PAX5 and primary central nervous system lymphoma: Pathologic evaluation of PCNSL commonly reveals DLBCL characterized by sheets oflarge lymphoma cells that are highly proliferative (demonstrated by high Ki-67expression) with large areas of necrosis that may harbor viable perivascularlymphoma islands.14 PCNSL in non-HIV patients does not tend to show the presence of Epstein Barrvirus or histological changes related to this viral infection.15 The tumor cells in primary CNS DLBCL are positive for B-cell markers (Pax5,CD19, CD20, CD79a) with either kappa or lambda light chain restriction.