Despite the fact that CA IX is not upregulated in all cancer cell lines [4], a variety of spontaneously arising human tumors, including CNS, head & neck, lung, breast, colon, cervical, ovarian, prostate, renal cancers, leukemia, and melanoma are known to upregulate CA IX expression, making this molecule a clinically relevant biomarker for hypoxic tumors. This evidence concerns the gene CA9 and cancer.