On the basis of results from the randomized phase 3 DESTINY-Breast03 study, T-DXd is approved for the treatment of adult patients with unresectable or metastatic HER2+ breast cancer who have received a prior anti-HER2–based regimen in the metastatic setting or who have received a prior anti-HER2–based regimen in the neoadjuvant or adjuvant setting and developed disease recurrence during or within 6 months of completing therapy20,21. The gene discussed is ERBB2; the disease is breast carcinoma.