The activity of HER2 receptors in turn promotes the signalling of other pathways such as the mitogen-activated protein kinases (MAPKs) or cell components like glycogen synthase kinase-3 (GSK-3) and PI3K/Akt/mTOR pathways, both represented in Figure 1, denoting the importance of signal integration and transduction processes in the progression and development of breast cancer [20–23]. Here, PIK3CA is linked to breast cancer.