Alteration of gene expression in tumors owing to hypoxia. The hypoxic conditions inside a tumor mass lead to the activation of the hypoxia-inducible transcription factor (HIF-1), which induces metabolic adaptation (an increase in glycolytic enzymes) and activates angiogenic factors that stimulate the growth of new blood vessels.

[Information from C. V. Dang and G. L. Semenza, Trends Biochem. Sci. 24:68–72, 1999.]