However, cancer cells escape elimination by cytotoxic T cells and suppress the effector function of tumor-specific T cells via numerous co-inhibitors (immune checkpoints such as PD-1, CTLA-4, lymphocyte activation gene 3, T cell immunoglobulin and mucin domain-containing protein 3, and T cell immunoreceptor with Ig and immunoreceptor tyrosine-based inhibitory motif domains). This evidence concerns the gene PDCD1 and cancer.