Hypoxia-induced due to excessive tumour metabolism and growth produce optimal conditions for the production of pro-angiogenic factors like Vascular Endothelial Growth Factors (VEGFs), Platelet Derived Growth Factors (PDGFs), Angiopoietins, Matrix Metalloproteinases (MMP-2, 9), Interleukins (IL-1, 6, 10), Integrins and overexpression of such proteins activate the angiogenic switch in Tumor Endothelial Cells (TECs). The gene discussed is IL1B; the disease is neoplasm.