Currently, T-DXd is approved in Europe and the United States (US) for the treatment of adult patients with unresectable or metastatic HER2-positive breast cancer who have received at least one (Europe) or two (US) anti-HER2-based regimens [4, 5], based on the results from the DESTINY-Breast03, 02, and 01 trials. This evidence concerns the gene ERBB2 and breast carcinoma.