PTEN and gastric cancer: Loss of PTEN in gastric cancer promotes tumor angiogenesis and invasion by increasing expression of VEGF through the increase of the HIF-1α protein level, which is an active process that requires the degradation of the extracellular matrix, the increase of microvascular permeability both in the blood and lymphatic vessels, and interstitial fluid pressure (IFP) [27], favoring the progression of the intravasation and extravasation of tumor cells.