Expression of programmed cell death ligand‐1 by immune cells in the microenvironment is a favorable prognostic factor for primary diffuse large B‐cell lymphoma of the central nervous system

Primary diffuse large B‐cell lymphoma (DLBCL) of the central nervous system (PCNS‐DLBCL) is rare. Thirty‐nine patients consecutively diagnosed as having PCNS‐DLBCL were analyzed to highlight the prognostic value of the expression of programmed cell death ligand‐1 (PD‐L1) by neoplastic cells and immune cells in the microenvironment. They were positive for CD20 in all (100%), CD5 in two (5%), CD10 in nine (23%), BCL‐2 in 27 (69%), BCL‐6 in 34 (87%), and MUM‐1 in 37 (95%). Only one case was positive for neoplastic PD‐L1, with an unexpectedly long clinical course of 92 months. The remaining 38 cases were further divided into three groups based on the percentage of PD‐L1+ cells among microenvironmental immune cells. Cutoffs of