It has been demonstrated that the ADC trastuzumab-emtansine (T-DM1) presents poorer benefits for HER2-low breast cancer, while the novel ADC trastuzumab-deruxtecan (TDXd) showed significant improvements in both progression-free and overall survival in the results of the DESTINY-Breast04 trial [29]. This evidence concerns the gene ERBB2 and breast cancer.