Although the molecular mechanisms are yet to be elucidated, the reduced intra-tumor microvascular density could facilitate hypoxia mediated triggering of HIF-1α/VEGF pathways which, in combination with extracellular matrix remodeling due to the activation of MMPs, results in tumor growth and angiogenesis, thus making the pituitary tumor prone to apoplectic events. This evidence concerns the gene VEGFA and neoplasm.