PIK3CA and breast cancer: HER2 dimerization and phosphorylation initiate signaling that leads to activation of downstream proteins including phosphoinositide 3-kinases (PI3K), protein kinase B (PKB, also known as AKT), and mammalian target of rapamycin (mTOR), thereby transducing signals for cell proliferation, cell survival, and angiogenesis in various types of cancer, including breast cancer [6, 7].