Abstract
A man in his 80s with metastatic melanoma presented with progressive dyspnea on exertion and dry cough after 7 cycles of pembrolizumab monotherapy. He was initially treated with antibiotics for community acquired pneumonia; however, his symptoms recurred after 2 weeks, and he developed hydropneumothorax. Pleural fluid, bronchoalveolar lavage fluid, and transbronchial biopsy results were all negative for infection, and he was diagnosed with unilateral immune checkpoint inhibitor pneumonitis, highlighting that the radiographic findings of immune checkpoint inhibitor pneumonitis can be unpredictable and include hydropneumothorax.