AKT1 and breast cancer: These three sites have been demonstrated to be phosphorylated by extracellular signal-regulated kinase/mitogen-activated protein kinase (ERK/MAPK), protein kinase B (Akt) and protein kinase A (PKA) and/or p21-activated protein kinase (Pak1), respectively, and appear to be the most relevant sites with regard to breast cancer resistance to tamoxifen (4).