CA9 and neoplasm: Large amounts of lactate and protons constitute the two byproducts of glycolysis that are expelled out of tumor cells via monocarboxylate transporters (MCT), particularly MCT-1 and MCT-4, and by the action of several carbonic anhydrase (CA) isozymes, with a major role played by a membrane-bound isozyme carbonic anhydrase IX (CA IX) [23,24].