Breast cancer is categorized into three major subtypes based on molecular markers for estrogen or progesterone receptors and human epidermal growth factor receptor 2 (HER2): hormone receptor (HR)-positive/HER2-negative (70 % of patients), HER2-positive (15–20 %), and triple-negative (tumors lacking all three standard molecular markers; 15 %) [2]. Here, ERBB2 is linked to breast cancer.