Trastuzumab deruxtecan is indicated for patients with inoperable or metastatic HER2-positive breast cancer who have previously undergone at least two anti-HER2 therapy regimens, and its black box warnings are related to interstitial lung disease and embryotoxicity (Abuhelwa et al., 2022; Hacker, 2020; Keam, 2020). The gene discussed is ERBB2; the disease is breast cancer.