CA9 is an oncogene also know as CA IX, carbonic anhydrase 9 or MN/CA9. The gene encoding an oncoprotein called indifferently membrane antigen MN, MN/CA9 isoenzyme, carbonic anhydrase IX CA9, G250/MN/CA9 or protein G250. It was demonstrated that the level of expression of CA9 in tumor tissue can be used as a predictive marker of response to immunotherapy.