In 64 PCNSL patients, programmed death-ligand 1 (PD-L1) was expressed in 4.1% of PCNSL tumors and 52% of surrounding tissues, and was correlated with interferon (IFN)-γ and CD4 expression in PCNSL cells and microenvironments, respectively22. This evidence concerns the gene CD274 and primary central nervous system lymphoma.