DLL4 and neoplasm: Indeed, inhibition of notch signaling in rodents with inhibitory antibodies directed against the Notch ligand DLL4 leads to tumors in several organs that may be of vascular origin [56], and conditional knockout of notch1 in endothelial cells causes the appearance of vascular proliferations in the liver [19,20], suggesting that NOTCH1 is a tumor suppressor in endothelium.