Several mechanisms of immune-escape have been identified in malignant tumors, including the aberrant expression of immune costimulatory ligands, such as those of the B7 family, namely programmed cell-death protein 1 (PD-1) (also known as B7-H1) and its ligands, programmed cell-death ligand 1 and 2 (PD-L1 and PD-L2). This evidence concerns the gene PDCD1 and cancer.