PIK3CA and cancer: The ER signaling pathway, the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) signaling pathway, the mitogen-activated protein kinase (CDK) 4/6-retinoblastoma (RB) pathway, the tumor protein p53 (TP53)/mouse double minute 2 homolog (MDM2) pathway and growth factor-receptor signaling pathways may be altered in luminal cancers that express the ER.