ESR1 and breast cancer: Gene amplification and over-expression of human erythroblastosis oncogene B (ERBB) up-regulates the HER2 receptor on the surface of breast cancer cells, which further induces the activation of the ER co-activator, amplified in breast cancer 1 (AIB-1)/steroid receptor coactivator-3 (SRC-3), which can reduce the efficacy of tamoxifen therapy [74].