The involvement of HIF-1 and VEGF has been confirmed in in vivo studies; the HIF-1 inhibitor, YC-1, or a neutralizing antibody against VEGF markedly induced apoptosis in endothelial cells and decreased microvessel density after radiation therapy, resulting in radiosensitizing effects in a tumor growth delay assay [51, 52, 54]. The gene discussed is HIF1A; the disease is neoplasm.