In the first-in-human phase 1 study of T-DXd, which included 111 patients with heavily pretreated advanced HER2-positive breast cancer, T-DXd monotherapy exhibited a response rate of 59.5% (95% CI, 49.7 to 68.7), with a median duration of response of 20.7 months [14]. This evidence concerns the gene ERBB2 and breast cancer.