HIF1A and neoplasm: Recent studies suggest that the success of HIF-1 inhibition in vivo may critically depend on other factors of the tumor microenvironment such as glucose metabolism and pH [27,28] and on the ability of any given strategy to eliminate virtually all HIF-1 function as cell mixing experiments described by Williams et al. [21] indicated that 1% of cells with intact HIF-1 function within a tumor are sufficient to preserve tumor growth.