Serine 118 (Ser118) and 167 (Ser167) are two important residues of ERα which have been indicated to be phosphorylated by mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and protein kinase B (AKT), respectively, and appear to be mostly related to BC resistance to tamoxifen (de Leeuw et al., 2011[12]). The gene discussed is ESR1; the disease is breast cancer.