CA9 and breast cancer: 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.