Molecular determinants of clinical outcomes in a real-world diffuse large B-cell lymphoma population

•DHITsig expression extends beyond HGBCL-DH-BCL2 to identify dark zone lymphomas and was thus renamed the “DZsig.”•DZsig refines cell-of-origin classification by identifying patients within GCB-DLBCL with inferior outcomes and shorter time to treatment. [Display omitted] Molecular heterogeneity of diffuse large B-cell lymphoma (DLBCL) underlies the variable outcomes achieved with immunochemotherapy. However, outcomes of gene expression profiling (GEP)–defined molecular subgroups in a real-world DLBCL population remain unknown. Here we examined the prevalence and outcomes of molecular subgroups in an unselected population of 1149 patients with de novo DLBCL in British Columbia, Canada. Evaluable biopsies were profiled by fluorescence in situ hybridization (FISH), immunohistochemistry, and digital GEP to assign cell-of-origin and the so-called “double-hit signature” (DHITsig)—a signature originally described as being characteristic for high-grade B-cell lymphoma with MYC and BCL2 rearrangements (HGBCL-DH-BCL2). DHITsig was expressed in 21% of 431 germinal center B-cell-like (GCB)–DLBCL and all 55 Burkitt lymphomas examined. Reflecting this latter finding, DHITsig has been renamed the “dark zone signature” (DZsig). DZsigpos-DLBCL, non-DZsigpos GCB-DLBCL and activated B-cell-like (ABC)–DLBCL were associated with a 2 year overall survival of 57%, 89%, and 71%, respectively. 62% of DZsigpos tumors were negative for HGBCL-DH-BCL2 by FISH, but were associated with outcomes similar to HGBCL-DH-BCL2. A small group of HGBCL-DH-BCL2 that lacked DZsig expression had different molecular features compared with DZsig-expressing HGBCL-DH-BCL2 and were associated with favorable outcomes comparable to DLBCL, not otherwise specified. DZsigpos and ABC-DLBCL had a shorter diagnosis-to-treatment interval (DTI) than GCB-DLBCL, with this metric being associated with outcome. In conclusion, DZsig expression extends beyond HGBCL-DH-BCL2 and captures a poor-prognosis DLBCL subgroup with short DTI, including patients unidentifiable by routine FISH testing, that should be considered for treatment intensification or novel therapies in prospective trials. Aggressive B-cell lymphomas are both molecularly and clinically heterogeneous, creating challenges for systems that attempt to classify them into clinically relevant entities. Alduaij et al advance the field by reporting on the utility of a dark zone signature (DZsig), originally identified in double-hit lymphoma in the diagnosis of agg