Anti-estrogen therapy (e.g., tamoxifen, fulvestrant [Faslodex], letrozole) is the first choice for these patients after surgery, whereas chemotherapy is used as the main medical treatment modality for ER-/PR- patients, and HER2-targeted therapy (e.g., trastuzumab [Herceptin]) is used for HER2+ BC [4]. The gene discussed is ESR1; the disease is breast cancer.