The importance of HER2 amplification status as a prognostic marker in BC led to the development and approval of various antibody-based drugs targeting HER2 such as trastuzumab, which today remains the mainstay for treatment of ERBB2/HER2-amplified primary BC, and has cemented HER2 status as a vital treatment-predictive biomarker4,5. This evidence concerns the gene ERBB2 and breast cancer.