HER2-mutated breast cancers tend to be multicentric and multifocal with nodal involvement, are more commonly associated with liver metastases than the HR+ breast cancer, and have increased risk of central nervous system relapses particularly if already treated with trastuzumab, a monoclonal antibody binding to the extracellular domain of HER2 [42]. This evidence concerns the gene ERBB2 and breast carcinoma.