CA9 and cancer: At present, there are three main modalities to assess hypoxia in human cancer patients; nuclear imaging using PET/CT with nitroimidazole compounds such as EF5 or pimonidazole, immunostaining with markers such as hypoxia inducible factor 1 alpha (HIF-1α), downstream HIF-1α targets (e.g. CAIX, VEGF), and transcriptomic analyses based on gene expression signatures of hypoxia4.