Of course, the possible inclusion of anti-HER2 ADCs in the treatment armamentarium for HER2-low breast cancer is still far from the implementation in the clinical practice, thus limiting the contextualization of our observation in a contemporary clinical scenario, also given the actual lack of solid evidence supporting the adoption of the metastatic breast cancer phenotype rather than that of the primary tumor in the treatment-decision process of advanced disease. This evidence concerns the gene ERBB2 and breast cancer.