Protein CIP2A also known as cancerous inhibitor of PP2A (CIP2A) is a protein that in humans is encoded by the KIAA1524 gene. Protein phosphatase 2A (PP2A) is a cellular tumor suppressor which inhibits cell proliferation and transformation of normal cells to malignant cancer cells. Inhibition of PP2A activity is a prerequisite for human cell transformation. However, the in vivo mechanisms by which PP2A activity is inhibited in spontaneously transformed human cancer cells have been unclear.