DLL4 and neoplasm: While it was reported to act as a negative driver of tumor expansion in tested malignant cell lines grafted in mice [17, 26, 34], Dll4 expression in transduced human glioblastoma, prostate and gastric cancer cell xenografts was associated with promoted tumor growth, to some extent, due to a reduction of tumor hypoxia and apoptosis or increased secretion of matrix metalloproteinase-2 [26, 35].