Clinically, based on the expression of molecular indicators, such as estrogen (ER), progesterone (PR), human epidermal growth factor receptor 2 (HER2), and Ki-67, breast cancer is divided into the following types: luminal A, luminal B (HER2-negative), luminal B (HER2-positive), and HER2-positive (Yeo and Guan, 2017). The gene discussed is ERBB2; the disease is breast cancer.