HIF1A and neoplasm: The status of hypoxia upgrade the level of VEGF in response to a tumor microenvironment via the hypoxia-inducible transcription factor-1α (HIF-1α) and peroxisome proliferator-activated receptor-gamma coactivator (PGC-1α), Expression of VEGF in response to hypoxia is key to this process and has led to VEGF being defined as the prime hypoxia-inducible angiogenic factor [25, 26].