CA9 and neoplasm: The accumulated HIF‐α combines with HIF‐β to form a heterodimer, which enters the nucleus and binds to the promoter regions of genes containing hypoxia response elements, thus activating the transcription of downstream genes, including VEGF, PDGF, carbonic anhydrase IX (CAIX), and others, thereby promoting tumor angiogenesis, proliferation, and metastasis.22, 23