BCL-6 protein expression in a case of AIDS-related PCNSL (DLCL). The microphotograph shows that the tumor is relatively monomorphous and predominantly consists of large tumor cells displaying a large noncleaved cell morphology. Several tumor cells display the characteristic nuclear positivity for BCL-6. Paraffin-embedded tissue section, APAAP immunostaining, hematoxylin counterstain. Original magnification × 250.