PDCD1 and neoplasm: In essence, this study showed that the concept of molecular mimicry which is popular in the autoimmune field can be extended to explain concepts of anti-tumor immunity in the CNS; anti-PD-1 and anti-CTLA-4 therapies are only effective in eliminating intracranial tumors in the context of extracranial disease which provides a source of tumor antigens in the periphery.