To date, five randomized phase 3 trials of T-DXd in breast cancer patients are underway, for HER2-positive (DESTINY-Breast02, NCT03523585; DESTINY-Breast03, NCT03529110) and HER2-low (DESTINY-Breast04, NCT03734029; DESTINY-Breast06, NCT04494425) metastatic disease, and for HER2-positive primary breast cancer who do not achieve complete response after neoadjuvant therapy (DESTINY-Breast05, NCT04622319). The gene discussed is ERBB2; the disease is breast cancer.