Not only is lactate transport in cancer cells facilitated by extracellular CAIX, but also by intracellular CAII.184 CAII was found to physically interact with MCT1 in MCF-7 breast cancer cells, as shown by PLA.184 Knockdown of CAII, but not inhibition of catalysis, decreased lactate transport in normoxic and hypoxic MCF-7 breast cancer cells and reduced cell proliferation.176,184 These results indicate that efficient lactate efflux from cancer cells requires both intracellular and extracellular CAs. This evidence concerns the gene CA2 and breast carcinoma.