HIF1A and neoplasm: Metformin potentially ameliorates hypoxia in the tumor microenvironment through its potential effect on mitochondrial function and downstream oxygen production, and it has been reported that metformin can cause the degradation of oxygen-dependent hypoxia inducible factor 1α (HIF-1α) in hepatocellular carcinoma cells, thus improving the phenotype of the inhibitory tumor microenvironment caused by hypoxia [35].