PECAM1 and neoplasm: The role of HIF-1α in SUM149 MFP growth was confirmed by reduced growth of HIF-1α knockdown in SUM149 clones compared to the control clones in vivo, which was accompanied by reduced in the number of CD31 expressing endothelial cells, highlighting the crucial function of HIF-1α in regulating tumor vascularization and angiogenesis [29].