ERBB2 and breast cancer: Breast cancer is categorized into three major subtypes based on the presence or absence of molecular markers for estrogen, progesterone, and human epidermal growth factor 2 (ERBB2, also known as HER2) receptors: hormone receptor positive/HER2 negative (70% of patients), HER2 positive (15–20%), and triple-negative (TNBC, tumors lacking all three standard molecular markers; 15%) [4,5].