PDCD1 and neoplasm: Cytotoxic T cells demonstrate clinically significant anti-tumor activity in melanoma.17 Infiltration of CD8+, generally associated with improved survival, is a good prognostic marker.18 The programmed cell death 1 (PD-1) immune inhibitory receptor is present on T- and B-lymphocytes, natural killer cells, and myeloid cells, and PD-L1 is its corresponding ligand expressed on tumor cells, T and B cells, macrophages, and dendritic cells.19 The PD-1/PD-L1 interaction is a recognized mechanism whereby malignant cells evade the immune system to allow tumor growth and progression.