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

Introduction: The treatment landscape of hormone receptor-positive, HER2-negative (HR+/HER2-) metastatic breast cancer (BC) has been transformed with the advent of cyclin-dependent kinase 4/6 inhibitors (CDK4/6i). 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- BC developed ILD after approximately 20 months of palbociclib therapy. Treatment discontinuation and high-dose corticosteroids resulted in symptomatic and radiological improvement. A concomitant pneumomediastinum was considered a secondary manifestation of ILD. Conclusion: ILD is an underrecognized but clinically significant toxicity of CDK4/6i, 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 minimize ILD-associated risks and complications. Further research is needed to establish predictive biomarkers and optimize management guidelines for CDK4/6i-induced ILD.