A phase Ib study of 54 patients (NCT02564900) explored the efficacy and safety of T-DXd) in patients with advanced HER2-low BC, with an ORR of 37% (95% CI, 24.3–51.3%), a median duration of response (DOR) of 10.4 months, a median PFS of 11.1 months, and a median OS of 29.4 months [107]. This evidence concerns the gene ERBB2 and breast cancer.