**2. Angiogenesis in HCC**

In HCC, tumor angiogenesis leads to a pathologic vascularization pattern, of which intratumoral vascularization is critical for the diagnosis and treatment of HCC, as well as for pathogenesis and patient prognosis [1, 8, 9]. In general, HCC is supplied with blood flow primarily via the hepatic arteries, while noncancerous lesions and the normal liver parenchyma are supplied predominantly by the portal vein. This distinct vascularization is clinically utilized to diagnose HCC radiographically by emphasizing the tumor lesions. Any tumor mass more than 1–2 mm3 depends entirely on the formation of a vascular network that provides the growing tumor with oxygen and essential nutrients [10].

Of the various proangiogenic factors, vascular endothelial growth factor (VEGF) is one of the most potent and required for both physiological and pathological angiogenesis [11]. VEGF induces EC proliferation, promotes migration and differentiation as well as stimulates permeabilization of blood vessels and vasculogenesis. The several forms of VEGF bind to

two tyrosine kinase receptors, *fms*-like tyrosine kinase (flt-1: VEGFR-1) and the kinase insert domain-containing receptor/murine homolog, fetal liver kinase-1 (KDR/Flk-1: VEGFR-2) [11, 12]. Recent reports have demonstrated that upregulated VEGF expression is more frequently observed in the tumor lesions of HCC than noncancerous lesions [13–15]. Moreover, the marked increase of VEGF expression is shown during both hepatocarcinogenesis and HCC growth in accordance with the augmented neovascularization. Our basic studies elucidated that monoclonal antibodies (mAb) against both VEGFR-1 and VEGFR-2 ameliorated the HCC development with antiangiogenic activity in rodents [16]. These findings indicate that a blockade of the VEGF-VEGFR axis contributes to the suppressive effect on HCC development.

In tumor neovascularization, VEGF often coordinates with other angiogenic pathways. The angiopoietins (Ang) bind with receptor tyrosine kinases (RTKs) with immunoglobulin-like and EGF-like domains (Tie1 and Tie2). Increased levels of Ang2 promote tumor angiogenesis, metastasis, and inflammation with augmentation of VEGF activity. VEGF-A is also upregulated by interaction with multiple growth factors, including fibroblast growth factor (FGF), insulin-like growth factor-1 (IGF-1), platelet-derived growth factor (PDGF), and the transforming growth factors (TGF) [17]. Tissue hypoxia also stimulates VEGF-A upregulation via the hypoxia-inducible factors (HIF)-1α and HIF-2α [17].
