Another study has shown a positive correlation between the expression of an oncogenic pituitary tumor-transforming gene 1 (PTTG1) and that of angiogenic genes (e.g., HIF-α, VEGF, and PDGF-B), cell migrating genes (e.g., MMP2, MMP9, and MMP14), and tumor suppressing genes (e.g., p53 and p21) in glioma cells. This evidence concerns the gene MMP9 and central nervous system cancer.