ABSTRACT
Hypoxia is the decrease of normal oxygen tension in tissues. It often occurs in the tissues of acute and chronic vascular diseases or lung diseases and cancerous lesions. Severe or persistent hypoxia can lead to the death of cell. The lack of oxygen in the tumor is mainly due to the absence or deficiency of normal tumor blood vessel function, which results in a decrease of the oxygen diffusion function within the tumor, eventually leading to a series of biochemical reactions. Although hypoxia is toxic on tumor cells, tumor cells still have a strong adaptability. In the hypoxic microenvironment of tumors, tumor cells can produce adaptive changes or genetic changes so that the tumor could survive in an oxygen-deficient environment, even proliferate. Finally, tumor progression will happen. This process visualizes malignant phenotype of the tumor and makes them more aggressive. The epithelial mesenchymal transition in the tumor microenvironment plays an important role in tumor cell migration, invasion, malignant progression and metastasis. Hypoxia leads to epithelial-mesenchymal transition in tumor tissue, reconstitution of extracellular matrix in tumors, and induction of resistance to antitumor drugs. There are many researches related to hypoxia and tumors. The research contents are complex. Targeted therapy for hypoxia is receiving more and more attention, but the overlapping of signal molecules due to the related mechanism between hypoxia and tumors. An effective hypoxia-targeted therapeutic drug that can be used clinically which requires hard work and arduous exploration from researchers.