Gene expression profiling has revealed that Diffuse Large B-Cell Lymphoma is composed of at least 3 different sub-groups, each having distinct oncogenic mechanisms that respond differently to therapies. Germinal Center B-Cell like (GCB) DLBCLs appear to arise from normal germinal center B cells, while Activated B-cell like (ABC) DLBCLs are thought to arise from postgerminal center B cells that are arrested during plasmacytic differentiation. The differences in gene expression between GCB DLBCL and ABC DLBCL, are as vast as the differences between distinct types of leukemia, but these conditions have historically been grouped together and treated as the same disease.