CA9 and colorectal carcinoma: We performed IF and IHC staining of the hypoxic marker protein HIF1α and carbonic anhydrase 9 (CA9)20 in sections of human primary CRC tissues and found that the cells expressing increased levels of HIF1α and CA9 were far from the blood vessels; however, the cells expressing decreased levels of HIF1α and CA9 were closer to the blood vessels (Figs. 2a and S2A, B).