Figure 3.

Mechanisms of angiogenesis in tumors. (A) Sprouting angiogenesis, during which a new vessel branches from an existing vessel. The key biological process involves the balance between the formation of “tip” and “stalk” endothelial cells. (B) Vasculogenesis, during which new blood vessels are generated by endothelial progenitor cells to form networks without the presence of pre-existing vessels. (C) Intussusceptive angiogenesis, which involves the formation of a double lumen and the split of an existing vessel into two new functional blood vessels. (D) Vascular mimicry. Tumor cells form vessel-like structures independently of endothelial cells to facilitate blood flow. (E) Vessel co-option. Tumor cells utilize existing blood vessels for their blood supply. (F) Transdifferentiation. Certain cancer stem cells differentiate into endothelial-like cells and integrate into the vascular structure to support the tumor’s blood supply. RBCs, red blood cells; ECs, endothelial cells; CSCs, cancer stem cells.