PIK3CA and cancer: The phosphoinositol 3 kinase (PI3K)/ protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is an important signal transduction pathway in regulating the proliferation and apoptosis of cancer cells by participating in cell cycle processes, producing precursor apoptotic proteins, controlling angiogenesis and promoting cancer cell invasion and metastasis [21].