Trastuzumab deruxtecan (T-DXd) is a HER2-targeted ADC approved for the treatment of previously treated HER2-positive (HER2+) metastatic gastric adenocarcinoma or GEJA, metastatic NSCLC with activating HER2 mutations, HER2+ breast cancer, and HER2-low breast cancer. This evidence concerns the gene ERBB2 and breast cancer.