PDCD1 and Merkel cell skin cancer: Currently, there are no FDA-approved anti-PD-1/PD-L1 inhibitors for glioblastoma (119), but the PD-1 inhibitors Pembrolizumab, Nivolumab, Cemiplimab, Retifanlimab by Zynyz (approved under FDA’s Accelerated Approval Program for Merkel cell carcinoma), and Balstilimab (currently in Phase II clinical trials for several cancers), as well as the PD-L1 inhibitor, Atezolizumab, are being tested in clinical trials for safety, tolerability, feasibility and efficacy in newly diagnosed, recurrent and progressive glioblastoma, both as monotherapy and as part of a therapeutic regime (Table 1).