In August 2022, the FDA approved T-DXd also for the treatment of patients with unresectable or metastatic HER2-low (immunohistochemistry [IHC] IHC 1+ or IHC 2+ with a negative in situ hybridization test [ISH−]) breast cancer, who had received prior chemotherapy in the metastatic setting or developed disease recurrence during or within 6 months of completing adjuvant chemotherapy. The gene discussed is ERBB2; the disease is breast cancer.