Pemetrexed-induced Interstitial Lung Disease Mimicking Hypersensitivity Pneumonia: A Pathologically Proven Case

We herein report a 45-year-old woman with lung adenocarcinoma stage IV (cT4N3M1a). She was treated with pemetrexed (PEM) monotherapy following four cycles of first-line treatment with carboplatin, paclitaxel, and veliparib. After three cycles of PEM treatment, she presented with dyspnea, and chest computed tomography showed diffuse ground-glass attenuation (GGA), suggesting hypersensitivity pneumonia (HP). Bronchoalveolar lavage revealed a marked increase in lymphocytes (90.5%), and a transbronchial lung biopsy confirmed lymphocytic alveolitis with granuloma. Because her symptoms and diffuse GGA were spontaneously resolved with PEM discontinuation alone, PEM-induced interstitial lung disease was diagnosed. Chest physicians should be aware that PEM can induce HP-type interstitial lung disease.