PIK3CA and breast cancer: It is well documented that activation of a variety of signaling pathways play critical roles in breast cancer metastasis, such as phosphoinositide-3-kinase (PI3K) pathway, mitogen-activated protein kinase (MAPK) pathway, transforming growth factor (TGF)-β/Smad pathway and vascular endothelial growth factor (VEGF) pathway [5–8].