To the Editor: In the DESTINY-Breast04 trial, involving patients with metastatic breast cancer expressing low levels of human epidermal growth factor receptor 2 (HER2), Modi et al. (July 7 issue)1 found that treatment with trastuzumab deruxtecan resulted in an impressive 52.3% of patients having a response, as well as in longer progression-free survival and overall survival than the physician’s (protocol-limited) choice of chemotherapy. These results have led to great enthusiasm in the field of oncology, and patients will have high expectations. Approval of trastuzumab deruxtecan for the treatment of HER2-low advanced breast cancer would greatly increase the indication for the . . .