PECAM1 and neoplasm: In the view of fact that HER2-targeted therapy can directly suppress angiogenesis by inhibiting vascular endothelial growth factor (VEGF) expression [53, 54], we speculated that scFv-9R/HER2si-mediated HER2 silencing might induce tumor cell apoptosis partially by hindering the process of vascularization in nude mice model, since HER2 expression status in xenografted tumors correlate to tumor microvessel density measured by CD31 immunohistochemistry.