CD20 and osteopontin are coexpressed in PCNSL. Dual immunohistochemistry was performed using antibodies specific to CD20 (Dako, Carpenteria, CA) and osteopontin (R&D Systems, Minneapolis, MN). Diaminobenzidine (brown) dye (Dako) was used for CD20 and Vulcan fast red (red) dye (Biocare Medical, Concord, CA) was used for osteopontin. (A) PCNSL. Original magnification ×400. Both CD20 (membranous pattern) and osteopontin (predominantly nuclear) are clearly positive. (B) Second case of PCNSL. Original magnification ×1000. Again, both CD20 and osteopontin are positive. (C) Nodal DLBCL. Original magnification ×400. Only CD20 is positive with no expression of osteopontin. A Leica DMLB optical microscope (Leica Microsystems, Wetzlar, Germany) and Cytoseal-60 mounting media (Richard Allen, Kalamazoo, MI) were used. Images were acquired using a SPOT RT Color Camera (Diagnostic Instruments, Sterling Heights, MI), and were processed with SPOT Advanced program version 2.0 (Diagnostic Instruments) and Adobe Photoshop version 6.0 software (Adobe Systems, San Jose, CA).