Pembrolizumab, a humanized IgG4 PD-1 (programmed cell death 1) antagonist antibody, was recently approved for the treatment of advanced melanoma, non–small-cell lung cancer, and head and neck squamous cell carcinoma. As an immune checkpoint inhibitor (CPI), pembrolizumab has a unique toxic effects profile: CPI-induced sarcoidlike reactions are an emerging immune-related adverse event (irAE).1