Hypoxia, defined as reduced oxygen tension, is a common physiological
phenomenon in both normal embryonic development and malignancy
progression. Although severe hypoxia is generally toxic for both normal
tissue and tumors, neoplastic cells gradually adapt to prolonged hypoxia
though additional genetic and genomic changes with a net result that
hypoxia promotes tumor progression and therapeutic resistance. Hypoxia
promotes cancer progression by regulating various aspects of cancer
biology, including radiotherapy resistance, metabolism, angiogenesis and
invasion/migration.