The initial discovery of molecular heterogeneity arose from gene expression profiling (GEP) and showed that DLBCL can be divided into cell of origin subgroups, with expression profiles resembling normal germinal-center B-cells and in vitro-activated B-cells, defined as GCB- and ABC-DLBCL, respectively. The gene discussed is ABCB6; the disease is diffuse large B-cell lymphoma.