Carbonic anhydrase IX (CA9) is a tumor marker responsible for the reversible hydration of carbon dioxide (CO2) to release protons (H+) and bicarbonate ions (HCO3−), regulating both intra‐ (pHi) and extracellular (pHe) pH balance and contributing to the hypoxic and acidic tumor microenvironment.[9] CA9 inhibitors are widely used to suppress tumor growth and metastases,[10] but their use in OA treatment has not been reported. This evidence concerns the gene CA9 and neoplasm.