In fact, increased expression of PD-1 ligands by cancer cells, arising from either genetic alteration or microenvironmental triggers, and their binding to PD-1 receptors on the surface of T cells has been shown to attenuate T-cell receptor (TCR)-mediated signaling and result in an exhausted T-cell phenotype that can prevent lysis of tumor cells2,3. This evidence concerns the gene PDCD1 and neoplasm.