For patients receiving trastuzumab deruxtecan (T-DXd) monotherapy, the incidence of adjudicated drugrelated interstitial lung disease (ILD)/pneumonitis is 15.4%, according to a study published in ESMO Open. Charles A. Powell, MD, and colleagues conducted a pooled analysis of nine phase 1 and 2 T-DXd monotherapy studies to describe drug-related ILD/pneumonitis. A total of 1,150 patients (44.3%, 25.6%, 17.7%, 9.3%, and 3.0% with breast, gastric, lung, colorectal, and other cancers, respectively) were included in the analysis (median treatment duration, 5.8 months; median of four prior lines of therapy). Most patients experienced low-grade adjudicated drug related ILD/ pneumonitis (grade 1 or 2, 77.4%), and most (87.0%) had their first event within 12 months of the first dose of T-DXd (median, 5.4 months). For 53.2% of events, adjudicated ILD/pneumonitis onset occurred earlier than identified by investigators (median difference in onset, 43 days).