In fact, approximately 60% of patients with a human epidermal growth factor 2 (HER2)-negative BC diagnosis have tumors with low HER2 expression (HER2-low status), defined as an immunohistochemistry (IHC) score of 1 + or 2 + and a negative in situ hybridization (ISH) score [2–4]. Here, ERBB2 is linked to breast cancer.