CA9 and cancer: Pyruvate decarboxylation within mitochondria causes the generation and subsequent release of CO2, which favors increased expression of carbonic anhydrase IX (CA-IX), a cancer-associated membrane bound isoform of the enzyme carbonic anhydrase that catalyzes the hydration of CO2 to bicarbonate and H+, thus contributing to acidify the extracellular microenvironment of tumors (79, 80).