Even though imaging of endogenous markers of hypoxia, such as carbonic anhydrase IX (CAIX) and vascular endothelial growth factor (VEGF), has been employed for this purpose, hypoxia-specific positron-emission tomography (PET) radiotracers have the advantage of directly reflecting tumor oxygen levels rather than hypoxia-mediated changes in phenotype [5]. This evidence concerns the gene CA9 and neoplasm.