PDCD1 and melanoma: Pembrolizumab, sold under the brand name Keytruda (Merck & Co., Inc., Rahway, NJ, USA), is an FDA-approved immune checkpoint inhibitor directed against the program cell death protein 1 (PD-1) and is currently being used in a vast variety of malignancies such as melanoma, non-small cell lung cancer, and Hodgkin lymphoma [1].