Figure 4B showed that IL-6 silencing vector attenuated angiogenesis demonstrated by the staining of CD31 and VEGF. To further examined whether circulating IL-6 facilitating the induction of angiogenesis, an intraperitoneal injection of IL-6 (60 or 100 ng per mouse, 3 times per week) was started one day before tumor implantation. As shown in Figure 4C, IL-6 triggered angiogenesis and endothelial tube formation within the tumor by the staining of VEGF, MMP-9 and CD31 in mice bearing tumors for 2 weeks. This evidence concerns the gene PECAM1 and neoplasm.