Cross section of a human breast cancer tumor. This drawing (from Cameron et al. ) depicts a cross section of a human breast cancer tumor. The tumor has a well vascularized capsule. An outer cortex underlies the capsule for 100 to 150 μm. Immunohistochemistry shows that a hypoxia inducing factor HIF-α rich subcortical region is present at distances greater than 100 to 150 μm from blood vessels. The HIF producing region is thought to produce vascular endothelial growth factors causing an observed sprouting of endothelial cell pseudopods and neo-angiogenesis. Cells further away from this neo-angiogenesis zone lack essential nutrients and oxygen and become necrotic. Thus this angiogenesis process is proposed to be hypoxia driven and is also proposed to be a main target of therapeutic EMF therapy.