PIK3CD and neoplasm: Notably, HER2 overexpression promotes tumor-cell proliferation, adhesion, migration, and survival via constitutive activation of cascades in the downstream signaling transduction of two pathways: the Ras/Raf/Mitogen-activated protein kinase (MAPK) pathway and the phosphatidylinositol 3 kinase (PI3K)/AKT/mammalian target of rapamycin (mTOR) pathway [7].