According to the 2018 American Society of Clinical Oncology (ASCO)/College of American Pathologists (CAP) guidelines, breast cancer is classified as HER2-positive when HER2 expression is scored as 3+ by immunohistochemistry (IHC) or 2+ IHC with gene amplification by reflex in-situ hybridization (ISH) (Wolff et al., 2018). This evidence concerns the gene ERBB2 and breast cancer.