HER2-low-positive tumors came into clinical consideration as a new category of breast cancer when fam-trastuzumab deruxtecan-nxki (T-DXd), a novel ADC, was found to be associated with significant progression-free survival in comparison with the physician’s choice of chemotherapy in patients with pretreated metastatic HER2-low-positive breast cancer [10,11]. This evidence concerns the gene ERBB2 and breast carcinoma.