Although it has been suggested that REL is the critical target gene of 2p12-16 amplification in diffuse large B-cell lymphoma (DLBCL), little experimental evidence supports this notion. In the present study, we sought to evaluate the relationship between REL amplification and REL function in a panel of 46 newly diagnosed DLBCLs and to correlate with DLBCL subgroups as identified by gene expression profiles and clinical features. The results indicate that amplification of the REL locus is not associated with accumulation of the active form of REL, as evaluated by immunofluorescence analysis. Upon subgrouping of the DLBCL cases based on gene expression signatures, REL amplification was detected in all subgroups, while high levels of nuclear-located REL were more frequently detected in activated B-cell-like DLBCL. Correlative analyses of REL copy number and REL nuclear accumulation with clinical parameters did not reveal any significant associations. Together these results indicate that 2p12-16 amplification does not lead to abnormal REL activation, suggesting that REL may not be the functional target of the amplification event. Nonetheless, these data indicate that DLBCLs are heterogeneous with respect to REL and thus nuclear factor-kappaB (NF-kappaB) activity.