CA9 and neoplasm: CA IX is overexpressedin many tumors under hypoxic conditions,contributing to tumor acidosis by regulating pH and facilitating thedevelopment of metastatic traits.11,12 Similarly,CA XII is coexpressed with CA IX in various tumors and is highly expressedin cancers, including lung cancer and colorectal cancer.13 Both CA IX and CA XII are present in the cellmembranes of tumor tissue, although their expression can vary, withsome examples expressing only one or both isoforms.14,12