PECAM1 and neoplasm: In comparison to normal endothelial cells, tumour-associated endothelial cells show fibroblast-like properties after undergoing an endothelial-to-mesenchymal transition, downregulating the endothelial cell marker CD31 and upregulating the tumour-associated fibroblast markers fibroblast-specific protein 1 (FSP1) and alpha-smooth muscle actin (alpha-SMA) [36].