Based on the DESTINY-Breast04 trial, T-DXd was recently approved for patients with unresectable/metastatic HER2-low (IHC 1+ or IHC 2+ and HER2 ISH-negative) breast cancer who have either received one line of chemotherapy in the metastatic setting or progressed within 6 months of adjuvant chemotherapy [19]. This evidence concerns the gene ERBB2 and breast cancer.