CD34 and neoplasm: Because of exposure to angiogenic factors like VEGFs and FGFs in tumor microenvironment, tumor endothelial cells down-regulate the expression of intercellular cell adhesion molecule-1/2 (ICAM-1/2), vascular endothelial cell adhesion molecule-1 (VCAM-1) and CD34 which are related with leukocyte-vessel wall interactions [44], [45].