The Tie-2 receptor is ubiquitously expressed in highly vascularized tissues, suggesting that Tie-2 expression is a general feature of all endothelial cells. In addition, Tie-2 expression is up-regulated in various tumors, including hepatocellular carcinoma and colorectal cancer, however, it was also reported to be heterogeneously expressed in vessels of human breast and pancreatic carcinoma.