CA9 and colon carcinoma: Althougha strong correlation exists between CAIX expression and hypoxia, discrepanciescan also be found in human tumors.40−42 This disparity makesCAIX imaging unsuitable for hypoxia assessment in some tumor models.For instance, MC38 colon carcinoma cells show the highest in vitro CAIX inducibility, but in vivo CAIX expression is very low.43 The absenceof CAIX in MC38 tumor tissue suggests that hypoxia kinetics are importantfor the induction of CAIX.