PDCD1 and melanoma: Among immune checkpoint inhibitors, cytotoxic T-lymphocyte-associated protein-4 (anti-CTLA4; ipilimumab) and programmed cell death protein-1 (anti-PD-1; pembrolizumab, nivolumab) antibodies have revolutionized the management of advanced melanoma by showing tumor regression in nearly 50% of patients, compared to less than 10% in the past [17].