Drug-induced Interstitial Lung Disease with a Hypersensitivity Pneumonitis Pattern Following Pembrolizumab Plus Epirubicin and Cyclophosphamide Therapy: First Report with Pathological Findings.

We report the first pathologically confirmed case of drug-induced interstitial lung disease (DI-ILD) with hypersensitivity pneumonitis (HP). A 63-year-old woman with triple-negative breast cancer developed a fever and cough 1 week after starting neoadjuvant pembrolizumab plus epirubicin and cyclophosphamide (EC). Chest computed tomography revealed diffuse centrilobular ground-glass opacities, and a cryobiopsy confirmed non-fibrotic HP. Although Krebs von den Lungen-6 levels were normal, surfactant protein-D levels were elevated. The patient's condition improved with drug discontinuation and brief corticosteroid therapy, enabling curative surgery. This presentation may represent a distinct phenotype of EC-induced ILD, underscoring the importance of an early diagnosis.