In contrast, colon tumor xenografts showing either a low expression of the target NG2 on the tumor vessels (KM12L4; data not shown), or higher expression, however without clear colocalization to CD31+ endothelial cells indicating blood flow-allowing microvessels (HTB38; data not shown), did not respond with tumor growth retardation to systemic tTF218-TAA (data not shown). This evidence concerns the gene PECAM1 and neoplasm.