Supplementary Material for: Palbociclib-Induced Interstitial Lung Disease in Metastatic Breast Cancer: A Case Report and Clinical Considerations

Background: The treatment landscape of hormone receptor-positive, HER2-negative metastatic breast cancer (BC) has been transformed with the advent of cyclin-dependent kinase 4/6 inhibitors (CDK 4/6i). While myelosuppression is the most common adverse effect, interstitial lung disease (ILD) has emerged as a rare but potentially severe complication in real-world settings. Case Presentation: A 76-year-old woman with metastatic HR+/HER2-negative BC developed ILD after prolonged exposure to palbociclib. Treatment discontinuation and high-dose corticosteroids resulted in symptomatic and radiological improvement. Discussion: ILD is an underrecognized but clinically significant toxicity of CDK 4/6i, requiring early diagnosis and prompt intervention to prevent severe respiratory compromise. A high index of clinical suspicion, prompt diagnosis, and rapid treatment strategies are crucial, particularly in elderly patients, to minimizing ILD-associated risks and complications. Further research is needed to establish predictive biomarkers and optimize management guidelines for CDK 4/6i-induced ILD.