Among 245 patients in the pooled analysis who had HER2-positive breast cancer and received 5.4 mg/kg T-DXd every 3 weeks, 15.5% (38 of 245) had drug-related ILD/pneumonitis, with 78.9% of those patients who developed ILD/pneumonitis (30 of 38) having grade 1 or 2 events. This evidence concerns the gene ERBB2 and breast cancer.