Molecular endogenous markers such as HIF-1α, carbonic anhydrase IX (CAIX), glucose transporters 1/3 (GLUT-1/3), vascular endothelial growth factor (VEGF), and monocarboxylate transporter 4 (MCT-1) also play a role in the assessment of tumor hypoxia. The gene discussed is CA9; the disease is neoplasm.