PDCD1 and metastatic melanoma: Immune checkpoint inhibitors such as anti-cytotoxic T-lymphocyte antigen 4 (CTLA-4) and anti-programmed cell death-1 (PD-1) antibodies, which are now considered first-line therapies in patients with metastatic melanoma, can reverse the immunosuppressive effects exerted by cancer cells and promote antitumor immunity [1-4]. Despite therapeutic advances with IT, patient outcomes can still be improved as responses tend to be limited to a subset of patients who have preexisting T-cell responses that can be reactivated by immune checkpoint blockade [5].