Programmed death 1 (PD-1) is a cell surface co-receptor member of the CD28/CTLA-4 family, and functions as a downregulator of the immune system through a dual mechanism of inhibition (1). PD-1 is expressed on the cell surface of activated T- and B-cells. Anti-tumor immunity may be controlled by the PD-1/PD-L1 signaling pathway. PD-L1, one of the ligands associated with PD-1, provides immunity for tumor cells by inducing apoptosis of activated T cells or by inhibiting cytotoxic T cells (1,2). Therapies that target the PD-1 receptor have shown unprecedented results with high levels of clinical response in patients with various cancer types (2,3). The presence of PD-1 positive tumorinfiltrating lymphocytes (TIL) has been associated with poor prognosis in human breast cancers and may be useful in antibody therapy targeting the PD-1/PD-L1 signaling pathway (1). Treatments targeting PD-1 and its ligand, PD-L1, have also shown encouraging results in melanoma, non-small-cell lung cancer, and renal cell carcinoma (3-5). This antibody can also be used in multiplex stains with other antibodies such as CD4, CD8, FOXP3, cytokeratin and melanoma markers (6).