The suppression of tumor suppressor genes, such as p53, phosphatase and tensin homolog (PTEN) and pVHL, may increase the expression of HIF-1α in tumor cells, as well as the action of oncogenes [including ras, SRC and phosphatidylinositide 3 kinase (PI3K) proteins), growth factors (such as the endothelial growth factor) and cytokines (including prostaglandin E2) (12). Here, PTEN is linked to neoplasm.