HIF1A and neoplasm: DLL4 is a key ligand that can activate Notch signaling through the HIF-1α-mediated regulatory pathway, regulating cell stemness and differentiation and forming a positive regulation with the HIF pathway to synergistically promote the formation of abnormal vascular networks and tumor invasion and metastasis, which has been confirmed in malignancies, including lung and colorectal cancer (Figure 1).