Contrary to traditional immunotherapies, such as interferon-α and interleukin 2, which are associated with excessive toxicity, modern immunotherapies, such as antibodies against programmed cell death protein 1, programmed death-ligand 1, or cytotoxic T-lymphocyte-associated protein 4, disable the ability of tumor cells to evade the immune system without any significant side effects [33,34,35]. Here, PDCD1 is linked to neoplasm.