The breast cancer prognosis and treatment response are affected by a variety of factors, including the presence of the estrogen receptor (ER), the progesterone receptor (PR), human epidermal growth factor receptor 2 (HER2/neu), tumor histological grade, type, and size, and the lymph node metastasis (Al-Thoubaity, 2020). The gene discussed is ESR1; the disease is breast cancer.