The phase 3 DESTINY-Breast04 trial showed T-DXd is associated with an increased rate of ILD or pneumonitis in patients receiving T-DXd (45/371; 12%) relative to those receiving their physician's choice of chemotherapy (1/172; 0.6%) [29], as did the DESTINY-Breast06 trial in patients with HER2-low or HER2-ultralow expressing disease with ILD or pneumonitis in 49/434 (11.3%) of patients receiving T-DXd [28]. This evidence concerns the gene ERBB2 and pneumonitis.