Ravneet K. Dhanoa, Robert W. Gao, Kaitlin W. Qualls, Elsa A. Sutton, Kathryn J. Ruddy, Dean A. Shumway and Robert W. Mutter
Trastuzumab Deruxtecan (T-DXd) and lung radiotherapy have each been independently associated with pneumonitis. We present a case of a patient with metastatic Human Epidermal Growth Factor Receptor 2 (HER2)-low breast cancer who developed pneumonitis following sequential palliative lung radiotherapy and T-DXd. T-DXd was discontinued, and symptoms resolved after corticosteroids. The literature review identified T-DXd-induced pneumonitis rates of 11.4% across all tumor types and 10.8% in seven breast cancer studies, higher than other anti-HER2 therapies. Additional studies should be done to characterize the risk of combining radiotherapy with T- DXd.