CA9 and cancer: Hypoxia-driven expression of multidrug resistance (MDR1, formally ABCB1) [10], retinoic acid receptor-related orphan receptor α4 (RORA) [11], basigin (CD147, formally BSG) [12], carbonic anhydrase 9 (CA9) [13,14] and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) [15] gene loci falls into this mechanistic category, at least in some cancer cell types.