Breast cancer is divided into three subtypes based on chemotherapeutic sensitivity: (1) estrogen receptor-positive (ER+); (2) overexpressing human epidermal growth factor receptor 2 (HER2+), which can be ER+ or ER− and (3) triple-negative (TN), which lacks estrogen, progesterone, and HER2 receptor expression [5]. The gene discussed is ERBB2; the disease is breast cancer.