Previous studies have demonstrated the synergistic anti-tumor effect of anti-PD1 antibody in combination with rituximab or temozolomide.11–14 A retrospective analysis has identified high PD-1 expression in tumor infiltrating lymphocytes (TILs) as a significant adverse prognostic factor for PCNSL patients undergoing HD-MTX treatment.22 Our findings suggest that adding PD-1 antibody to the MTR regimen may counteract the adverse prognosis associated with PD-1/PD-L1 pathway. Here, PDCD1 is linked to primary central nervous system lymphoma.