PDCD1 and metastatic melanoma: For example, in patients with metastatic melanoma, the incidence of adverse events with nivolumab (PD-1 inhibitor) was 82.1%, with 16.3% being grade 3–4 toxicities, compared with 86.2% and 27.3%, respectively, with ipilimumab (CTLA-4 inhibitor)6,7.