CA9 and neoplasm: In previous studies on CAIX expression in HCT116 spheroids, the extracellular acidification was accompanied by an intracellular alkalinisation.11 We therefore hypothesised that if extracellular acidification by CAIX activity was due to a transmembrane redistribution of acidity, the intracellular compartment of CA9 tumours would be more alkaline than that of the EV tumours.