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Dalton Cardiovascular Research Center, Department of Biomedical Sciences, University of Missouri, 134 Research Park Drive, Columbia, Missouri 65211, USA

(Requests for offprints should be addressed to S M Hyder; Email: hyders{at}missouri.edu)

	Abstract

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
Angiogenesis is a key event, which occurs in both normal and pathological expansion of tissues and provides the nourishment necessary for growth. The role of angiogenic growth factors in breast pathology is rapidly gaining recognition since scientists and clinicians realized that these factors could function as molecular targets event 550 209822 for controlling tumor expansion. Vascular endothelial growth factor (VEGF) is a key regulator of angiogenesis. Although significant advances have been made in understanding the sex-steroid-dependent regulation of this key factor, the role of VEGF in controlling breast tumors is not well understood. In this review, I discuss recent studies describing the role of the female sex steroids estrogens and progestins in the regulation of VEGF in breast cancer cells. Furthermore, I present a summary of recent studies from other biological systems (mainly focused on tumor biology) directed towards providing us with a better understanding of the regulation of classical VEGF and VEGF receptors. I propose that by extending such studies we will gain deeper insights into how we might combat the progression of breast cancer by controlling hormone-dependent angiogenesis within tumor tissue. I believe that information gained from such studies will permit us to target angiogenic growth factors and their initiated signal transduction pathways in a more precise and selective manner, and thereby to control the formation of new blood vessels that fuel the rapid growth of breast tumors. Finally, it is my hope that the concepts discussed here will help elucidate molecular targets in the hormone-dependent angiogenesis pathway that will ultimately allow us to overcome anti-hormone resistance and to provide insights into how we might pursue the concept of chemoprevention by considering ‘angioprevention’ as the end point.

	Introduction

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
A key function of the vasculature is to provide a nutrient supply to the organ and, in most species, three major types of regulation occur: vasodilation, changes in capillary permeability, and growth and development of new vessels, also known as angiogenesis (Folkman 2003, Hoeben et al. 2004, Carmeliet 2005). At the beginning of the 20th century, it was recognized in females that vasculature changes occurring in the reproductive tract were under the control of ovarian hormones. Since then, most studies have concentrated on developing our understanding of the role played by sex steroids in angiogenesis in uterine and ovarian tissue since there is evidence that neovascularization is influenced by ovarian steroids in these tissues (Findlay 1986, Reynolds et al. 1992, Brenner & Slayden 1994, Hyder & Stancel 1999, Augustin 2005). In most other adult tissues angiogenesis is a quiescent process. Since it was recognized that tumor expansion, irrespective of tissue origin, depends on the process of angiogenesis (Goldberg & Rosen 1997), a greater interest has been taken in the role of angiogenic growth factors. Expansion of many endocrine-dependent cancers, including many breast tumors, depends on sex steroids; consequently, there has been a recent upsurge in efforts to understand the role of these steroids in controlling both angiogenic and anti-angiogenic factors in normal and neoplastic breast tissue and cells. In the United States alone, about 200 000 new cases of breast cancer are detected annually and approximately 40 000 women die each year of this deadly disease. Endocrine therapy is the choice of treatment for those tumors that possess estrogen or progesterone receptors (ER or PR). However, many tumors either do not respond to this form of treatment or, after initially responding to treatment, go on to develop a population of cells that become resistant and therefore unresponsive to anti-hormone treatment. Alternate methods of treatment include chemotherapy or the use of aromatase inhibitors (Kaklamani and Gradishar 2005, Navolanic & McCubrey 2005). It is only recently that strong scientific evidence has been acquired proving that breast cancer is an angiogenic-dependent disease, which is potentially treatable by anti-angiogenic therapy (Longo et al. 2002, Atqur-Rehman & Toi 2003, Morabito et al. 2004, Moses et al. 2004, Ferrara & Kerbel 2005, Schneider & Miller 2005). Since the presence of both ER and PR influences the progression of the disease, it has been suggested that these receptors must be controlling angiogenic factors via their respective ligands (Hyder & Stancel 1999, 2000). Thus, studying the control of growth factors by sex steroids provides an area with important potential, since we may well be able to identify possible targets for anti-angiogenic therapy and control the disease before endocrine resistance develops. Furthermore, anti-hormones might also be modifying or inducing angiogenic inhibitors and thereby controlling tumor growth. These molecular targets representing components of the angiogenic pathway in breast cancer could be used for chemoprevention or for controlling tumor expansion. In this review, I will concentrate on evidence that breast cancer is an angiogenic-dependent disease and discuss the role of sex steroids (estrogens and progestins) in controlling the production of angiogenic growth factors. While several such vascular growth factors have been identified in breast cancer cells, which could influence cell growth, my discussion will concentrate on one of the most potent, termed vascular endothelial growth factor (VEGF). VEGF and its isoforms, in concert with specific receptors, comprise one of the most potent angiogenesis-promoting loops yet identified that significantly promotes tumor expansion (Rak et al. 1996, Saaristo et al. 2000, Zhang et al. 2000a, 2002, Huh et al. 2004). Consequently, VEGF represents a molecular target with immense therapeutic potential and I will focus on the role of estrogens and progestins in controlling production of VEGF in breast cancer cells. Finally, I will discuss the potential targets and strategies aimed at controlling the process of angiogenesis and curtailing this deadly disease.

	Angiogenesis in breast cancer

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
Angiogenesis is the process by which new capillaries are generated from existing vessels. During embryonic development, the formation of a primary vascular plexus (vasculogenesis) occurs from angioblasts, primitive blood vessels are formed and extensive angiogenesis then occurs by sprouting and branching (Risau 1997, Carmeliet 2005). In the adult organism, angiogenesis is limited to relatively few tissues including the ovary and uterus, but the formation of new vessels commonly occurs during tumor growth (Goldberg & Rosen 1997, Zetter 1998) and in a number of other diseases (Folkman 1995). Ovarian hormones may influence angiogenesis in breast tissue, but the details of how such a process occurs under normal physiological situations remains obscure.

Whether it occurs during development, normal physiological processes, or in pathological conditions, angiogenesis is an extremely complex process. New capillaries originate from a pre-existing microvasculature which consists mainly of capillaries and venules, rather than from larger vessels with a smooth muscle layer. One of the initial events that occurs in response to an angiogenic stimulus is an increase in capillary permeability (Dvorak et al. 1995). This allows fibrinogen and other serum proteins to exit the capillary space and form an extravascular fibrin gel. This matrix then supports the in-growth of endothelial cells and other elements to generate new vascularized stroma. For additional information on mechanisms of angiogenesis, interested readers are referred to several recent reviews about the basic process of angiogenesis (Goldberg & Rosen 1997, Zetter 1998, Nicosia & Villaschi 1999, Carmeliet 2005).

There is now considerable evidence that breast cancer is an angiogenic-dependent disease and that angiogenesis plays an essential role in breast cancer development, invasion, and metastasis (Lichtenbeld et al. 1998, Dabrosin et al. 2003b, Schneider & Miller 2005). Even though it has been recognized for decades that breast cancer is an endocrine-dependent disease, little attention has been paid to the role of sex steroids in the process of angiogenesis in breast cancer cells. Since breast tissue is a target for sex steroids and many breast tumors are hormone responsive, it is very likely that sex steroids control the production of angiogenic growth factors or help in the removal of factors, e.g. anti-angiogenic proteins that impede the process. Strong evidence that breast cancer is an angiogenesis-dependent disease comes from hyperplastic murine breast papillomas (Brem et al. 1977) and histologically normal lobules adjacent to cancerous breast tissue that possess higher levels of blood vessels (Jensen et al. 1982), suggesting that angiogenesis precedes transformation of mammary hyperplasia to malignancy (Gimbrone & Gullino 1976, Maiorana & Gullino 1978). In addition, transfection of breast cancer cells with angiogenic stimulatory peptides increases tumor growth, invasiveness, and metastasis (Zhang et al. 1995, 2000a). Conversely, transfection of tumor cells with inhibitors of angiogenesis decreases growth and metastasis (Sledge & Miller 2003). It has been suggested that tumor progression occurs once the balance is attained that favors angiogenic activators over inhibitors of angiogenesis and a number of factors have been shown to alter from a pre-invasive to an invasive status within breast tumors (Folkman & Hanahan 1991, Engels et al. 1997a,b). This could involve either the induction of angiogenic growth factors (e.g. VEGF, fibroblast growth factor (FGF), matrix metalloproteinases, etc.) or the loss of inhibitors of angiogenesis such as thrombospondin-1 (TSP-1), soluble (s)VEGF receptors and tissue inhibitor of metalloproteinases, etc. Several factors such as hypoxia or loss of tumor suppressors and angiogenesis inhibitors can disrupt the angiogenic balance in a tissue leaning towards tumor progression. This is commonly referred to as an angiogenic switch and describes the sudden growth of tissues that otherwise remain quiescent for a long time (Folkman & Hanahan 1991, Bos et al. 2001, Bergers & Benjamin 2003, Naumov et al. 2006), as occurs in many human breast tumors. The effect of sex steroids on the angiogenic switch remains to be determined; however, the interest to find a connection has gained momentum over the past few years since modulation of this switch could prove crucial in preventing the progression of breast cancer.

There are several clinicopathologic conditions that also confirm the central role of angiogenesis in breast cancer progression. It has been shown, for example, that fibrocystic lesions with the highest vascular density are associated with a greater risk of breast cancer (Guinebretiere et al. 1994). Similarly, microvessel density (MVD) was shown to be highest with histopathologically aggressive ductal carcinoma in situ lesions (Guidi et al. 1994) and was associated with increased VEGF expression (Guidi et al. 1997). High MVD in premalignant lesions has been associated with high risk of future breast cancer (Guinebretiere et al. 1994). Also, high MVD in invasive disease correlates with a greater likelihood of metastatic disease (Weidner et al. 1991), shorter relapse-free intervals and reduced overall survival in patients with node-negative breast cancer (Weidner et al. 1992). A number of angiogenic factors are commonly expressed by invasive human breast cancers (Engels et al. 1997a,b, de Jong et al. 1998), VEGF 165 and VEGF 121–amino acid isoforms being the most predominant (Relf et al. 1997). VEGF expression has also been found to correlate with risk and outcomes in breast cancer (Linderholm et al. 2000a, 2001). Carriers of the C936T allele in the VEGF gene were more frequent among controls than among a cohort of breast cancer patients, implying a protective effect for carriers of the variant polymorphism (Krippl et al. 2003) and even improved metastasis-free survival time in patients with low-grade breast cancer (Krippl et al. 2004). Several studies found an inverse correlation between VEGF expression and overall survival in both node-positive and node-negative breast cancer (Gasparini 1997, 2000, Gasparini et al. 1999, 2005, Linderholm et al. 2000b). Increased VEGF and VEGF receptor expression is also associated with impaired response to tamoxifen or chemotherapy in patients with advanced breast cancer (Foekens et al. 2001, Ryden et al. 2005). Recently, VEGF and VEGF receptor expression has been successfully quantified via immunohistochemistry in breast cancer tumor specimens (Ragaz et al. 2004), the expression and intensity of expression correlating with a significantly inferior clinical outcome (Meunier-Carpentier et al. 2005).

One of the key features of VEGF is that it can promote permeability in tissues resulting in hyperemia (Dvorak et al. 1995). There is evidence that hormone replacement therapy increases breast tissue density and it is possible that some of these effects arise due to the hyperemic effects of estrogens via the production of VEGF, which may become more pronounced with the inclusion of progestins (Noh et al. 2005). Indeed, recent evidence suggests that progesterone may have effects on breast vaculature (Thomas et al. 2003). Thus, it is likely that both estrogens and progestins have direct effects on both normal and neoplastic cells as well as the resident endothelial cells, via their respective receptors. In addition, there is a possibility that a paracrine mechanism exists that could also arise from the production of angiogenic growth factors in breast tissue following hormonal treatment. It has been proposed that such paracrine mechanisms might even allow proliferation of tumor cells that lack the capacity to produce their own angiogenic growth factors in response to steroid hormones but which respond to VEGF produced from other cells, since they may retain the necessary cell-surface receptors (Liang & Hyder 2005). Further research is required to establish if such regulatory loops occur in vivo, although recent reports indicate the possibility that this process may operate in real clinical conditions. Thus, targeting both the angiogenic ligand and the receptors would seem to be the most comprehensive strategy for better controlling tumor proliferation.

Angiogenic growth factors in breast cancer

Given the complexity of angiogenesis, it is not surprising that a large number of factors have been identified that can stimulate or inhibit this process (Goldberg & Rosen 1997, Zetter 1998, Ferrara 1999, Nicosia & Villaschi 1999). However, we still do not know the overall extent of various angiogenic growth factors produced by malignant breast cells and whether there is a master regulator that should be targeted for therapy. Recent research has shown that indeed breast cancer cells and breast cancer biopsies do exhibit several angiogenic growth factors (Engels et al. 1997a,b, de Jong et al. 1998). One should be cautious when investigating ‘angiogenesis’ and angiogenic growth factors, since it is entirely possible that angiogenesis may proceed with no change per se in the levels of pro-angiogenic growth factors. However, the production of angiogenesis inhibitors may be blocked, or receptors for angiogenic growth or inhibitory factors may be reduced, as recently described in estrogen-dependent stimulation of angiogenesis in breast cancer (Elkin et al. 2004). In this case, sVEGFR-1, which binds and neutralizes the actions of VEGF, is decreased, thus creating a more favorable angiogenic environment for tumor progression. Despite this complexity, two factors emerging as key regulators of angiogenesis in most systems are VEGF (Ferrara 2005, Hicklin & Ellis 2005) and basic fibroblast growth factor (bFGF) (Cronauer et al. 1997, Yazidi et al. 1998). The detailed effects of sex steroids on bFGF in breast cancer cells remain to be elucidated; consequently, this review will concentrate on VEGF and its receptors, which, to date, have received most attention from endocrinologists, especially since recent clinical trials have shown it to be a good candidate for anti-angiogenic therapy (Ferrara et al. 2005, Jain et al. 2006). However, readers should be aware that other angiogenic proteins exist which play a role in breast cancer, although their modulation by steroid hormones is poorly understood. These include, but are not limited to, insulin-like growth factor-I and its receptor (Kucab & Dunn 2003) and interleukin-8, which is regulated by estrogen in breast cancer cells (De Larco et al. 2001, Lin et al. 2004).

	VEGF and vascular permeability factor

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
VEGF is a multi-functional cytokine, originally identified as a protein produced by tumor cells that increased the permeability of capillaries to proteins (Dvorak et al. 1995, Ferrara et al. 2003a). It was subsequently discovered to be selectively mitogenic for endothelial cells and to stimulate angiogenesis (Ferrara & Davis-Smyth 1997, Ferrara 1999). This factor has been referred to in the literature as vascular permeability factor (VPF), VEGF, or vasculotropin. VEGF is expressed in both epithelial and mesenchymal cells in a wide variety of tissues, and it is highly expressed in many tumors, including breast cancers (Goldberg & Rosen 1997, Ferrara 1999, Neufeld et al. 1999, Ferrara et al. 2004a,b, Carmeliet 2005, Hicklin & Ellis 2005).

Both the human and murine VEGF genes contain eight exons and seven introns, and differential exon splicing generates up to six isoforms of VEGF (Neufeld et al. 1999). The best characterized are the four predominant human forms, containing 121, 165, 189 and 206 amino acids, and corresponding forms with one fewer amino acid in the mouse (Ferrara 1999). In most systems, VEGF 121 and VEGF 165 are the major species expressed. VEGF 206 is not predicted for rodents due to an inframe stop codon resulting in the loss of one amino acid. VEGF 165 lacks exon 6, VEGF 121 lacks exons 6 and 7, VEGF 189 has an insertion of 24 amino acids in the VEGF 165 sequence and VEGF 206 contains an additional insertion of 17 amino acids. A major difference between the different forms of VEGF is their heparin-binding capability. VEGF 121 is freely diffusible, but the other major forms contain heparin-binding regions that can mediate binding to cell surfaces and the extracellular matrix, and thus provide a potential reservoir for locally controlled release by heparinases or plasmin (see Ferrara & Davis-Smyth 1997). VEGF 165, the major isoform, is a basic homodimeric protein of 45 kDa which binds heparin. It is interesting that loss of heparin-binding ability leads to a loss of mitogenic activity indicating that the proteolytically released fractions may have other unknown functions (Ferrara & Davis-Smyth 1997).

The promoter for human VEGF has been extensively analyzed (Ferrara 1999, Pages & Pouyssegur 2005). It contains one major start site near a cluster of Sp1-binding sites. In the vicinity of the promoter, there are also a number of putative AP1 and AP2 elements. In contrast to the human gene, the 3'-untranslated region of the rat gene has been extensively explored. There are four potential polyadenylation sites and the one most frequently used is 1.9 kb downstream of the translation termination codon. Interestingly, the sequence in the 3'-untranslated region contains a number of regions that are known to be involved in regulating the stability of mRNA. From the point of view of this review, both functional estrogen and progesterone responsive regions have been located in the VEGF gene (Hyder et al. 2000a, Mueller et al. 2000, 2003, Buteau-Lozano et al. 2002, Stoner et al. 2004, Wu et al. 2005a). Interestingly, a recent study using the chromatin immunoprecipitation procedure reports additional ER sites on the rat VEGF promoter and suggests that these mediate the estrogen response (Kazi et al. 2005). However, in our studies, we have found that not all sites that bind steroid receptors (as demonstrated by chromatin immunoprecipitation studies or using gel shift assays) are necessarily functionally active (Hyder et al. 1995, J Wu & SM Hyder, unpublished data). Thus, receptors may have additional functions yet to be determined on the VEGF promoter. Further studies are needed to confirm the exact locations of functional ER-and PR-binding sites on the VEGF promoter, although irrespective of their location, both hormones have a profound effect on VEGF induction, especially in the uterus (Cullinan-Bove & Koos 1993, Hyder et al. 1996). Their effects in breast cells are controversial as will be discussed below.

A number of VEGF-related genes referred to as VEGF B, C, D, E, and placental growth factor have been identified (Eriksson & Alitalo 1999, Meyer et al. 1999). Some of these forms may have selectivity for certain functions, e.g. VEGF C may be the factor that regulates capillary growth in the lymphatic system (Jeltsch et al. 1997). In addition, since VEGF binds to its receptor as a dimer (see below), the various VEGFs can form heterodimers, either with variants of the same family or with the members of another family that may have different activities. Interestingly, there are recent reports of a naturally occurring VEGF isoform, termed VEGF 165b, that is a negative regulator of cellular functions promoted by VEGF 165, including angiogenesis (Woolard et al. 2004). VEGF 165b has the same number of amino acids as VEGF 165 but six amino acids in the COOH terminal region usually coded for by exon 8 are different. The COOH terminal of VEGF 165 is necessary for determining mitogenic signaling, therefore changes in this region are believed to influence its functions. The new open reading frame is termed exon 9 (Woolard et al. 2004). Unlike the other VEGF isoforms, which stimulate angiogenesis, VEGF 165b is an endogenous inhibitory form of VEGF, which decreases VEGF-induced proliferation and migration of endothelial cells. Although it can bind to VEGFR-2 (Flk-1/KDR), VEGF 165b binding does not result in receptor phosphorylation or activation of downstream signaling pathways (Woolard et al. 2004). No information is available on the regulation of VEGF 165b by sex steroids, and the presence and role of VEGF 165b in breast cancer remains to be established. Since VEGF 165b may be an important player in both tumor angiogenesis as well as normal tissues, there is an urgent need to confirm the early reports by other investigators.

Regulation of VEGF is under both transcriptional and translational control (Akiri et al. 1998). While sex steroids have been shown to induce transcription of the VEGF gene (Hyder et al. 1996, 2001), the effect of hormones on post-transcriptional regulation of VEGF in breast cancer cells remains to be explored. Recent studies, however, suggest that a post-transcriptional event is indeed likely (Wu et al. 2004, 2005b). There may be several points of interaction between sex steroids and VEGF regulation and I will briefly review those factors that may be important for future consideration in the field of breast cancer. Hypoxia, one of the most potent inducers of VEGF mRNA synthesis, induces a powerful transcriptional activator, hypoxia-inducible factor (HIF)-1, which binds to a hypoxia-responsive region on the VEGF promoter and induces gene transcription (Hicklin & Ellis 2005). HIF-1 is upregulated in breast cancer and serves as a prognostic factor (Bos et al. 2001, 2005). It has been suggested that estrogens may involve the HIF transcription factor for VEGF induction in uterine cells (Kazi et al. 2005). However, hypoxia has been shown to reduce ER and ER function in breast cancer cells (Kurebayashi et al. 2001), clouding the issue of the role of HIF in ER function in the uterus, although it is possible that HIF effects may be tissue specific. VEGF is also regulated by several growth factors and cytokines, as well as oncogenes and tumor suppressor genes (Rak et al. 1995, Hicklin & Ellis 2005), many of which are frequently observed in breast cancer. Much focus has centered on the role of tumor suppressor p53 in VEGF regulation since elevated levels of VEGF promote tumor progression and p53 is implicated in the molecular pathology of many solid malignancies. It has been shown that direct interaction of the p53 protein with the transcription factor Sp1 prevents transcriptional activation of the VEGF promoter in breast cancer cells (Pal et al. 1998, 2001, Milanini-Mongiat et al. 2002). Several studies have also shown that genetic alterations of tumor suppressor genes, such as p53, can lead to induction of additional factors such as HIF-1 (Blagosklonny et al. 1998), leading to increased VEGF production and angiogenesis. Similarly, we recently discovered that loss of wtp53 allows PR to induce VEGF in breast cancer cells (Liang et al. 2005). This novel observation is further strengthened by the fact that transfection of wtp53 into breast cancer cells expressing mtp53 can suppress progesterone-dependent VEGF release from tumor cells (Liang et al. 2005). However, it remains to be established how steroid receptors interact with p53 and the VEGF promoter. Elucidation of these mechanisms is essential if we are to better understand the role of p53 in the induction of angiogenically active VEGF.

The post-transcriptional regulation of VEGF is a well-studied area of research. A protein known as eukaryotic initiation factor 4E (eIF4E) plays a major role in the translation of VEGF mRNA (Kevil et al. 1996). eIF4E, a 25 kDa mRNA cap-binding phosphoprotein, is the rate-limiting factor responsible for delivering cellular mRNAs to the eIF4F complex that facilitates ribosome loading and mRNA translation (Mamane et al. 2004). eIF4E has been shown to be upregulated in many tumors with an associated increase in VEGF message (Nathan et al. 1997, De Fatta et al. 1999). The role of sex steroids in controlling the translational factors that control angiogenic growth factors remains to be determined.

VEGF receptors

Receptors for VEGF are members of the tyrosine kinase family and were initially identified on endothelial cells (Hicklin & Ellis 2005). Subsequently, they have also been observed on non-endothelial cells, including epithelial and stromal cell types of breast cancers (Speirs & Atkin 1999, Nakopoulou et al. 2002, Liang & Hyder 2005), although reports are limited regarding the role and regulation of VEGF receptors by sex steroids in breast cancer cells. It should be noted that VEGF receptors have been shown to function differentially (Hicklin & Ellis 2005), implying that if differential regulation by sex steroids occurs, then it is likely that different functions can be assigned to VEGF receptors during hormone-induced proliferation of breast cancers. Readers are referred to several excellent reviews for a detailed summary of our understanding of VEGF receptors (Eriksson & Alitalo 1999, Neufeld et al. 1999, Ortega et al. 1999, Hicklin & Ellis 2005). A discussion of some of the salient points follows.

There are three members of the VEGF receptor family: VEGFR-1 (Flt), VEGFR-2 (flk/KDR), and VEGFR-3 (Flt4). All three are receptor-type tyrosine kinases, which are expressed primarily, though not exclusively, by endothelial cells. The first two bind the classical VEGF (VEGF A) and the latter interacts with VEGF C and D. At present, the mitogenic actions of VEGF are thought to be mediated primarily by VEGFR-2. Several other forms of VEGF receptors have been identified, but their physiological functions have not been well established (see Neufeld et al. 1999, Ortega et al. 1999, Hicklin & Ellis 2005).

VEGF receptors are crucial for embryonic development. VEGFR-1 binds the ligand with a greater affinity than VGEFR-2. An alternatively spliced form of VEGFR-1, lacking the seventh immunoglobin-like structure and both the transmembrane and cytoplasmic domains, has been identified in HUVEC cells. Since this receptor binds VEGF with high affinity and prevents VEGF-induced mitogenesis, it may represent a negative regulator of angiogenesis. Autoradiographic studies have localized these receptors to both proliferating and quiescent endothelia. Gene knockout studies indicate that the two receptors exhibit different functions in vivo and several biochemical studies have shown that flk but not flt is responsible for mediating the mitogenic signal within endothelial cells. VEGF receptors have diverse biological roles, including cell proliferation, migration, vascular permeability, induction of protease activity, and in vitro angiogenesis. Recently, neuropilin, the neuronal cell guidance receptor for the semaphorin ligands, has also been identified as a VEGF receptor (Hicklin & Ellis 2005). This receptor binds VEGF 165 specifically but because of its short intracellular domain it is unlikely to function as an independent receptor. This assumption is based on the fact that when expressed alone this receptor is unable to modulate responses to VEGF 165, but neuropilin can influence VEGF 165 binding to its other receptors. Neuropilin may thus represent a co-receptor for VEGF 165. It is interesting to note that several non-endothelial cell types express neuropilin and many breast and prostate cancer cell lines have abundant amounts of this receptor. The role of neuropilin and its regulation by sex steroids is poorly understood, both in prostate and breast cancer cells and requires further analysis.

Limited information is available on the signal transduction mechanisms for VEGF receptors and, apart from a few cases, selected binding of downstream signaling molecules to one or the other receptor has not been demonstrated. A number of proteins are phosphorylated following the interaction of VEGF with its receptors. Occupancy of VEGF receptors leads to autophosphorylation as well as phosphorylation of other effectors, including phospholipase C, the GTPase activating protein Ras-GAP and the adaptor proteins Nck and Shc. Also, both receptors possess the Grb2-binding site. Both Grb2 and Shc could potentially induce the Ras pathway; however, the involvement of Ras in the VEGFR signaling pathway has not been established.

Following receptor activation in endothelial cells, a number of cellular responses occur that are likely to play a role in angiogenesis and tissue remodeling, e.g. induction of urokinase and urokinase receptors, tissue plasminogen activators (PA), PA inhibitors, metalloproteinase activity, vascular cell adhesion molecule-1 and intercellular adhesion molecule-1 expression, and hexose transport (Pekala et al. 1990, Ferrara 1999). Special note should be made of VEGFs’ ability to induce fenestrations in capillaries in vivo (Roberts & Palade 1995), which is reminiscent of estrogenic effects in the female rodent reproductive tract (Martin et al. 1973). Whether such effects occur in the mammary gland remains to be determined, although they would provide a probable explanation for the increased breast density seen following hormone replacement therapy (HRT) (Colacurci et al. 2001, Erel et al. 2001). If such an effect can be shown in the breast, it may explain breast tenderness and increased mammographic density, which occur as a result of HRT.

Several important differences have recently been reported between the two VEGF receptors (reviewed in Hicklin & Ellis 2005). For example, when VEGFR-2 is expressed in cells and exposed to ligand, a strong ligand-dependent tyrosine phosphorylation of the receptor occurs. In contrast, VEGFR-1 does not show such an intense signal. It is therefore possible that the intense signal, which occurs with VEGFR-2, may be required for eliciting a full response spectrum for mitogenic events to occur. VEGFR-1 has been shown to interact with the p85 subunit of phosphatidyl inositol 3-kinase implicating higher levels of phosphatidyl inositol involvement in cell signaling pathways, although it is not known whether this is a receptor selective effect. VEGFR-2 has been shown to associate with the protein tyrosine phosphatases SHP1 and 2 suggesting that these two proteins may be involved in some form of signal modulation. However, it is not known if these proteins also interact with VEGFR-1. It has been shown that the immigration of monocytes in response to VEGF only occurs through VEGFR-1-induced signaling (Barleon et al. 1996). Most interestingly, VEGF-treated cells containing VEGFR-1 have been shown to contain the phosphorylated Src family members, fyn and yes. These proteins, however, are not phosphorylated in VEGFR-2-containing cells, indicating that subtle differences may exist in the signal transduction pathways of these two receptors. The role of VEGF receptors in breast cancer remains to be explored since it is likely that they affect processes such as angiogenesis, tumor cell motility, invasion, survival and metastasis. Emerging evidence supports such roles (Price et al. 2001, Nakopoulou et al. 2002, Ryden et al. 2003, Wedam et al. 2006).

	Sex-steroid regulation of VEGF and VEGF receptors in breast cancer

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
As discussed earlier, it is now well established that breast cancer is an angiogenic-dependent disease and that the level of angiogenesis in a tumor serves as an independent prognostic indicator for tumor growth, response to therapy and clinical outcome (Gasparini 1997, 2000, Gasparini et al. 2005). Importantly, both VEGF and its receptors are overexpressed in many breast tumors, and interested readers are referred to several recent articles and reviews which cover this topic in detail (Toi et al. 1994, 1995a, Toi et al. b, Brown et al. 1995, Anan et al. 1996, Yamamoto et al. 1996, Guidi et al. 1997, de Jong et al. 1998, Lee et al. 1998, Linderholm et al. 1998, McLeskey et al. 1998, Ryden et al. 2005). The data with respect to the effects of estrogens on regulation of VEGF and its receptors in breast cancer are emerging in the literature, although a clear picture is still not available (Hyder & Stancel 2000, Elkin et al. 2004). Limited data are, however, available on the regulation of VEGF and its receptors by progestins in breast cancer. There is now considerable evidence that, compared with women treated with estrogens or placebo, those undergoing HRT containing a progestin component, develop tumors more readily (Ross et al. 2000, Writing Group for Women’s Health 2002, Chlebowski et al. 2003), leading to renewed interest in the role of progesterone in breast cancer (Moore 2004). It is possible that human tumors may expand under the influence of progestins, and in rodents progestins have been shown to be associated with tumor expansion (Pasqualini 2000, Lanari & Molinolo 2002, Schairer 2002, Connelly et al. 2003).

Given the importance of estrogens and progestins in the regulation of breast cancer, and the clear evidence that angiogenesis plays an important role in the onset, progression and metastasis of this disease, it is surprising that so few studies have examined the regulation of VEGF by sex steroids in this context. This is clearly an important area for further study, especially since many reports show that these hormones regulate VEGF expression in normal estrogen and progestin target tissues (Cullinan-Bove & Koos 1993, Hyder et al. 1996, 2001, Hyder & Stancel 1999).

Estrogen regulation of VEGF and VEGF receptors in breast cancer cells

Recent studies have shown that VEGF acts as a growth stimulator and a proliferation factor for mammary cancer cells (e.g. Liang & Hyder 2005, Schoeffner et al. 2005). In addition, it has been shown that estrogens can regulate VEGF in mammary and uterine cells (Hyder et al. 1996, Nakamura et al. 1996, 1999) and that the proliferation rate of the breast epithelium peaks in the luteal phase of the menstrual cycle (Anderson et al. 1982, Soderqvist et al. 1997). Taken together, these findings suggest that estradiol in combination with progesterone likely stimulates the proliferation rate of breast cells and potentially might also promote angiogenesis in the normal and neoplastic breast tissue accompanying the steroid-dependent increase in tissue mass (as recently discussed in prostate) (Folkman 1998).

While it has been shown that many human breast cancers are under hormonal regulation, data are surprisingly limited regarding the regulation of VEGF and its receptors by sex-steroid hormones in breast cancer. Zhang et al.(1995) observed that MCF-7 cells transfected with a VEGF 121 expression vector grew much faster, formed tumors more rapidly, and were more angiogenic when implanted into nude mice supplemented with estradiol, compared with non-transfected MCF-7 cells. Similarly, Brodie’s group (Nakamura et al. 1996) showed that estradiol regulates the expression of VEGF in estrogen-responsive 7,12-dimethyl-1,2-benz[a]anthracene (DMBA)-induced rat mammary tumors, and the levels of extracellular VEGF have been shown to increase in response to estradiol in murine mammary cancer cells (Dabrosin et al. 2003a). Garvin et al.(2005) showed that estradiol elevated VEGF levels in human breast cancer cells while simultaneously decreasing sVEGFR-1, thus increasing the angiogenic milieu. The latter effects were suppressed by tamoxifen. An estrogen-responsive element in both the rat and human VEGF gene has been identified (Hyder et al. 2000a, Mueller et al. 2000, Buteau-Lozano et al. 2002, Stoner et al. 2004) that interacts with both ER and ERß. While estrogens consistently induce VEGF at transcriptional levels in uterine tissue in a receptor-dependent manner (Hyder et al. 1996, 1997), and the gene contains an estrogen responsive region, the response is not so robust in human breast cancer cells (Hyder et al. 1998). In fact, a number of investigators have failed to demonstrate such an effect; others show only a modest response (Hyder et al. 1998, 2001, Ruhola et al. 1999, Bermont et al. 2001, Buteau-Lozano et al. 2002, Stevens et al. 2003, Mirkin et al. 2005), and even inhibition of VEGF mRNA by estradiol in breast cancer cells has been reported (Bogin & Degani 2002), although the latter results should be interpreted with caution since very high levels of estradiol were used (30 nM) and only a semi-quantitative method was utilized to reach this conclusion. It has also been reported using transient transfection assays that ERß represses VEGF promoter in breast cancer cells, although whether such an effect occurs in a cell line that expresses high levels of ERß remains to be determined (Buteau-Lozano et al. 2002). Sengupta et al.(2003) provide evidence that induction of VEGF by estradiol in MCF-7 breast cancer cells is a biphasic event, with increases in VEGF message at 2 and 24 h post-estrogen treatment, although not 6 h after estrogen administration. However, a biphasic effect is not observed in an in vivo DMBA-induced mammary tumor model, in which VEGF induction occurs by 2 h in response to estradiol and reaches a peak after 6–8 h, before declining by 24–48 h (Nakamura et al. 1996). It is likely that wide variations in in vitro VEGF induction within breast cancer cells will arise as a consequence of different lengths of exposure to the hormone, variations in hormone concentration used and alterations in cellular characteristics (e.g. endogenous transcription factor levels) which might occur due to various growth conditions used for cells in culture (Hyder 2002). It has been proposed that HIF- may influence estrogen-dependent increases in VEGF message in the rat uterus (Kazi et al. 2005). A similar mechanism may exist in breast cancer cells and fluctuation of such factors (or ER itself) may dictate estrogen-dependent VEGF induction (Coradini et al. 2004). Interestingly, studies suggest that post-transcriptional events might also influence estrogen-dependent release of VEGF from human breast cancer cells, an effect that is suppressed by tamoxifen (even though tamoxifen increases both mRNA and protein levels of VEGF in MCF-7 cells). This may explain why tamoxifen causes regression of ER-containing tumors (Garvin & Dabrosin 2003), while at the same time actually increasing VEGF levels in certain breast cancer cells (Ruhola et al. 1999, Wu et al. 2004). A recent study showed that estrogen acts as an angiogenic switch in breast cancer cells by downregulating soluble VEGFR-1 (s-flt) which is believed to sequester available VEGF, although whether this is a direct or an indirect effect of hormone remains to be determined (Elkin et al. 2004, Garvin et al. 2005). It has been suggested that loss of s-flt provides an increase in the net balance towards estrogen-dependent angiogenesis in breast cancer cells.

In contrast to what we know regarding the role of sex steroids in controlling VEGF and angiogenesis in cancer cells, little is known about how angiogenesis is regulated in normal human breast tissue. VEGF mRNA levels were found to be increased in the mammary gland of baboons in the luteal phase of the cycle, when estradiol and progesterone levels are elevated (Greb et al. 1997). Dabrosin (2003, 2005b) showed that in healthy women, bio-available VEGF levels fluctuate in normal human breast tissue during the same (luteal) phase of the menstrual cycle, when estradiol and progesterone levels are high; local extracellular levels of VEGF in the breast were doubled compared with the follicular phase, while plasma levels of VEGF did not show a cyclic variation. These results suggest that sex steroids affect VEGF production in normal breast tissue, although it is not yet clear whether this is an effect of estradiol alone or whether progesterone is also involved. Addition of progesterone to estradiol in tissue culture experiments with normal breast biopsies did not alter the estrogen-induced VEGF levels (Dabrosin 2005b). Importantly, it has not been proven whether VEGF in the normal breast can be associated with the initiation or progression of tumors. Other evidence that sex steroids may regulate VEGF in the breast comes from observations that premenstrual breast tenderness and edema is a common symptom in women and studies suggest that VEGF may be involved in mechanisms that cause premenstrual mastalgia (Ader et al. 2001).

Progestin regulation of VEGF and VEGF receptors in breast cancer cells

As is the case with estrogen, the effects of progesterone on angiogenesis and VEGF expression in breast cancer are poorly understood. Consequently, we have scant information concerning the possible role of progesterone and its synthetic derivatives on angiogenesis and/or regulation of VEGF. Both animal studies and human clinical trials indicate a role for progestins in increasing the risk of breast cancer (Ross et al. 2000, Writing Group for Women’s Health 2002, Chlebowski et al. 2003, Chen et al. 2004). Recent epidemiological trials have rejuvenated the interest of the scientific community and there is an impetus to better understand the role of synthetic progestins in breast cancer, particularly in the area of progestin induction of angiogenic growth factors, which likely leads to tumor expansion (Hyder et al. 2001). Since many progestins have biological activities which differ from the natural hormone, studies are underway to better understand the role of various synthetic derivatives in regulating angiogenic growth factors in breast cancer cells. A connection between possible direct regulation of VEGF expression by progesterone was first described by Cullinan-Bove and Koos (1993) in the rat uterus and a role of progesterone in expansion of mammary tumors has been described (reviewed in Lanari & Molinolo 2002). We investigated the role of this class of hormone in angiogenic growth factor regulation in breast cancer. We showed that both natural and synthetic progestins used in HRT induced VEGF in breast cancer cells (Hyder et al. 1998, 2001, Liang et al. 2005), observations which have since been confirmed by other investigators (Mirkin et al. 2005). Progesterone response elements have been identified on the human VEGF promoter although it seems that the VEGF promoter is utilized in a cell-specific manner and different regions are involved in directing VEGF synthesis (Mueller et al. 2003, Wu et al. 2005a). In the case of breast cancer cells, the region that promotes VEGF induction involves the Sp-1 region since mutation in this region abolishes progestin induction of VEGF promoter (Wu et al. 2005a). This signifies that Sp-1 and PR may cooperate in producing this response (as was also found to be the case for estrogen-dependent induction of VEGF in ZR-75 breast cancer cells) (Stoner et al. 2004).

There is evidence that PR isoforms are important factors in VEGF induction in breast cancer cells; PR-B is a more potent inducer of VEGF than PR-A (Wu et al. 2004), suggesting that PR-B-rich tumors are likely to grow larger than tumors containing predominantly PR-A. Support for this hypothesis was provided in a recent study which demonstrated that larger tumors formed when PR-B-containing cells were grown in vivo (Sartorius et al. 2003). Furthermore, it appears that both anti-estrogens and anti-progestins induce VEGFs from breast cancer cells that are rich in PR-B, implying that anti-hormones are recognized differently based on the PR isoforms present (Wu et al. 2004, 2005b). Thus tumors with a high content of PR-B may be best treated by a combination of anti-hormones and anti-angiogenic agents since human tumors are heterogenous and may exhibit various combinations of steroid receptors and receptors for VEGF.

We showed that all synthetic progestins tested induced VEGF in breast cancer cells, via both phosphatidyl inositol 3 (PI3)-kinase and MAP-kinase pathways (Hyder et al. 2001, Liang et al. 2005). Interestingly, VEGF gene regulation occurred in a cell-and ligand-dependent manner (Wu et al. 2005a). Inhibitors of the PI3-kinase pathway suppressed both cellular VEGF expression and protein release. MAP-kinase inhibitors, however, were unable to inhibit gene transcription in certain cells, while still suppressing protein secretion, suggesting that VEGF can be regulated at both transcriptional and post-transcriptional levels by progestins. Intriguingly, progestin-dependent induction of VEGF was blocked by the anti-estrogen ICI 182,780 at both the protein and transcriptional level, suggesting that there may be cross-talk mechanisms involved in such regulation between the two receptors (Hyder & Stancel 2002), a situation analogous to the previously described regulation of the c-src pathway (Ballare et al. 2003).

Using a small series of breast cancer cells, we recently showed that progestin-dependent induction of VEGF occurs only in PR-containing cells that either lack p53 or possess a mutation in the p53 gene (Liang et al. 2005). Progestin-dependent induction did not occur in cells that contained wild-type p53 protein or in cells that were transfected with the wild-type p53 expression plasmid (Liang et al. 2005). Furthermore, we demonstrated that progestin-induced VEGF was angiogenically active, inducing not only endothelial cell proliferation but also proliferation of breast cancer cells via autocrine and paracrine mechanisms as long as the recipient breast cancer cells exhibited VEGFR-2 (Liang & Hyder 2005). These observations lend further support to our hypothesis that increased risk of breast cancer due to progestin exposure may involve progestin-dependent proliferation of pre-neoplastic lesions together with cells possessing a mixture of PR-containing and PR-negative cells, as long as the latter contain VEGF receptors. Further support that progesterone can promote increased growth rates of breast tumors comes from studies in p53 knockout mice that were treated with DMBA (Medina et al. 2003), and we recently showed that progestins increase VEGF expression and accelerate tumors in a rat model of DMBA-induced tumorigenesis in a development stage-dependent manner (Benakanakere et al. 2005). These findings underscore the importance of the p53 tumor suppressor in keeping tumor growth and expansion under the influence of steroid hormones.

While we have information concerning the presence of VEGF receptors in breast cancer cells, our understanding of their regulation by progestins is lacking and requires further research. The picture which is emerging however, is that in breast cancer cells, regulation of the angiogenic pathway, which involves VEGF and VEGF receptors, is under the control of both estrogens and progestins. Currently, very little is known about the molecular mechanisms that regulate such expression, or the biological consequences which arise following induction or suppression of VEGF and VEGF receptors in breast tissue.

	VEGF and anti-hormone resistance

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
As discussed above, both estrogens and progestins induce VEGF in breast cancer cells through their respective receptors and via characterized hormone response elements. Anti-estrogens and anti-progestins cause some hormone-dependent tumors to regress; however, some tumor cells invariably become resistant to anti-hormones and continue to grow (Gutierrez et al. 2005). In certain cases, anti-hormones can even stimulate tumor growth (Clarke et al. 2001). It is not known what specifically causes the resistant cells to continue to proliferate, though it has been suggested that growth factors may be involved (Manders et al. 2003, Nicholson et al. 2005). Interestingly, clinical studies have shown that tumors with high levels of VEGF fail to respond to hormone therapy or have an early recurrence (Foekens et al. 2001, Manders et al. 2003), suggesting that VEGF production may be responsible for anti-hormone resistance. These studies also re-affirm that VEGF may also be responsible for tumor cell proliferation as reported previously (Liang et al. 2005). In this respect, it is interesting to note that many reports indicate that hormone-dependent tumors secrete VEGF in response to either estrogens or progestins (Borgstrom et al. 1999), which might provide a partial explanation for the growth-promoting effects of steroid hormones in breast cancer as well as resistance to anti-hormones. Indeed, our recent data indicate that exposure of breast cancer cells to VEGF can override the effects of anti-hormone (Y Liang, R A Brekken & S M Hyder, unpublished observations), suggesting that a treatment regimen of both anti-hormones and anti-angiogenic agents may be better for tumor suppression than a single regimen alone. In certain cases, anti-hormones have themselves been shown to induce VEGF, suggesting that the nature of the ligand may be altered in a cell- and perhaps receptor isoform-dependent manner (Wu et al. 2004); both anti-progestins and anti-estrogens can induce VEGF in breast cancer cells that express high levels of PR-B (Wu et al. 2005b). For example, anti-estrogens can induce VEGF in MCF-7 cells (Ruhola et al. 1999, Wu et al. 2004, 2005b). Transcriptional and post-transcriptional effects may both be involved in elevating VEGF levels in breast cancer cells. Support for this notion was obtained recently with the identification of hormone response elements in VEGF as well as the analysis of VEGF production from tumor cells with altered levels of receptor isoforms (Wu et al. 2005b).

Potential sex-steroid targets for anti-angiogenic therapy of breast cancer

Angiogenesis is an extremely complex process, which involves many different cell types, all of which must coordinate their growth patterns to establish a well-defined vasculature for nourishment of either normal or tumor tissue. In the latter case, the vasculature can be quite haphazard (Ferrara & Kerbel 2005). Although this review concerns itself chiefly with our understanding of the role played by sex steroids in the control of VEGF in tumor epithelial cells, other cellular and molecular targets which might lead to an overall loss of angiogenic potential of tumor tissue should be considered as potential therapeutic or preventive strategies in breast disease. We need to better understand the role of sex steroids in the stromal compartment of tumor tissue and also in the endothelial cells in breast tumors. While endothelial cells in general do not show any genetic abnormality there are some recent reports that heterogeneity may exist in these cells between normal and tumor tissues (Ribatti et al. 2002). The role of sex steroids may therefore be different in such endothelial cells; there is evidence that endothelial cells do contain estrogen and PRs (Losordo & Isner 2001, Otsuki et al. 2001), although their role in tumor biology is not clear. Similarly, it is not known whether the stroma surrounding the tumor tissue may also be sensitive to anti-hormone. Thus, both endothelial cells and the stromal compartment in and around the tumor may also be targets for anti-hormones in addition to the classically considered epithelial cells.

A number of proteins with anti-angiogenic potential remain to be studied with regard to sex-steroid regulation of breast cancer cell metabolism. These include proteins such as soluble VEGFR-1 (sVEGFR-1), interferon inducible protein 10 (IP-10), endostatin, mammary serine protease inhibitor (maspin), TSP-1 and CD36, the receptor for TSP-1 (reviewed in Dabrosin 2005a). sVEGFR-1 is an alternative spliced form of VEGFR-1 and sequesters VEGF produced from tumor cells, thereby reducing the angiogenic environment. It has been reported that estrogen down regulates the expression of sVEGFR-1 in ER+ breast cancer cells and that this decreased expression is associated with a significant increase in angiogenesis (Elkin et al. 2004). However, a direct role for estrogens or ER in sVEGFR production has not been reported, although such a regulation could be important in designing anti-hormonal therapy of breast disease. Evidence that hormones can have an effect on sVEGFR-1 has come from the observation that during pregnancy, serum levels of sVEGFR-1 are elevated compared with postpartum levels (Koga et al. 2003). The biological significance of this is not known, but it is possible that sVEGFR-1 may be needed to antagonize excessive effects of VEGF on vasculature. Interferon-IP-10 seems to be a strong inhibitor of angiogenesis in vivo and is controlled by interferon (IFN)- (Angiolillo et al. 1995). Estradiol increases IFN- production and an estrogen-responsive element in the IFN- promoter has been found (Fox et al. 1991). In breast cancer, IP-10 was shown to be involved in continued progression of tumor growth and metastasis (Dias et al. 1998, Reome et al. 2004). Since IP-10 is upregulated by IFN-, there is a possibility that sex steroids could influence IP-10 production. It has been reported that exposure of murine mammary epithelial cells to estrogen may decrease the release of local chemokines and disrupt an IP-10-stimulated release of these chemokines from the cells (Aronica et al. 2004). However, in a study of normal breast tissue, in vivo IP-10 did not vary during the menstrual cycle, suggesting that sex steroids have minor effects on IP-10 secretion in the normal breast (Dabrosin 2003). Its role in breast cancer remains to be explored.

Recent studies in tumor biology indicate that TSP-1 and one of its receptors (CD36) possess anti-angiogenic capacities (Armstrong & Bornstein 2003, Simantov & Silverstein 2003). However, the role of TSP-1 is controversial and estrogens seem to induce this factor in breast cancer cells, indicating that it may have additional functions in the breast (S M Hyder, unpublished observation). Consequently, raising TSP-1 levels in breast cancer cells by exogenous means may first appear to be counterintuitive. The role of TSP-1 in proliferation of breast cancer cells has been well studied and it seems that the anti-angiogenic properties of this protein could be context-dependent, perhaps depending on the cleavage product formed as a result of other factors produced from cells, since inhibition of TSP-1 in mouse models prevents the proliferation of tumors (Wang et al. 1996). In addition, it has been shown that CD36, a receptor for TSP-1 that mediates the apoptotic effects of TSP-1 in endothelial cells, is downregulated by estrogens in breast tumor cells (Uray et al. 2004). This may explain why tumor cells proliferate in response to estrogens but do not undergo apoptosis as a result of the TSP-1 they simultaneously secrete, although the exact relationship between TSP-1 and CD36 remains to be explored in breast cancer cells. There are indications that TSP-1 may also be under sex-steroid control in other tissues besides breast cancer cells (Mirkin & Archer 2004). This raises the important question of whether or not it is a good idea to increase endogenous levels of proteins presumed to be anti-angiogenic, in the absence of crucial information as to whether such an action might have harmful as opposed to the desired anti-angiogenic effects.

As with TSP-1, the role of maspin also seems to be context dependent. Maspin was originally identified as a tumor suppressor protein that blocks primary tumor growth as well as invasion and metastasis (Shi et al. 2001). Overexpression of maspin in breast tumor cells has been shown to limit their growth and metastases in vivo and it has been demonstrated that maspin is an effective inhibitor of angiogenesis (Zhang et al. 2000b). It has been suggested that maspin is down-regulated during cancer progression, corresponding to loss of steroid receptors as tumors progress, although one study shows that increased expression of maspin correlates with an aggressive phenotype in breast cancer patients (Umekita et al. 2002). This seemingly contradictory result may be explained by a different biological activity of maspin, which is dependent on its subcellular distribution, since nuclear maspin staining appears to be a good prognostic factor, while cytoplasmic staining is associated with a poor prognostic marker (Mohsin et al. 2003). To date, few studies have investigated the effects of sex steroids on maspin expression, although much remains to be learned in this context. Tamoxifen increases secretion of maspin, whereas maspin secretion was reduced by estradiol in the myoepithelial cells surrounding the breast epithelium (Shao et al. 2000). It has also been demonstrated that tamoxifen induces maspin promoter activity, acting via ER (Khalkhali-Ellis et al. 2004, Liu et al. 2004). However, correlation of maspin and sex-steroid receptor location in breast cancer needs to be further elucidated.

A number of other proteins have been identified which might offer potential targets for triggering anti-angiogenic events in breast cancer, although so far they have received little attention. For example, the angiopoietins (Ang) belong to a family of growth factors, including Ang1, Ang2, Ang3 and Ang4, which can exert both agonist and antagonist action effects on the endothelial receptor tyrosine kinase Tie2 (Metheny-Barlow & Li 2003, Lee et al. 2004) and thereby function as pro-angiogenic or anti-angiogenic factors. For a further discussion on this topic, please refer to Dabrosin (2005a).

Finally, it is becoming increasingly clear that endothelial precursor cells (EPC) play a considerable role in tumor biology. These cells originate in the bone marrow, can be detected in the peripheral circulation and are incorporated into sites of ongoing angiogenesis where they differentiate into mature endothelial cells (Asahara et al. 1997, Lyden et al. 2001). VEGF has a potential role in such recruitment and there is evidence for EPC recruitment in breast cancer cells (Asahara et al. 1999, Shirakawa et al. 2002a,b, Spring et al. 2005). It has been reported that EPCs decline after treatment with anti-angiogenic therapy (Capillo et al. 2003) thus making these cells targets for such therapy (Rafii et al. 2002). However, to date, there is no information available on the role of estrogens or progestins in causing EPCs to mobilize from bone marrow to the target site within the breast. Since EPCs could be targets for preventing tumor expansion and/or angioprevention, it is only a matter of time before studies are reported that address this issue in detail. Considerable effort will be required in this area to understand and establish the role of hormones and anti-hormones in influencing EPC mobilization and whether such mobilization is indeed involved in hormone-dependent incorporation of EPCs in new blood vessels.

	Conclusions

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
Coordinated regulation of angiogenesis and vascular permeability is essential for the physiological functioning of any tissue such as the male and female reproductive tracts. Major health problems such as breast cancer, dysfunctional uterine bleeding, endometriosis, uterine cancer, prostate cancer and male reproductive tract abnormalities almost certainly involve a vascular component. There is a large body of literature that describes the effects of sex steroids on regulation of VEGF in breast cancer cells and on the vasculature of the reproductive tract in general, although the overall picture on sex-steroid regulation of VEGF remains confusing. Moreover, far less is known about the molecular mechanisms that regulate these important actions. There is, therefore, an immense need for mechanistic studies in the area of angiogenesis in order to allow us to better understand the role of sex steroids in the production of angiogenic and naturally existing anti-angiogenic factors. This would likely lead to improved treatment and to a better understanding of how to develop prevention strategies geared to preventing tumors arising in the reproductive tracts of both men and women. The role of angiogenesis in breast cancer is now well recognized and with the recent success of clinically administered angiogenesis inhibitors (Morabito et al. 2004, Moses et al. 2004, Jain 2005, Ryden et al. 2005), the use of such compounds for "angioprevention" of breast cancer would seem to be on the horizon. It should be mentioned that a number of anti-angiogenic approaches are being taken in the field of breast cancer. It is an extremely exciting time to be working in this field of research and to explore how such treatment protocols might influence angiogenic processes and arrest the growth of breast tumors. It will also be important to establish how hormones and anti-hormones influence the angiogenic balance in human tumors and to ascertain whether such alterations are dependent on polymorphisms in various genes related to angiogenesis. It remains to be established whether the area of angiogenesis, as it pertains to breast cancer, is ready for the application of a pharmacogenomic approach by which we might predict how individuals will respond to hormones and anti-hormones. Furthermore, it is imperative that we understand what controls the hormone-controlled angiogenic ‘switch’, since doing so will give us the potential to control or even eradicate breast tumors and gain a much-needed victory over this insidious and deadly disease.

	Acknowledgements

 
I would like to apologize to those investigators whose work could not be cited due to the extent of this review. Our studies on the role of hormones on angiogenic growth factors in breast cancer cells were initially started in collaboration with Dr George Stancel at the University of Texas in Houston, whose contributions, support and advice were invaluable to the author. Thus, it would be appropriate to dedicate this review to his name. I am grateful to talented individuals in the laboratory, both past and present, who have been instrumental in obtaining the exciting data reported elsewhere and discussed herein. These include Drs Yayun Liang, Indira Benakanakere, Jianbo Wu, Sandra Brandt, Ms Jennifer Schnell, Ms Constance Chiappetta and Ms Lata Murthy. I am also grateful to various collaborators for their contribution; in particular to Drs George Stancel, Zafar Nawaz and Cynthia Besch-Williford. I would like to thank Dr Simon Slight for critically reading the manuscript and to Ms Schnell for compiling the references reported in the review.

	Funding

The following sources are acknowledged for the support of studies on angiogenesis: NIH grants CA-86916 and HD-08615, the Susan G Komen Breast Cancer Foundation, American Heart Association, Fleming/Davenport Award from the Texas Medical Center in Houston, Department of Defense breast cancer concept award (W81XWH-05-1-0416), and COR grants from the College of Veterinary Medicine at the University of Missouri, Columbia. SMH is the Zalk Missouri Professor of Tumor Angiogenesis, and is grateful to Ms Thelma Zalk for her generous gift to the College of Veterinary Medicine, University of Missouri. Ms Zalk’s gift was instrumental in allowing us to make key discoveries related to the role of progestins and angiogenic growth factors in breast cancer. The author declares that there is no conflict of interest that would prejudice the impartiality of this scientific work.

	References

Top Abstract Introduction Angiogenesis in breast cancer VEGF and vascular permeability... Sex-steroid regulation of VEGF... VEGF and anti-hormone resistance Conclusions References

 
Ader DN, South-Paul J, Adera T & Deutser PA 2001 Cyclical mastalgia: prevalence and associated health and behavioral factors. Journal of Psychosomatic Obstetrics and Gynaecology 22 71–76.[Medline]

Akiri G, Nahari D, Finkelstein Y, Le SY, Elroy-Stein O & Levi BZ 1998 Regulation of vascular endothelial growth factor (VEGF) expression is mediated by internal initiation of translation and alternative initiation of transcription. Oncogene 17 227–236.[CrossRef][Web of Science][Medline]

Anan K, Morisaki T, Katano M, Ibuko A, Kitsuki H, Uchiyama A, Kuroki S, Tanaka M & Torisu M 1996 Vascular endothelial growth factor and platelet-derived growth factor are potential angiogenic and metastatic factors in human breast cancer. Surgery 119 333–339.[CrossRef][Web of Science][Medline]

Anderson TJ, Ferguson DJ & Raab GM 1982 Cell turnover in the ‘resting’ human breast: influence of parity, contraceptive pill, age and laterality. British Journal of Cancer 46 376–382.[Web of Science][Medline]

Angiolillo AL, Sgadari C, Taub DD, Liao F, Farber JM, Maheshwari S, Kleinman HK, Reaman GH & Tosato G 1995 Human interferon inducible protein 10 is a potent inhibitor of angiogenesis in vivo. Journal of Experimental Medicine 182 155–162.[Abstract/Free Full Text]

Armstrong LC & Bornstein P 2003 Thrombospondins 1 and 2 function as inhibitors of angiogenesis. Matrix Biology 22 63–71.[CrossRef][Web of Science][Medline]

Aronica SM, Fanti P, Kaminskaya K, Gibbs K, Raiber L, Nazareth M, Bucelli R, Mineo M, Grzybek K, Kumin M et al. 2004 Estrogen disrupts chemokine-mediated chemokine release from mammary cells: implications for the interplay between estrogen and IP-10 in the regulation of mammary tumor formation. Breast Cancer Research and Treatment 84 235–245.[CrossRef][Web of Science][Medline]

Asahara T, Murohara T, Sullivan A, Silver M, van der Zee R, Li T, Witzenbicher N, Schnatteman G & Isner JM 1997 Isolation of putative progenitor endothelial cells for angiogenesis. Science 275 964–967.[Abstract/Free Full Text]

Asahara T, Takahashi T, Masuda H, Kalka C, Chen D, Iwaguro H, Inai Y, Silver M & Isner JM 1999 VEGF contributes to post natal neovascularization by mobilizing bone marrow-derived endothelial progenitor cells. EMBO Journal 18 3964–3972.[CrossRef][Web of Science][Medline]

Atqur-Rehman MA & Toi M 2003 Anti-angiogenic therapy in breast cancer. Biomedicine and Pharmacotherapy 57 463–470.

Augustin HG 2005 Angiogenesis in the female reproductive system. EXS 94 35–52.[Medline]

Ballare C, Uhrig M, Bechtold T, Sancho E, Domenico MD, Migliaccio A, Auricchio F & Beaot M 2003 Two domains of the progesterone receptor interact with the estrogen receptor and are required for progesterone activation of the c-src/Erk pathway in mammalian cells. Molecular and Cellular Biology 23 1994–2008.[Abstract/Free Full Text]

Barleon B, Sozzani S, Zhou D, Weich HA, Mantovani A & Marme D 1996 Migration of human monocytes in response to vascular endothelial growth factor (VEGF) is mediated via the VEGT receptor flt-1. Blood 87 3336–3343.[Abstract/Free Full Text]

Benakanakere I, Besch-Williford C, Schnell JD & Hyder SM 2005 Natural and synthetic progestins accelerate tumor development and increase VEGF production in a chemically induced mammary tumor model: a potentially novel target for anti-angiogenic therapeutics. AACR Special Conference in Advances in Breast Cancer, San Diego, CA. Abstract A15.

Bergers G & Benjamin LE 2003 Tumorigenesis and the angiogenic switch. Nature Reviews Cancer 3 401–410.[CrossRef][Web of Science][Medline]

Bermont L, Lamielle-Musard F, Chezy E, Weisz A & Adessi GL 2001 17ß-estradiol inhibits forskolin-induced vascular endothelial growth factor promoter in MCF-7 breast adenocarcinoma cells. Journal of Steroid Biochemistry and Molecular Biology 78 343–349.[CrossRef][Web of Science][Medline]

Blagosklonny MV, An WG, Romanova LY, Trepel J, Fojo T & Neckers L 1998 p53 inhibits hypoxia-inducible factor-stimulated transcription. Journal of Biological Chemistry 273 11995–11998.[Abstract/Free Full Text]

Bogin L & Degani H 2002 Hormonal regulation of VEGF in orthotopic MCF7 human breast cancer. Cancer Research 62 1948–1951.[Abstract/Free Full Text]

Borgstrom P, Gold DP, Hillan KJ & Ferrara N 1999 Importance of VEGF for breast cancer angiogenesis in vivo: implications from intravital microscopy of combination treatments with an anti-VEGF neutralizing monoclonal antibody and doxorubicin. Anticancer Research 19 4203–4214.[Web of Science][Medline]

Bos R, Zhong H, Hanrahan CF, Mommers EC, Semenza GL, Pinedo HM, Abeloff MD, Simons JW, van Diest PJ & van der Wall E 2001 Levels of hypoxia-inducible factor-1 alpha during breast carcinogenesis. Journal of the National Cancer Institute 93 309–314.[Abstract/Free Full Text]

Bos R, van Diest PJ, de Jong JS, van der Groep P, van der Valk P & van der Wall E 2005 Hypoxia-inducible factor-1alpha is associated with angiogenesis, and expression of bFGF, PDGF-BB, and EGFR in invasive breast cancer. Histopathology 46 31–36.[CrossRef][Web of Science][Medline]

Brem SS, Gullino PM & Medina D 1977 Angiogenesis: a marker for neoplastic transformation of mammary papillary hyperplasia. Science 195 880–882.[Abstract/Free Full Text]

Brenner RM & Slayden OD 1994 Cyclic changes in the primate oviduct and endometrium. In The Physiology of Reproduction, vol 1, pp 541–569. Eds E Knobil & JD Neill. New York: Raven Press.

Brown LF, Berse B, Jackman RW, Toguazzi K, Guidi AJ, Dvorak HF, Senger DR, Connolly JL & Schnitt SJ 1995 Expression of vascular permeability factor (vascular endothelial growth factor) and its receptors in breast cancer. Human Pathology 26 86–91.[CrossRef][Web of Science][Medline]

Buteau-Lozano H, Ancelin M, Lardeux B, Milanini J & Perrot-Applanat M 2002 Transcriptional regulation of vascular endothelial growth factor by estradiol and tamoxifen in breast cancer cells: a complex interplay between estrogen receptors alpha and beta. Cancer Research 62 4977–4984.[Abstract/Free Full Text]

Capillo M, Mancuso P, Gobbi A, Monestirolo G, Pruneri G, Del’Agnola C, Martinelli G, Shultz L & Bertolini F 2003 Continuous infusion of endostatin inhibits differentiation, mobilization, and clonogenic potential of endothelial cell progenitors. Clinical Cancer Research 9 377–382.[Abstract/Free Full Text]

Carmeliet P 2005 Angiogenesis in life, disease, and medicine. Nature 438 932–936.[CrossRef][Medline]

Chen WY, Hankinson SE, Schnitt SJ, Rosner BA, Holmes MD & Colditz GA 2004 Association of hormone replacement therapy to estrogen and progesterone receptor status in invasive breast carcinoma. Cancer 101 1490–1500.[CrossRef][Web of Science][Medline]

Chlebowski RT, Hendrix SL, Langer RD, Stefanick ML, Gass M, Lane D, Rodabough RJ, Gilligan MA, Cyr MG, Thomson CA et al. 2003 Influence of estrogen plus progestin on breast cancer and mammography in healthy postmenopausal women: the Women’s Health Initiative Randomized Trial. Journal of the American Medical Association 289 3243–3253.[Abstract/Free Full Text]

Clarke R, Leonessa F, Welch JN & Skaar TC 2001 Cellular and molecular pharmacology of antiestrogen action and resistance. Pharmacological Reviews 53 25–71.[Abstract/Free Full Text]

Colacurci N, Foraro F, DeFranciscis P, Palermo M & del Vecchio W 2001 Effects of different types of hormone replacement therapy on mammographic density. Maturitas 40 159–164.

Connelly OM, Jericevic BM & Lydon JP 2003 Progesterone receptors in mammary gland development and tumorigenesis. Journal of Mammary Gland Biology and Neoplasia 8 205–214.[CrossRef][Web of Science][Medline]

Coradini D, Pellizzaro C, Speranza A & Daidone MG 2004 Hypoxia and estrogen receptor profile influence the responsiveness of human breast cancer cells to estradiol and antiestrogens. Cellular and Molecular Life Sciences 61 76–82.[CrossRef][Web of Science][Medline]

Cronauer MV, Hittmair A, Eder IE, Hobisch A, Culig Z, Ramoner R, Zhang J, Bartsch G, Reissigl A, Radmayr C et al. 1997 Basic fibroblast growth factor levels in cancer cells and in sera of patients suffering from proliferative disorders of the prostate. Prostate 31 223–233.[CrossRef][Web of Science][Medline]

Cullinan-Bove K & Koos RD 1993 Vascular endothelial growth factor/vascular permeability factor expression in the rat uterus: rapid stimulation by estrogen correlates with estrogen-induced increases in uterine capillary permeability and growth. Endocrinology 133 829–837.[Abstract/Free Full Text]

Dabrosin C 2003 Variability of vascular endothelial normal human breast tissue in vivo during the menstrual cycle. Journal of Clinical Endocrinology and Metabolism 88 2695–2698.[Abstract/Free Full Text]

Dabrosin C 2005a Sex steroid regulation of angiogenesis in breast tissue. Angiogenesis 8 127–136.

Dabrosin C 2005b Positive correlation between estradiol and vascular endothelial growth factor but not fibroblast growth factor-2 in normal human breast tissue in vivo. Clinical Cancer Research 11 8036–8041.[Abstract/Free Full Text]

Dabrosin C, Margetts PJ & Gauldie J 2003a Estradiol increases extracellular levels of vascular endothelial growth factor in vivo in murine mammary cancer. International Journal of Cancer 107 535–540.[CrossRef][Web of Science][Medline]

Dabrosin C, Palmer K, Muller WJ & Gauldie J 2003b Estradiol promotes growth and an giogenesis in polyoma middle T transgenic mouse mammary tumor explants. Breast Cancer Research and Treatment 78 1–6.[CrossRef][Web of Science][Medline]

De Fatta RJ, Turbat-Herrera EA, Li BD, Anderson W & De Benedetti A 1999 Elevated expression of eIF4E in confined early breast cancer lesions: possible role of hypoxia. International Journal of Cancer 80 516–522.[CrossRef][Web of Science][Medline]

De Larco JE, Wuertz BR, Rosner KA, Erickson SA, Gamache DE, Manivel JC & Furcht LT 2001 A potential role for interleukin-8 in the metastatic phenotype of breast carcinoma cells. American Journal of Pathology 158 639–646.[Abstract/Free Full Text]

Dias S, Thomas H & Balkwill F 1998 Multiple molecular and cellular changes associated with tumour stasis and regression during IL-12 therapy of a murine breast cancer model. International Journal of Cancer 75 151–157.[CrossRef][Medline]

Dvorak HF, Brown LF, Detmar M & Dvorak AM 1995 Vascular permeability factor/vascular endothelial growth factor, microvascular hyperpermeability, and angiogenesis. American Journal of Pathology 146 1029–1039.[Abstract]

Elkin M, Orgel A & Kleinman HK 2004 An angiogenic switch in breast cancer involves estrogen and soluble vascular endothelial growth factor receptor 1. Journal of the National Cancer Institute 96 875–878.[Abstract/Free Full Text]

Engels K, Fox SB, Whitehouse RM, Gatter KC & Harris AL 1997a Distinct angiogenic patterns are associated with high-grade in situ ductal carcinomas of the breast. Journal of Pathology 181 207–212.[CrossRef][Medline]

Engels K, Fox SB, Whitehouse RM, Gatter KC & Harris AL 1997b Up-regulation of thymidine phophorylase expression is associated with a discrete pattern of angiogenesis in ductal carcinomas in situ of the breast. Journal of Pathology 182 414–420.[CrossRef][Web of Science][Medline]

Erel CT, Esen G, Seyisoglu H, Elter K, Uras C, Ertungealp E & Aksu MF 2001 Mammographic density increase in women receiving different hormone replacement regimens. Maturitas 40 151–157.

Eriksson U & Alitalo K 1999 Structure, expression, and receptor-binding properties of novel vascular endothelial growth factors. Current Topics in Microbiology and Immunology 237 41–57.[Web of Science][Medline]

Eskens FALM 2004 Angiogenesis inhibitors in clinical development; where are we now and where are we going? British Journal of Cancer 90 1–7.[CrossRef][Web of Science][Medline]

Ferrara N 1999 Vascular endothelial growth factor: molecular and biological aspects. Current Topics in Microbiology and Immunology 237 1–30.[Web of Science][Medline]

Ferrara N 2004a Vascular endothelial growth factor as a target for anticancer therapy. Oncologist 9 2–10.[Abstract/Free Full Text]

Ferrara N 2004b Vascular endothelial growth factor: basic science and clinical progress. Endocrine Reviews 25 581–611.[Abstract/Free Full Text]

Ferrara N 2005 The role of VEGF in the regulation of physiological and pathological angiogenesis. EXS 94 209–231.[Medline]

Ferrara N & Davis-Smyth T 1997 The biology of vascular endothelial growth factor. Endocrinology Reviews 18 4–25.[Abstract/Free Full Text]

Ferrara N & Kerbel RS 2005 Angiogenesis as a therapeutic target. Nature 438 967–974.[CrossRef][Medline]

Ferrara N, Gerber HP & LeCouter J 2003 The biology of VEGF and its receptors. Nature Medicine 9 669–676.[CrossRef][Web of Science][Medline]

Ferrara N, Hillan KJ & Novotny W 2005 Bevacizumab (Avastin), a humanized anti-VEGF monoclonal antibody for cancer therapy. Biochemical and Biophysical Research Communications 333 289–291.[CrossRef][Web of Science][Medline]

Findlay JK 1986 Angiogenesis in reproductive tissues. Journal of Endocrinology 111 357–366.[Abstract/Free Full Text]

Foekens JA, Peters HA, Grebenchtchikov N, Look MP, Meijer-van Gelder ME, Geurts-Moespot A, van der Kwast TH, Sweep CG & Klijn JG 2001 High tumor levels of vascular endothelial growth factor predict poor response to systemic therapy in advanced breast cancer. Cancer Research 61 5407–5414.[Abstract/Free Full Text]

Folkman J 1995 Angiogenesis in cancer, vascular, rheumatoid and other disease. Nature Medicine 1 27–31.[CrossRef][Web of Science][Medline]

Folkman J 1998 Is tissue mass regulated by vascular endothelial cells? Prostate as the first evidence. Endocrinology 139 441–442.[Free Full Text]

Folkman J 2003 Fundamental concepts of the angiogenic process. Current Molecular Medicine 3 643–651.[CrossRef][Web of Science][Medline]

Folkman J & Hanahan D 1991 Switch to the angiogenic phenotype during tumorigenesis. Princess Takamatsu Symposium 22 339–347.

Fox HS, Bond BL & Parslow TG 1991 Estrogen regulates the IFN gamma promoter. Journal of Immunology 146 4362–4367.[Abstract]

Garvin S & Dabrosin C 2003 Tamoxifen inhibits secretion of vascular endothelial growth factor in breast cancer in vivo. Cancer Research 63 8742–8748.[Abstract/Free Full Text]

Garvin S, Nilsson UW & Dabrosin C 2005 Effects of oestradiol and tamoxifen on VEGF, soluble VEGFR-1, and VEGFR-2 in breast cancer and endothelial cells. British Journal of Cancer 93 1005–1010.[CrossRef][Web of Science][Medline]

Gasparini G 1997 Angiogenesis in endocrine-related cancer. Endocrine-Related Cancer 4 423–445.[Abstract/Free Full Text]

Gasparini G 2000 Prognostic value of vascular endothelial growth factor in breast cancer. Oncologist 5 S37–S44.

Gasparini G, Toi M, Miceli R, Vermuelen PB, Dittadi R, Biganzoli E, Morabito A, Fanell M, Gatti C, Suzuki H et al. 1999 Clinical relevance of vascular endothelial growth factor and thymidine phosphorylase in patients with node-positive breast cancer treated with either adjuvant chemotherapy or hormone therapy. Cancer Journal from Scientific American 5 101–111.[Medline]

Gasparini G, Longo R, Torino F & Morabito A 2005 Therapy of breast cancer with molecular targeting agents. Annals of Oncology 16 (Suppl 4) iv28–iv36.[Abstract/Free Full Text]

Gimbrone MA Jr & Gullion PM 1976 Angiogenic capacity of preneoplastic lesions of the murine mammary gland as a marker of neoplastic transformation. Cancer Research 36 2611–2620.[Abstract/Free Full Text]

Goldberg ID & Rosen EM 1997 Regulation of angiogenesis. EXS 79.

Greb RR, Heikinheimo O, Williams RF, Hodgen GD & Goodman AL 1997 Vascular endothelial growth factor in primate endometrium is regulated by oestrogen-receptor and progesterone-receptor ligands in vivo. Human Reproduction 12 1280–1292.[Abstract/Free Full Text]

Guidi AJ, Fischer L, Harris JR & Schnitt SJ 1994 Microvessel density and distribution in ductal carcinoma in situ of the breast. Journal of the National Cancer Institute 86 614–619.[Abstract/Free Full Text]

Guidi AJ, Schnitt SJ, Fischer L, Tognazzi K, Harris JR, Dvorak HF & Brown LF 1997 Vascular permeability factor (vascular endothelial growth factor) expression and angiogenesis in patients with ductal carcinoma in situ of the breast. Cancer 15 1945–1953.

Guinebretiere JM, LeMonique G, Gavoille A, Bahi J & Contesso G 1994 Angiogenesis and risk of breast cancer in women with fibrocystic disease. Journal of the National Cancer Institute 86 635–636.[Free Full Text]

Gutierrez MC, Detre S, Johnston S, Mohsin SK, Shou J, Allred DC, Schiff R, Osborne CK & Dowsett M 2005 Molecular changes in tamoxifen-resistant breast cancer: relationship between estrogen receptor, HER-2, and p38 mitogen-activated protein kinase. Journal of Clinical Oncology 23 2469–2476.[Abstract/Free Full Text]

Hicklin DJ & Ellis LM 2005 Role of the vascular endothelial growth factor pathway in tumor growth and angiogenesis. Journal of Clinical Oncology 23 1011–1027.[Abstract/Free Full Text]

Hoeben A, Landuyt B, Highley MS, Wildiers H, Van Oosterom AT & De Bruijn EA 2004 Vascular endothelial growth factor and angiogenesis. Pharmacological Review 56 549–580.[Abstract/Free Full Text]

Huh JI, Calvo A, Stafford J, Cheung M, Kumar R, Philp D, Kleinman HK & Green JE 2004 Inhibition of VEGF receptors significantly impairs mammary cancer growth in C3(1)/Tag transgenic mice through antiangiogenic and non-antiangiogenic mechanisms. Oncogene 24 790–800.

Hyder SM 2002 The role of steroid hormones on the regulation of vascular endothelial growth factor. American Journal Pathology 161 345–346.

Hyder SM & Stancel GM 1999 Regulation of angiogenic growth factors in the female reproductive tract by estrogens and progestins. Molecular Endocrinology 13 806–811.[Free Full Text]

Hyder SM & Stancel GM 2000 Regulation of VEGF in the reproductive tract by sex-steroid hormones. Histology and Histopathology 15 325–334.[Web of Science][Medline]

Hyder SM & Stancel GM 2002 Inhibition of progesterone-induced VEGF production in human breast cancer cells by the pure antiestrogen ICI 182,780. Cancer Letters 181 47–53.[CrossRef][Web of Science][Medline]

Hyder SM, Nawaz Z, Chiappetta C, Yokoyama K & Stancel GM 1995 The protooncogene c-jun contains an unusual estrogen-inducible enhancer within the coding sequence. Journal of Biological Chemistry 270 8506–8513.[Abstract/Free Full Text]

Hyder SM, Stancel GM, Chiappetta C, Murthy L, Boettger-Tong HL & Makela S 1996 Uterine expression of vascular endothelial growth factor is increased by estradiol and tamoxifen. Cancer Research 56 3954–3960.[Abstract/Free Full Text]

Hyder SM, Chiappetta C, Murthy L & Stancel GM 1997 Selective inhibition of estrogen-regulated gene expression in vivo by the pure antiestrogen ICI 182,780. Cancer Research 57 2547–2549.[Abstract/Free Full Text]

Hyder SM, Murthy L & Stancel GM 1998 Progestin regulation of vascular endothelial growth factor in human breast cancer cells. Cancer Research 58 392–395.[Abstract/Free Full Text]

Hyder SM, Nawaz Z, Chiappetta C & Stancel GM 2000a Identification of functional estrogen response elements in the gene coding for the potent angiogenic factor vascular endothelial growth factor. Cancer Research 60 3183–3190.[Abstract/Free Full Text]

Hyder SM, Huang JC, Nawaz Z, Boettger-Tong H, Makela S, Chiappetta C & Stancel GM 2000b Regulation of vascular endothelial growth factor expressions by estrogens and progestins. Environmental Health Perspectives 108 785–790.[Web of Science][Medline]

Hyder SM, Chiappetta C & Stancel GM 2001 Pharmacological and endogenous progestins induce vascular endothelial growth factor expression in human breast cancer cells. International Journal of Cancer 92 469–473.[CrossRef][Web of Science][Medline]

Jain R 2005 Normalization of tumor vasculature: an emerging concept in anti-angiogenic therapy. Science 307 58–62.[Abstract/Free Full Text]

Jain RK, Duda DG, Clark JW & Loeffler JS 2006 Lessons from phase III clinical trials on anti-VEGF therapy for cancer. Nature Clinical Practice & Oncology 3 24–40.[Medline]

Jeltsch M, Kaipainen A, Joukov V, Meng X, Lakso M, Rauvala H, Swartz M, Fukumura D, Jain RK, Alitalo K 1997. Hyperplasia of lymphatic vessels in VEGF-C transgenic mice. Science 276 1423–1425. Erratum in: Science 277 463.[Abstract/Free Full Text]

Jensen HM, Chen I, DeVault MF & Lewis AE 1982 Angiogenesis induced by "normal" human breast tissue: a probable marker for precancer. Science 218 293–295.[Abstract/Free Full Text]

de Jong JS, van Diest PJ, van der Valk P & Baak JP 1998 Expression of growth factors, growth inhibiting factors, and their receptors in invasive breast cancer. I: An inventory in search of autocrine and paracrine loops. Journal of Pathology 184 44–52.[CrossRef][Web of Science][Medline]

Kaklamani VG & Gradishar WJ 2005 Adjuvant therapy of breast cancer. Cancer Investigation 23 548–560.[CrossRef][Web of Science][Medline]

Kazi AA, Jones JM & Koos RD 2005 Chromatin immunoprecipitation analysis of gene expression in the rat uterus in vivo: estrogen-induced recruitment of both estrogen receptor alpha and hypoxia inducible factor 1 to the vascular endothelial growth factor promoter. Molecular Endocrinology 19 2006–2019.[Abstract/Free Full Text]

Kevil CG, De Benedetti A, Payne DK, Coe LL, Laroux FS & Alexander JS 1996 Translational regulation of vascular permeability factor by eukaryotic initiation factor 4E: implications for tumor angiogenesis. International Journal of Cancer 65 785–790.[CrossRef][Web of Science][Medline]

Khalkhali-Ellis Z, Christian AL, Kirschmann DA, Edwards EM, Rezaie-Thompson M, Vasef MA, Gruman LM, Seftor RE, Norwood LE & Hendrix MJ 2004 Regulating the tumor suppressor gene maspin in breast cancer cells: a potential mechanism for the anticancer properties of tamoxifen. Clinical Cancer Research 10 449–454.[Abstract/Free Full Text]

Koga K, Osuga Y, Yoshino O, Hirota Y, Fuimeng X, Hirata T, Takea S, Yano T, Tsutmi O & Taketami Y 2003 Elevated serum soluble vascular endothelial growth factor receptor 1 (sVEGFR-1) levels in women with preeclampsia. Journal of Clinical Endocrinology and Metabolism 88 2348–2351.[Abstract]

Krippl P, Langsenlehner U, Renner W, Yazdani-Biuki B, Wolf G, Wascer TG, Paulweber B, Haas J & Samonigg H 2003 A common 936 C/T gene polymorphism of vascular endothelial growth factor is associated with decreased breast cancer risk. International Journal of Cancer 106 468–471.[CrossRef][Web of Science][Medline]

Krippl P, Langsenlehner U, Samonigg H, Renner W & Koppel H 2004 Vascular endothelial growth factor in predicting outcome in breast cancer. Clinical Cancer Research 10 8752–8753.[Free Full Text]

Kucab JE & Dunn SE 2003 Role of IGF-1R in mediating breast cancer invasion and metastasis. Breast Disease 17 41–47.[Medline]

Kurebayashi J, Otsuki T, Moriya T & Sonoo H 2001 Hypoxia reduces hormone responsiveness of human breast cancer cells. Japanese Journal of Cancer Research 92 1093–1101.[CrossRef][Web of Science]

Lanari C & Molinolo A 2002 Progesterone receptors–animal models and cell signaling in breast cancer, diverse activation pathways for the progesterone receptor: possible implications for breast biology and cancer. Breast Cancer Research 4 240–243.[CrossRef][Web of Science][Medline]

Lee AH, Dublin EA, Bobrow LG & Poulsom R 1998 Invasive lobular and invasive ductal carcinoma of the breast show distinct patterns of vascular endothelial growth factor expression and angiogenesis. Journal of Pathology 185 394–401.[CrossRef][Web of Science][Medline]

Lee HJ, Cho CH, Hwang SJ, Choi HH, Kim KT, Ahn Sy, On JL, Lee GM & Koh GY 2004 Biological characterization of angiopoietin-3 and angiopoietin-4. FASEB Journal 18 1200–1208.[Abstract/Free Full Text]

Liang Y & Hyder SM 2005 Proliferation of endothelial and tumor epithelial cells by progestin-induced vascular endothelial growth factor from human breast cancer cells: paracrine and autocrine effects. Endocrinology 146 3632–3641.[Abstract/Free Full Text]

Liang Y, Wu J & Hyder SM 2005 p53-dependent inhibition of progestin-induced VEGF expression in human breast cancer cells. Journal of Steroid Biochemistry and Molecular Biology 93 173–182.[CrossRef][Web of Science][Medline]

Lichtenbeld HC, Barendsz-Janson AF, ven Essen H, Struijker Boudeier H, Griffioen AW & Hillen HF 1998 Angiogenic potential of malignant and non-malignant human breast tissues in an in vivo angiogenesis model. International Journal of Cancer 77 455–459.[CrossRef][Medline]

Lin Y, Huang R, Chen L, Li S, Shi Q, Jordan C & Huang RP 2004 Identification of interleukin-8 as estrogen receptor-regulated factor involved in breast cancer invasion and angiogenesis by protein arrays. International Journal of Cancer 109 507–515.[CrossRef][Web of Science][Medline]

Linderholm B, Travelin B, Grankvist K & Henriksson R 1998 Vascular endothelial growth factor is of high prognostic value in node-negative breast carcinoma. Journal of Clinical Oncology 16 3121–3128.[Abstract/Free Full Text]

Linderholm B, Lindh B, Tavelin B, Grankvist K & Henriksson R 2000a p53 and vascular-endothelial-growth-factor (VEGF) expression predicts outcome in 833 patients with primary breast carcinoma. International Journal of Cancer 89 51–62.[CrossRef][Web of Science][Medline]

Linderholm B, Grankvist K, Wilking N, Johansson M, Tavelin B & Henriksson R 2000b Correlation of vascular endothelial growth factor content with recurrences, survival, and first relapse site in primary node-positive breast carcinoma after adjuvant therapy. Journal of Clinical Oncology 18 1423–1431.[Abstract/Free Full Text]

Linderholm BK, Lindhal T, Holmberg L, Klaar S, Lennerstrand J, Henriksson R & Bergh J 2001 The expression of vascular endothelial growth factor correlates with mutant p53 and poor prognosis in human breast cancer. Cancer Research 61 2256–2260.[Abstract/Free Full Text]

Liu Z, Shi HY, Nawaz Z & Zhang M 2004 Tamoxifen induces the expression of maspin through estrogen receptor-alpha. Cancer Letters 209 55–65.[CrossRef][Web of Science][Medline]

Longo R, Sarmiento R, Fanelli M, Capaccetti B, Gattuso D & Gasparini G 2002 Anti-angiogenic therapy: rationale, challenges and clinical studies. Angiogenesis 5 237–256.[CrossRef][Medline]

Losordo DW & Isner JM 2001 Estrogen and angiogenesis: a review. Arteriosclerosis Thrombosis and Vascular Biology 21 6–12.[Abstract/Free Full Text]

Lyden D, Hattori K & Dias S 2001 Impaired recruitment of bone marrow-derived endothelial and hematopoietic precursor cells blocks tumor angiogenesis and growth. Nature Medicine 7 1194–1201.[CrossRef][Web of Science][Medline]

McLeskey SW, Tobias CA, Vezza PR, Filie AC, Kern FG & Hanfelt J 1998 Tumor growth of FGF or VEGF transfected MCF-7 breast carcinoma cells correlates with density of specific microvessels independent of the transfected angiogenic factor. American Journal of Pathology 153 1993–2006.[Abstract/Free Full Text]

Maiorana A & Gullino PM 1978 Acquisition of angiogenic capacity and neoplastic transformation in the rat mammary gland. Cancer Research 38 4409–4414.[Abstract/Free Full Text]

Mamane Y, Petroulakis E, Rong L, Yoshida K, Ler LW & Sonenberg N 2004 eIF4E–from translation to transformation. Oncogene 23 3172–3179.[CrossRef][Web of Science][Medline]

Manders P, Beex LV, Tjan-Heijnen VC, Span PN & Sweep CG 2003 Vascular endothelial growth factor is associated with the efficacy of endocrine therapy in patients with advanced breast carcinoma. Cancer 98 2125–2132.

Martin L, Finn CA & Trinder G 1973 Hypertrophy and hyperplasia in the mouse uterus after oestrogen treatment: an autoradiographic study. Journal of Endocrinology 56 133–144.[Abstract/Free Full Text]

Medina D, Kittrell FS, Shepard A, Contreras A, Rosen JM & Lydon J 2003 Hormone dependence in premalignant mammary progression. Cancer Research 63 1067–1072.[Abstract/Free Full Text]

Metheny-Barlow LJ & Li LY 2003 The enigmatic role of angiopoietin-1 in tumor angiogenesis. Cell Research 13 309–317.[CrossRef][Web of Science][Medline]

Meunier-Carpentier S, Dales JP, Djemli A, Garcia S, Bonnier P, Andrac-Meyer L, Lavaut MN, Allasia C & Charpin C 2005 Comparison of the prognosis indication of VEGFR-1 and VEGFR-2 and Tie2 receptor expression in breast carcinoma. International Journal of Oncology 26 977–984.[Web of Science][Medline]

Meyer M, Clauss M, Lepple-Wienhues A, Waltenberger J, Augustin HG, Ziche M, Lanz C, Bitner M, Rziha HJ, Dehio C 1999 A novel vascular endothelial growth factor encoded by Orf virus, VEGF-E, mediates angiogenesis via signaling through VEGFR-2 (KDR) but not VEGFR-1 (Flt-1) receptor tyrosine kinases. EMBO Journal 18 363–374.[CrossRef][Web of Science][Medline]

Milanini-Mongiat J, Pouyssegur J & Pages G 2002 Identification of two Sp1 phosphorylation sites for p42/p44 mitogen-activated protein kinases: their implication in vascular endothelial growth factor gene transcription. Journal of Biological Chemistry 277 20631–20639.[Abstract/Free Full Text]

Mirkin S & Archer DF 2004 Effects of mifepristone on vascular endothelial growth factor and thrombospondi-1 mRNA in Ishikawa cells: implications for endometrial effects of mifepristone. Contraception 70 327–333.

Mirkin S, Wong BC & Archer DF 2005 Effect of 17ß-estradiol, progesterone, synthetic progestins, tibolone, and tibolone metabolites on vascular endothelial growth factor mRNA in breast cancer cells. Fertility and Sterility 84 485–491.[CrossRef][Web of Science][Medline]

Mohsin SK, Zhang M, Clark GM & Craig Allred D 2003 Maspin expression in invasive breast cancer: association with other prognostic factors. Journal of Pathology 199 432–435.[CrossRef][Web of Science][Medline]

Moore MR 2004 A rationale for inhibiting progesterone-related pathways to combat breast cancer. Current Cancer Drug Targets 4 183–189.[CrossRef][Web of Science][Medline]

Morabito A, Sarmiento R, Bonginelli P & Gasparini G 2004 Antiangiogenic strategies, compounds and early clinical results in breast cancer. Critical Reviews in Oncology/Hematology 49 91–107.[Web of Science][Medline]

Moses MA, Harper J & Fernandez CA 2004 A role for antiangiogenic therapy in breast cancer. Current Oncology Report 6 42–48.

Mueller MD, Vigne JL, Minchenko A, Lebovie Di, Leitman DC & Taylor RN 2000 Regulation of vascular endothelial growth factor (VEGF) gene transcription by estrogen receptors alpha and beta. PNAS 97 10972–10977.[Abstract/Free Full Text]

Mueller MD, Vigne JL, Pritts EA, Chao V, Dreher E & Taylor RN 2003 Progestins activate vascular endothelial growth factor gene transcription in endometrial adenocarcinoma cells. Fertility and Sterility 79 386–392.[CrossRef][Web of Science][Medline]

Nakamura J, Savinvov A, Lu Q & Brodie A 1996 Estrogen regulates vascular endothelial growth/permeability factor expression in 7,12-dimethylbenz(a) anthracene-induced rat mammary tumors. Endocrinology 137 5589–5596.[Abstract]

Nakamura J, Lu Q, Aberdeen G, Albrecht E & Brodie A 1999 The effect of estrogen on aromatase and vascular endothelial growth factor messenger ribonucleic acid in the normal nonhuman primate mammary gland. Journal of Clinical Endocrinology and Metabolism 84 1432–1437.[Abstract/Free Full Text]

Nakopoulou L, Stefanaki K, Panayotopoulou E, Giannopoulou I, Athanassiadou P, Gakiopoulou-Givalou H & Louvrou A 2002 Expression of the vascular endothelial growth factor receptor-2/Flk-1 in breast carcinomas: correlation with proliferation. Human Pathology 33 863–870.[CrossRef][Web of Science][Medline]

Nathan CA, Carter P, Liu L, Li BD, Abreo F, Tudor A, Zimmer SG & De Benedetti A 1997 Elevated expression of eIF4E and FGF-2 isoforms during vascularization of breast carcinomas. Oncogene 15 1087–1094.[CrossRef][Web of Science][Medline]

Naumov GN, Bender E, Zurakowski D, Kang SY, Sampson D, Flynn E, Watnick RS, Straume O, Akslen LA, Folkman J et al. 2006 A model of human tumor dormancy: an angiogenic switch from the nonangiogenic phenotype.. Journal of the National Cancer Institue 98 316–325.

Navolanic PM & McCubrey JA 2005 Pharmacological breast cancer therapy (review). International Journal of Oncology 27 1341–1344.[Web of Science][Medline]

Neufeld G, Cohen T, Gengrinovitch S & Poltorak Z 1999 Vascular endothelial growth factor (VEGF) and its receptors. FASEB Journal 13 9–22.[Abstract/Free Full Text]

Nicholson RI, Hutcheson IR, Hiscox SE, Knowlden JM, Giles M, Barrow D & Gee JMW 2005 Growth factor signaling and resistance to selective oestrogen receptor modulators and pure anti-oestrogens: the use of anti-growth factor therapies to treat or delay endocrine resistance in breast cancer. Endocrine-Related Cancer 12 S29–S36.[Abstract/Free Full Text]

Nicosia RR & Villaschi S 1999 Autoregulation of angio-genesis by cells of the vessel wall. International Reviews of Cytology 185 1–43.

Noh JJ, Maskarinec G, Pagano I, Cheung LW & Stanchyk FZ 2005 Mammographic densities and circulating hormones: a cross-sectional study in premenopausal women. Breast In Press.

Ortega N, Hutchings H & Plouet J 1999 Signal relays in the VEGF system. Frontiers of Bioscience 4 141–152.

Otsuki M, Saito H, Xu X, Sumitani S, Souhara H, Kishimoto T & Kasayama S 2001 Progesterone, but not medroxyprogesterone, inhibits vascular cell adhesion vascular cell adhesion molecule-1 expression in human vascular endothelial cells. Arteriosclerosis Thrombosis and Vascular Biology 21 243–248.[Abstract/Free Full Text]

Pages G & Pouyssegur J 2005 Transcriptional regulation of the vascular endothelial growth factor gene—a concert of activating factors. Cardiovascular Research 65 564–573.[Abstract/Free Full Text]

Pal S, Claffey KP, Cohen HT & Mukhopadhyay D 1998 Activation of Sp1-mediated vascular permeability factor/vascular endothelial growth factor transcription requires specific interaction with protein kinase C zeta. Journal of Biological Chemistry 273 26277–26280.[Abstract/Free Full Text]

Pal S, Datta K & Mukhopadhyay D 2001 Central role of p53 on regulation of vascular permeability factor/ vascular endothelial growth factor (VPF/VEGF) expression in mammary carcinoma. Cancer Research 61 6952–6957.[Abstract/Free Full Text]

Pasqualini JR 2000 In Breast Cancer: Prognosis, Treatment and Prevention. New York: Marcel Dekker.

Pekala P, Marlow M, Heuvelman D & Connolly D 1990 Regulation of hexose transport in aortic endothelial cells by vascular permeability factor and tumor necrosis factor-alpha, but not by insulin. Journal of Biological Chemistry 265 18051–18054.[Abstract/Free Full Text]

Price DJ, Miralem T, Jiang S, Steinberg R & Avraham H 2001 Role of vascular endothelial growth factor in the stimulation of cellular invasion and signaling of breast cancer cells. Cell Growth and Differentiation 12 129–135.[Abstract/Free Full Text]

Rafii S, Lyden D, Benezra R, Hattori K & Heissig B 2002 Vascular and hematopoietic stem cells: novel targets for anti-angiogenesis therapy? Nature Reviews Cancer 2 826–835.[CrossRef][Web of Science][Medline]

Ragaz J, Miller K, Badve S, Dayachko Y, Dunn S, Nielsen T, Brodie A, Huntsman D, Bajdik C et al. 2004 Adverse association of expressed vascular endothelial growth factor (VEGF) Her2, Cox2, uPA, and EMSY with long-term outcome of stage I—III breast cancer (BrCA). Results from the British Columbia Tissue Microarray Project. Proceedings of the American Society of Clinical Oncology 23 8.

Rak J, Filmus J, Finkenzeller G, Grugel S, Marme D & Kerbel RS 1995 Oncogenes as inducers of tumor angiogenesis. Cancer Metastasis Review 14 263–277.

Rak J, Filmus J & Kerbel RS 1996 Reciprocal paracrine interactions between tumor cells and endothelial cells: the ‘angiogenesis progression’ hypothesis. European Journal of Cancer 32 2438–2450.

Relf M, LeJeune S, Scott PA, Fox S, Smith K, Lee R, Moghaddam A, Whitehouse R, Bicknell R & Harris AL 1997 Expression of the angiogenic factors vascular endothelial cell growth factor, acidic and basic fibroblast growth factor, tumor growth factor beta-1, platelet-derived endothelial cell growth factor, placental growth factor, and pleiotrophin in human primary breast cancer and its relation to angiogenesis. Cancer Research 57 963–969.[Abstract/Free Full Text]

Reome JB, Hylind JC, Dutton RW & Dobrazanski MJ 2004 Type 1 and type 2 tumor infiltrating effector cell subpopulations in progressive breast cancer. Clinical Immunology 111 69–81.[CrossRef][Medline]

Reynolds LP, Killilea SD & Redmer DA 1992 Angiogenesis in the female reproductive system. FASEB Journal 6 886–892.[Abstract]

Ribatti D, Nico B, Vacca A, Roncali L & Dammacco F 2002 Endothelial cell heterogeneity and organ specificity. Journal of Hematotherapy and Stem Cell Research 11 81–90.

Risau W 1997 Mechanisms of angiogenesis. Nature 386 671–674.[CrossRef][Medline]

Roberts WG & Palade GE 1995 Increased microvascular permeability and endothelial fenestration induced by vascular endothelial growth factor. Journal of Cellular Sciences 108 2369–2379.

Ross RK, Paganini-Hill A, Wan PC & Pike MC 2000 Effect of hormone replacement therapy on breast cancer risk: estrogen versus estrogen plus progestin. Journal of the National Cancer Institute 92 328–332.[Abstract/Free Full Text]

Ruhola JK, Valve EM, Karkkainen MJ, Joukov V, Alitalo K & Harkonene PL 1999 Vascular endothelial growth factors are differentially regulated by steroid hormones and antiestrogens in breast cancer cells. Molecular and Cellular Endocrinology 149 29–40.[CrossRef][Web of Science][Medline]

Ryden L, Linderholm B, Nielsen NH, Erndin S, Jonsson PE & Landberg G 2003 Tumor specific VEGF-A and VEGF2/KDR protein are co-expressed in breast cancer. Breast Cancer Research and Treatment 82 147–154.[CrossRef][Web of Science][Medline]

Ryden L, Jirstrom K, Bendahl PO, Ferno M, Nordenskjold B, Stal O, Thorstenson S, Jonsson PE & Landberg G 2005 Tumor specific expression of vascular endothelial growth factor receptor 2 but not vascular endothelial growth factor or human epidermal growth factor receptor 2 is associated with impaired response to adjuvant tamoxifen in premeopausal women. Journal of Clinical Oncology 23 4695–4704.[Abstract/Free Full Text]

Saaristo A, Karpanen T & Alitalo K 2000 Mechanisms of angiogenesis and their use in the inhibition of tumor growth and metastasis. Oncogene 19 6122–6129.[CrossRef][Web of Science][Medline]

Sartorius CA, Shen T & Horwitz KB 2003 Progesterone receptors A and B differentially affect the growth of estrogen-dependent human breast tumor xenografts. Breast Cancer Research and Treatment 79 287–299.[CrossRef][Web of Science][Medline]

Schairer C 2002 Progesterone receptors—animal models and cell signaling in breast cancer, implications for breast cancer of inclusion of progestins in hormone replacement therapies. Breast Cancer Research 4 244–248.[CrossRef][Medline]

Schneider BP & Miller KD 2005 Angiogenesis of breast cancer. Journal of Clinical Oncology 23 1782–1790.[Free Full Text]

Schoeffner DJ, Matheny SL, Akahane T, Factor V, Berry A, Merlino G & Thorgeirsson UP 2005 VEGF contributes to mammary tumor growth in transgenic mice through paracrine and autocrine mechanisms. Laboratory Investigation 85 608–623.[CrossRef][Web of Science][Medline]

Sengupta K, Banerjee S, Saxena H & Banerjee SK 2003 Estradiol-induced vascular endothelial growth factor-A expression in breast tumor cells is biphasic and regulated by estrogen receptor-alpha dependent pathway. International Journal of Oncology 22 609–614.[Web of Science][Medline]

Shao ZM, Radziszewski WJ & Barsky SH 2000 Tamoxifen enhances myoepithelial cell suppression of human breast carcinoma progression in vitro by two different effector mechanisms. Cancer Letters 157 133–144.[CrossRef][Web of Science][Medline]

Shi HY, Zhang W, Liang R, Abraham S, Kittrell FS, Medina D & Zhang M 2001 Blocking tumor growth, invasion, and metastasis by maspin in a syngeneic breast cancer model. Cancer Research 61 6945–6951.[Abstract/Free Full Text]

Shirakawa K, Furuhata S, Watanabe I, Hayase H, Shimizu A, Ikarashi Y, Yoshida T, Terada M, Hashimoto D et al. 2002a Induction of vasculogenesis in breast cancer models. British Journal of Cancer 87 1454–1461.[CrossRef][Web of Science][Medline]

Shirakawa K, Shibuya M, Heike Y, Takashima S, Watanabe I, Konishi F, Kasumi F, Goldman CK, Thomas KA, Bett A 2002b Tumor-infiltrating endothelial cells and endothelial precursor cells in inflammatory breast cancer. International Journal of Cancer 99 344–351.[CrossRef][Web of Science][Medline]

Simantov R & Silverstein RL 2003 CD36: a critical anti-angiogenic receptor. Frontiers in Bioscience 8 S874–S882.[CrossRef][Medline]

Sledge GW Jr & Miller KD 2003 Exploiting the hallmarks of cancer: the future conquest of breast cancer. European Journal of Cancer 39 1668–1675.[Medline]

Soderqvist G, Isaksson E, von Schoultz B, Carlstrom K, Tani E & Skoog L 1997 Proliferation of breast epithelial cells in healthy women during the menstrual cycle. American Journal of Obstetrics and Gynecology 176 123–128.[CrossRef][Web of Science][Medline]

Sordello S, Bertrand N & Plouet J 1998 Vascular endothelial growth factor is up-regulated in vitro and in vivo by androgens. Biochemical and Biophysical Research Communications 251 287–290.[CrossRef][Web of Science][Medline]

Soufla G, Porchis R, Sourvinos G, Vassilaros S & Spandidos DA 2005 Transcriptional deregulation of VEGF, FGF2, TGF-beta1, 2, 3, and cognate receptors in breast tumorigenesis. Cancer Letters In Press.

Speirs V & Atkin SL 1999 Production of VEGF and expression of the VEGF receptors Flt-1 and KDR in primary cultures of epithelial and stromal cells derived from breast tumors. British Journal of Cancer 80 898–903.[CrossRef][Web of Science][Medline]

Spring H, Schuler T, Arnold B, Hammerling GJ & Ganss R 2005 Chemokines direct endothelial progenitors into tumor neovessels. PNAS 102 18111–18116.[Abstract/Free Full Text]

Stevens A, Soden J, Brenchley PE, Ralph S & Ray DW 2003 Haplotype analysis of the polymorphic human vascular endothelial growth factor gene promoter. Cancer Research 63 812–816.[Abstract/Free Full Text]

Stoner M, Wormke M, Saville B, Samudio I, Qin C, Abdelrahim M & Safe S 2004 Estrogen regulation of vascular endothelial growth factor gene expression in ZR-75 breast cancer cells through interaction of estrogen receptor alpha and SP proteins. Oncogene 23 1052–1063.[CrossRef][Web of Science][Medline]

Thomas T, Rhodin J, Clark L & Garces A 2003 Progestins initiate adverse events of menopausal estrogen therapy. Climacteric 6 265–267.[Web of Science][Medline]

Toi M, Hoshina S, Takayanagi T & Tominaga T 1994 Association of vascular endothelial growth factor expression with tumor angiogenesis and with early relapse in primary breast cancer. Japanese Journal of Cancer Research 85 1045–1049.[CrossRef][Web of Science]

Toi M, Inada K, Hoshina S, Suzuki H, Kondo S & Tominaga T 1995a Vascular endothelial growth factor and platelet-derived endothelial cell growth factor are frequently coexpressed in highly vascularized human breast cancer. Clinical Cancer Research 1 961–964.[Abstract]

Toi M, Inada K, Suzuki H & Tominaga T 1995b Tumor angiogenesis in breast cancer: its importance as a prognostic indicator and the association with vascular endothelial growth factor expression. Breast Cancer Research and Treatment 36 193–204.[CrossRef][Web of Science][Medline]

Umekita Y, Ohi Y, Sagara Y & Yoshidat I 2002 Expression of maspin predicts poor prognosis in breast-cancer patients. International Journal of Cancer 100 452–455.[CrossRef][Web of Science][Medline]

Uray IP, Liang Y & Hyder SM 2004 Estradiol down regulates CD36 expression in human breast cancer cells. Cancer Letters 20 101–107.

Wang TN, Qian XH, Granick MS, Soloman MP, Rothman VL, Berger DH & Tuszynski GP 1996 Inhibition of breast cancer progression by an antibody to thrombospondin-1 receptor. Surgery 120 449–454.[CrossRef][Web of Science][Medline]

Wedam SB, Low JA, Yang SX, Chow CK, Choyke P, Danforth D, Hewitt SM, Berman A & Steinberg SM 2006 Antiangiogenic and antitumor effects of bevacizumab in inflammatory and locally advanced breast cancer patients. Journal of Clinical Oncology In Press.

Weidner N, Semple JP, Welch WR & Folkman J 1991 Tumor angiogenesis and metastasis-correlation in invasive breast carcinoma. New England Journal of Medicine 324 1–8.[Abstract]

Weidner N, Folkman J, Pozza F, Bevilacque P, Allred EN, More DH, Meli S & Gasparnini G 1992 Tumor angiogenesis: a new significant and independent prognostic indicator in early-stage breast carcinoma. Journal of the National Institutes of Cancer 84 1875–1887.

Woolard J, Wang WY, Bevan HS, Qiu Y, Morbidelli L, Pritchard-Jones RO, Cui TG, Sugiono M, Waine E, Perrin R et al. 2004 VEGF165b, an inhibitory vascular endothelial growth factor splice variant: mechanism of action, in vivo effect on angiogenesis and endogenous protein expression. Cancer Research 64 7822–7835.[Abstract/Free Full Text]

Writing Group for the Women’s Health Initiative Investigators 2002 Risks and benefits of estrogen plus progestin in healthy postmenopausal women: principal results from the women’s health initiative randomized controlled trial. Journal of the American Medical Association 288 321–333.[Abstract/Free Full Text]

Wu J, Richer J, Horwitz KB & Hyder SM 2004 Progestin-dependent induction of vascular endothelial growth factor in human breast cancer cells: preferential regulation by progesterone receptor B. Cancer Research 64 2238–2244.[Abstract/Free Full Text]

Wu J, Brandt S & Hyder SM 2005a Ligand- and cell-specific effects of signal transduction pathway inhibitors on progestin-induced vascular endothelial growth factor levels in human breast cancer cells. Molecular Endocrinology 19 312–326.[Abstract/Free Full Text]

Wu J, Liang Y, Nawaz Z & Hyder SM 2005b Complex agonist-like properties of ICI 182,780 (Faslodex) in human breast cancer cells that predominantly express progesterone receptor-B: implications for treatment resistance. International Journal of Oncology 27 1647–1659.[Web of Science][Medline]

Yamamoto Y, Toi M, Kondo S, Matsumoto T, Suzuki H, Kitamura M, Tsuruta K, Taniguchi T, Okamoto A & Mori T 1996 Concentrations of vascular endothelial growth factor in the sera of normal controls and cancer patients. Clinical Cancer Research 2 821–826.[Abstract]

Yazidi IE, Renaud F, Laurent M, Courtois Y & Boilly-Marer Y 1998 Production and estrogen regulation of FGF1 in normal and cancer breast cells. Biochimica Biophysica Acta 1403 127–140.[Medline]

Zetter RR 1998 Angiogenesis and tumor metastasis. Annual Reviews in Medicine 49 407–424.

Zhang HT, Craft P, Scott PA, Ziche M, Weich HA, Harris AL & Bicknell R 1995 Enhancement of tumor growth and vascular density by transfection of vascular endothelial cell growth factor into MCF-7 human breast carcinoma cells. Journal of the National Cancer Institute 87 213–219.[Abstract/Free Full Text]

Zhang HT, Scott PA, Morbidelli L, Peak S, Moore J, Turley H, Harris AL, Ziche M & Bicknell R 2000a The 121 amino acid isoform of vascular endothelial growth factor is more strongly tumorigenic than other splice variants in vivo. British Journal of Cancer 83 63–68.[CrossRef][Web of Science][Medline]

Zhang M, Volpert O, Shi YH, Peak S, Moor J, Turley H, Harris AL, Ziche M & Bicknell R 2000b Maspin is an angiogenesis inhibitor. Nature Medicine 6 196–199.[CrossRef][Web of Science][Medline]

Zhang W, Ran S, Sambade M, Huang X & Thorpe PE 2002 A monoclonal antibody that blocks VEGF binding to VEGFR2 (KDR/Flk-1) inhibits vascular expression of Flk-1 and tumor growth in an orthotopic human breast cancer model. Angiogenesis 5 35–44.[CrossRef][Medline]

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