Nivolumab is an immune checkpoint inhibitor specific to the programmed death 1 (PD-1) receptor. Nivolumab has shown clinical responses in many malignancies. Although immune-related adverse events (irAEs) associated with nivolumab are largely tolerable, severe irAEs have occurred in some patients. | Severe colitis after PD-1 blockade with nivolumab in advanced melanoma patients Potential role of Th1-dominant immune response in immune-related adverse events Two case reports