ERBB2 and breast cancer: Ten to 20% of BC are HER2-positive [2,3], and patients with HER2-positive BC are eligible for targeted therapies directed against HER2 protein; either monoclonal antibodies (MAbs) such as trastuzumab and pertuzumab, or kinase inhibitors such as lapatinib and, more recently, antibody–drug conjugates (ADC) such as trastuzumab deruxtecan.