Representative images of FOXP1 immunostaining demonstrate the 3 groups of DLBCLs classified according to FOXP1 expression. Standard streptavidin ABC immunocytochemistry with heat-mediated antigen retrieval was used, with DAB as the chromogen. FOXP1 is visualized in brown. The blue nuclear counterstain is hematoxylin. (A) FOXP1 negative. Occasional cells have very weak expression of FOXP1 (arrow). (B) FOXP1 variable; weak positive. Approximately 50% of the cells express FOXP1 with variable intensity. (C) FOXP1 uniform high expression. One hundred percent of tumor cells show strong, uniform expression of FOXP1. Small lymphocytes are negative (arrows). All images were captured at 60 × magnification using an Olympus Bx50 microscope (Olympus, Tokyo, Japan), a Plan Apo 60×/1.40 oil objective lens (Tokyo, Japan), a Leica DFC-320 digital camera (Leica, Solms, Germany), and associated Leica IM50 software.