– Carbonic anhydrases IX (CA IX), also known as membrane antigen MN or CA9, is a member of the carbonic anhydrase (CA) family and may be involved in cell proliferation and cellular transformation. CAs are zinc metalloenzymes that catalyze the reversible hydration of carbon dioxide (H2O + CO2 = H+ + HCO3–) and thus participate in a variety of biological and physical processes. CA9 is a transmembrane enzyme expressed primarily in carcinoma cells. It is one of the best markers for hypoxia and for RCC. Appears to be a novel specific biomarker for a cervical neoplasia.