ERBB2 and breast cancer: Cardiotoxicity is known to be a serious side effect in patients with breast cancer who are treated with HER2-targeted therapies including trastuzumab [33–35]; however, the incidence of cardiotoxicity in patients with gastric or breast cancer treated with T-DXd appears to be low and was not observed in the DESTINY-Gastric01 trial [9, 31].