Trastuzumab Deruxtecan-Induced Pneumonitis: Case Series.

Trastuzumab deruxtecan (T-DXd) is a HER2-targeted antibody-drug conjugate with proven efficacy in metastatic breast cancer, but interstitial lung disease (ILD) and drug-induced pneumonitis are potentially life-threatening toxicities. We retrospectively reviewed three patients with HER2-positive metastatic breast cancer treated with T-DXd at a tertiary hospital in Saudi Arabia who subsequently developed pneumonitis. Pneumonitis developed after 2-9 cycles of T-DXd, presenting with cough, dyspnea, and ground-glass opacities. All patients received corticosteroids and required permanent discontinuation. Early recognition and multidisciplinary management of T-DXd-induced pneumonitis are essential. Clinicians should monitor respiratory symptoms and apply timely corticosteroid therapy.