Programmed Death 1 (PD-1) and Cytotoxic T-lymphocyte Associated Protein 4 (CTLA-4) are immune-inhibitory receptors (immune checkpoints) expressed mainly on T cells, and their inhibition with function-blocking antibodies has been shown to enhance anti-tumor T cell responses (Walker and Sansom, 2011; Kamphorst and Ahmed, 2013). This evidence concerns the gene CTLA4 and neoplasm.