For instance, in a phase 2 study including 184 patients treated with T-DXd (5.4 mg/kg) for HER2-positive metastatic breast cancer, the incidence of drug-related pneumonitis was reported to be 13.6% for all grades, with grade 3 or higher events occurring in approximately 2.7% of patients, including four deaths felt to be attributable to pneumonitis [17]. This evidence concerns the gene ERBB2 and pneumonitis.