = 0.035). TP-positive tumors had significantly higher microvessel density (27.6 +/- 10.1) than TP-negative tumors (20.4 +/- 10.0, P = 0.01). Moreover, TP expression was significantly correlated with a poor prognosis (P = 0. 02). These suggest that in carcinoma of the papilla of Vater, TP production by tumor cells is correlated with tumor progression through its regulatory effect on neovascularization.     

L1 adhesion molecule (CD 171) in development and progression of human malignant melanoma

The L1 adhesion molecule (CD171) plays an important role in axon guidance and cell migration in the nervous system. In the human, L1 is expressed on tumors derived from neurocrest and on certain carcinomas. We have analyzed immunohistochemically L1 expression on paraffin embedded specimens of acquired melanocytic nevi, primary cutaneous melanomas, and cutaneous and lymph node metastases of malignant melanomas. We found an increase in L1 immunoreactivity in malignant melanomas and metastases of malignant melanomas as compared to acquired melanocytic nevi that was statistically significant (P<0.05). Additionally, a correlation of L1 immunoreactivity with histological data of prognostic value such as Clark level and the expression of alphav-integrins was found. We detected soluble L1 in the conditioned medium of cultivated melanoma cells but only in 1/40 serum samples from a panel of melanoma patients representing various stages of disease. Our findings suggest that the presence of L1 might contribute to tumor progression by promoting cell adhesion and migration.     

Significance of Thymidine Phosphorylase/Platelet-derived Endothelial Cell Growth Factor in Carcinoma of the Papilla of Vater

The expression of thymidine phosphorylase (TP) in carcinoma of the papilla of Vater was studied to clarify its significance in tumor progression and in determining prognosis. Fifty-nine cases of surgically resected carcinoma of the papilla of Vater were studied. Immunohistochemical staining was performed to evaluate the expression of TP, microvessel count and p53 overexpression. TP expression was demonstrated in tumor cells in 62.7% (37/59) of the cases. A higher frequency of regional lymph node metastasis was found in TP-positive tumors than in TP-negative tumors ( P =0.006). TP-positive tumors were more advanced than TP-negative tumors with regard to clinical stage ( P =0.035). TP-positive tumors had significantly higher microvessel density (27.6±10.1) than TP-negative tumors (20.4±10.0, P =0.01). Moreover, TP expression was significantly correlated with a poor prognosis ( P =0.02). These suggest that in carcinoma of the papilla of Vater, TP production by tumor cells is correlated with tumor progression through its regulatory effect on neovascularization.     

Expression of cyclooxygenase-2 and inducible nitric oxide synthase in human ovarian tumors and tumor-associated macrophages

This study investigates whether and to what extent cyclooxygenase type-2 (COX-2) and inducible nitric oxide-synthase (iNOS), both known to have an immunosuppressive effect, are expressed in human ovarian tumors. Because COX-2 and iNOS can be expressed by activated macrophages, the presence of tumor-associated macrophages and the expression of COX-2 and iNOS by these tumor-associated macrophages were determined. The results obtained may provide insight into the function of COX-2 and iNOS expression by tumors. The expression of COX-2 and iNOS in tumor cells and macrophages was assessed in 18 malignant, 15 borderline, and 14 benign human ovarian tumors by immunohistochemical staining of frozen tissue sections. The intra- and peritumoral macrophages were stained using an anti-CD68 monoclonal antibody. Most of the malignant tumors (15 of 18), 10 of 15 borderline, and 9 of 14 benign tumors showed COX-2 expression in the epithelial cells, a result which indicates that COX-2 expression is not exclusive to malignancy. In addition, COX-2 staining was more intense in the epithelial cells of benign and borderline tumors than in malignant tumors. Weak iNOS staining was observed in 5 of 18 malignant, 4 of 15 borderline, and 5 of 14 benign tumors. The number of tumor-associated macrophages varied widely between the different tumors. The highest number of tumor-associated macrophages (> or =20/0.125 mm(2)) was observed in malignant tumors, whereas low to moderate intra- and peritumoral macrophage infiltration (5-20/0.125 mm(2)) was observed in the borderline and benign tumors. COX-2-positive tumor-associated macrophages were found in 3 of 18 malignant tumors, 7 of 15 borderline tumors, and 1 of 14 benign tumors. The number of COX-2-positive tumor-associated macrophages ranged from 3 to 30% of the total macrophage population. Some malignant (4 of 18), borderline (5 of 15), and benign (2 of 14) tumors contained iNOS-positive macrophages. Notable was that COX-2- and iNOS-positive macrophages were predominantly located in the tumor stroma, the regions between tumor and stroma, and in the lumina of the tumor when located in the tumor tissue. These data indicate that not only malignant but also borderline and benign ovarian tumors can exhibit increased levels of COX-2 and iNOS expression. In addition, a small proportion of the tumor-associated macrophages found in malignant, borderline, and benign tumors seems to be in an activated state, judged by their iNOS and COX-2 expression. This subpopulation of tumor-associated macrophages was invariably located in the tumor stroma or in the lumina of the tumor, specifically suggesting that macrophages outside the tumor can be tumor cytotoxic.     

Structure, expression and chromosome mapping of MLZE, a novel gene which is preferentially expressed in metastatic melanoma cells.

We isolated a novel gene, termed MLZE, from a B16-BL6 cDNA library after subtraction of B16-F10 mRNA. Expression levels of mouse MLZE (mMLZE) increased in accordance with metastatic ability of B16 melanoma sublines. Human homolog of mMlze (hMlze) contained one leucine zipper structure and two potential nuclear localizing signals. Northern blot analysis of multiple human tissues showed that hMLZE was expressed primarily in trachea and spleen. We mapped the hMLZE gene (by fluorescence in situ hybridization) to 8q24.1 - 2, which contains the c-myc gene and is often amplified in malignant melanoma. Immunohistochemistry revealed that the number of hMlze-positive cases was significantly larger in Clark levels III, IV and V melanomas (6 / 11 = 55%) than in Clark levels I and II melanomas (2 / 15 = 13%). In two cases of hMlze-positive melanomas, the strength of hMlze staining increased substantially in the deep component of the tumor. Considering that melanomas above Clark level II are more metastatic than those below Clark level III, these findings suggested that MLZE is one of the genes whose expression is upregulated during the course of acquisition of metastatic potential in melanoma cells.     

血管生成拟态——肿瘤治疗的新靶点

在研究黑色素瘤过程中,Maniotis报道了一种独立于肿瘤血管生成的新的肿瘤微循环模式——血管生成拟态：强调它是无内皮细胞参与、细胞外基质界限的管道,肿瘤细胞沿管道外壁排列。Folberg等在脉络膜黑色素瘤中确认了血管生成拟态的7种PAS染色阳性管道模式,并归纳为二类．即中空的和实芯的PAS阳性网络结构。研究认为PAS染色阳性的血管生成拟态网状管道结构可能是肿瘤微循环的一种模式,不同于血管生成,也不同于肿瘤间充质反应。血管生成拟态现象的报道还见于乳腺癌、前列腺癌、卵巢癌、肺癌、胶质母细胞瘤、滑膜肉瘤、横纹肌肉瘤、嗜铬细胞瘤和细胞滋养层形成胎盘的过程。黑色素瘤细胞基因表达谱分析发现瘤细胞呈现遗传学失调和可塑性,其血管生成拟态调解过程中起重要作用的分子包括VE-cadhefin、EphA2、laminin5 γ2、MMPs、VEGF-C、LYVE1、TF、和NOTCH蛋白等。血管生成拟态概念的提出及其分子生物学调控机制的探讨为抗肿瘤治疗提供了新思路和可能的新靶点。     

Structure, Expression and Chromosome Mapping of MLZE, a Novel Gene Which Is Preferentially Expressed in Metastatic Melanoma Cells

We isolated a novel gene, termed MLZE , from a B16-BL6 cDNA library after subtraction of B16-F10 mRNA. Expression levels of mouse MLZE (mMLZE ) increased in accordance with metastatic ability of B16 melanoma sublines. Human homolog of mMlze (hMlze) contained one leucine zipper structure and two potential nuclear localizing signals. Northern blot analysis of multiple human tissues showed that h MLZE was expressed primarily in trachea and spleen. We mapped the h MLZE gene (by fluorescence in situ hybridization) to 8q24.1-2, which contains the c-myc gene and is often amplified in malignant melanoma. Immunohistochemistry revealed that the number of hMlze-positive cases was significantly larger in Clark levels III, IV and V melanomas (6/11=55%) than in Clark levels I and II melanomas (2/15=13%). In two cases of hMlze-positive melanomas, the strength of hMlze staining increased substantially in the deep component of the tumor. Considering that melanomas above Clark level II are more metastatic than those below Clark level III, these findings suggested that MLZE is one of the genes whose expression is upregulated during the course of acquisition of metastatic potential in melanoma cells.     

Co-Expression of Putative Cancer Stem Cell Markers,CD133 and Nestin,in Skin Tumors

Background: Cancer stem cells (CSC) are populations of cells responsible for tumor initiation, progression andtherapeutic resistance in many cancers. In the present study, we aimed to investigate the expression pattern andclinical significance of two CSC markers, CD133 and Nestin, in a series of skin tumors. Materials and Methods:One hundred and thirteen paraffin blocks from skin cancers including 16 (14%) cases of melanoma, 37 (33%)of squamous cell cancer (SCC) and 60 (53%) of basal cell cancer (BCC) were collected and assembled in a tissuemicroarray (TMA). The samples were immunohistochemically examined for the expression of CD133 and Nestin.Expression of these markers was also correlated with clinicopathological parameters. Results: A significantdifference was observed in the expression of CD133 and Nestin in melanomas, SCC and BCC (p value=0.001).Furthermore, the level of expression was significantly higher in the melanomas compared to the SCC and BCCtumors. Expression of CD133 in the melanoma was significantly associated with increased tumor invasiveness (pvalue=0.05), a higher rate of metastasis (p value=0.04) and the presence of ulceration (p value=0.02). Increasedexpression of Nestin was observed in metastatic melanoma (p value=0.04), while no statistically significantcorrelation was found with other clinicopathological parameters including Breslow thickness, Clark level andulceration. Conclusions: Elevated expression levels of CD133 and Nestin in the melanomas are associated withadvanced disease, with more aggressive and metastatic skin tumors. Therefore, these markers could be potentialtherapeutic targets for malignant tumors of the skin.     

Tumour-associated macrophage infiltration, neovascularization and aggressiveness in malignant melanoma: role of monocyte chemotactic protein-1 and vascular endothelial growth factor-A

The objective of this study was to evaluate the role of tumour-associated macrophages (TAMs) in malignant melanoma progression, invasion and angiogenesis. We examined the levels of macrophage infiltration and monocyte chemotactic protein-1 (MCP-1), neovascularization and vascular endothelial growth factor-A (VEGF-A) in different Clark's level melanomas with varying thicknesses and metastases. The level of TAM density was significantly higher in thick (>0.75 mm) than thin (0.75 mm) than thin (相似文献   

Macrophage infiltration correlates with tumor stage and angiogenesis in human malignant melanoma: possible involvement of TNFalpha and IL-1alpha

We examined whether macrophage infiltration is associated with angiogenesis in cutaneous melanoma. The numbers of macrophages and microvessels increased significantly with increasing depth of tumor and with tumor angiogenesis. Macrophage infiltration thus appeared to provide a useful diagnostic marker for the progression of cutaneous melanoma. We further examined whether human melanoma cells produce angiogenic factors in response to macrophage-derived cytokines, tumor necrosis factor alpha (TNFalpha) and interleukin-1 alpha (IL-1alpha). Treatment of melanoma cells with TNFalpha and IL-1alpha in vitro enhanced the production of interleukin-8 (IL-8) and vascular endothelial growth factor (VEGF), and of basic fibroblast growth factor (bFGF) to a lesser degree, in human melanoma cells. Lipopolysaccharide (LPS)-activated human monocytes enhanced production of IL-8, VEGF, TNF alpha, as well as IL-1alpha, but not bFGF. Co-culture of human monocytes and human melanoma cells was also found to significantly enhance production of IL-8 and VEGF in the absence and presence of LPS, compared with either monocytes or melanoma cells alone. The production of IL-8 and VEGF from co-cultured melanoma cells and LPS-activated monocytes was blocked when anti-TNF-alpha antibody or anti-IL-1alpha antibody was co-administrated. This is direct evidence that production of the potent angiogenic factors IL-8 and VEGF from melanoma cells is up-regulated through TNFalpha and/or IL-1alpha secreted by activated monocytes/macrophages, influencing both tumor growth and angiogenesis in melanomas.     

The contribution of bone marrow-derived cells to the tumor vasculature in neuroblastoma is matrix metalloproteinase-9 dependent

The contribution of the tumor stroma to cancer progression has been increasingly recognized. We had previously shown that in human neuroblastoma tumors orthotopically implanted in immunodeficient mice, stromal-derived matrix metalloproteinase-9 (MMP-9) contributes to the formation of a mature vasculature by promoting pericyte recruitment along endothelial cells. Here we show that MMP-9 is predominantly expressed by bone marrow-derived CD45-positive leukocytes. Using a series of bone marrow transplantation experiments in MMP-9(+/+) and MMP-9(-/-) mice xenotransplanted with human neuroblastoma tumors, we show that bone marrow-derived MMP-9 is critical for the recruitment of leukocytes from bone marrow into the tumor stroma and for the integration of bone marrow-derived endothelial cells into the tumor vasculature. Expression of MMP-9 by bone marrow-derived cells in the tumor stroma is also critical for the formation of a mature vasculature and coverage of endothelial cells with pericytes. Furthermore, in primary human neuroblastoma tumor specimens of unfavorable histology, we observed a higher level of tumor infiltration with MMP-9 expressing phagocytic cells and a higher degree of coverage of endothelial cells by pericytes when compared with tumor specimens with a favorable histology. Taken together, the data show that in neuroblastoma, MMP-9 plays a critical role in the recruitment of bone marrow-derived cells to the tumor microenvironment where they positively contribute to angiogenesis and tumor progression.