The extracellular location of the CAIX active site together with its overexpression in hypoxic cancer cells compared to minimal expression in healthy cells, except in the gastro-intestinal tract and the stomach (Pastoreková et al., 1997) makes hypoxia-induced CAIX an accessible target for new anti-cancer therapy (Supuran, 2008; Morris et al., 2011). The gene discussed is CA9; the disease is cancer.