PDCD1 and central nervous system cancer: Since then, a diverse set of biomarkers have been implicated as prognostic indicators in gliomas, including checkpoint molecules (PD-1, CTLA-4, TIM-3) [26,27,28], growth/angiogenesis proteins (EGFR) [29], and cytokines (TGF-β, IL-4, IL-13) [30,31].