Classic histopathologic picture of PCNSL of diffuse large B-cell lymphoma category. Tumor cells (filled arrows) usually grow forming classic perivascular cuffings, are CD20 positive, and express other pan-B-cell markers (CD19, CD20, CD22, CD79a), markers of germinal center B cells (bcl-6; 60%-80% of cases), and markers of late germinal center B cells (MUM1; 90%), while are CD3 negative. A reactive T-cell infiltrate (open arrows) constituted by a perivascular rim of small lymphocytes interposed between vessel (VL) and neoplastic cells is observed in one-third of cases. These lymphocytes are smaller than neoplastic ones, and are CD20 negative and CD3 positive. The presence of this reactive infiltrate is associated with significantly better outcome in patients treated with modern approach.