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An 89-year-old woman with recurrent hormone receptor-positive and HER2-negative breast cancer was treated with fulvestrant-palbociclib combination therapy. However, 3 months after therapy initiation, she presented to our emergency room with dyspnea and fever and was admitted to our hospital because of respiratory failure. After radiological and microbiological evaluation, she was diagnosed with palbociclib-related pneumonitis. Accordingly, corticosteroids were administered, and the patient exhibited initial clinical and radiological improvement. However, pneumonitis recurred following corticosteroid tapering; her condition did not improve with high-dose intravenous corticosteroid administration, leading to death. Palbociclib- related pneumonitis is rare, but clinicians need to pay attention to this potentially lethal adverse event.