Fig. 2.

Tumor angiogenesis and vascular structure and function are abnormal. A Normally, a delicate balance between pro-angiogenic factors and anti-angiogenic factors is maintained to strictly closely regulate angiogenesis. But tumor tissue continued to overexpress pro-angiogenic factors, which kept tumor tissue in a pro-angiogenic state. B Hypoxia promotes the overexpression of pro-angiogenic factors in tumors, which will lead to tumor vascular abnormalities, which in turn will reduce oxygen delivery, forming a vicious cycle. C The structure and function of tumor vascular ECs and vascular walls are abnormal, leading to an abnormal TME, and promoting the development and metastasis of tumor. EC endothelial cell, BM basement membrane, CAF cancer-associated fibroblast, EndMT endothelial-mesenchymal transition