Apart from ERα gene (ESR1) mutations, endocrine resistance in advanced breast cancer is also associated with activating HER2 and loss of function NF1 mutations, alterations in other mitogen-activated protein kinase (MAPK) pathway genes including EGFR, KRAS, HRAS, BRAF, and MAP2K1 (MEK1), as well as ER transcriptional regulators such as MYC, CTCF, FOXA1, and TBX3 (44). Here, ERBB2 is linked to breast cancer.