In a phase 1 study (NCT02564900) assessing the role of T-DXd for patients with HER2-positive metastatic solid tumors, 115 patients with pretreated breast cancer were included and 17.3% (n = 20) cases of ILD/pneumonitis/organizing pneumonia were reported, including one grade 3 event and two treatment-related deaths due to pneumonitis [32]. This evidence concerns the gene ERBB2 and breast cancer.