The amplification of ERBB2 leads to an overexpression of HER2 promoting cancer cells survival, growth, migration and proliferation through the activation of the RAS/RAF/mitogen-activated protein kinase (MAPK) and the phosphatidylinositol-3 kinase/protein kinase-B/mammalian target of rapamycin (PI3K/AKT/mTOR) signalling pathways. The gene discussed is PIK3CA; the disease is cancer.