Although the U.S. Food and Drug Administration (FDA) has approved pembrolizumab, an ICI targeting PD1, for individuals with TMB-High (defined as ≥10 mutations/Mb) solid tumors (41), evidence showed high TMB failed to predict response to ICIs across all cancer types including breast cancer, prostate cancer, and glioma (42). Here, PDCD1 is linked to central nervous system cancer.