Gene Expression Profiling of Diffuse Large B-Cell Lymphomas Supervised by CD5 Expression

Abstract 4164

Diffuse large B-cell lymphoma (DLBCL) is the most common non-Hodgkin lymphoma and is composed of heterogeneous groups of lymphoma with pathophysiological, genetic and clinical features. Gene expression profiling identified two distinct forms of DLBCL: activated B cell-like (ABC) and germinal center B-cell-like (GCB) types. ABC DLBCL shows more activated phenotype characterized with high activity of the NF-kappa B pathway and worse prognosis than GCB DLBCL. CD5-positive (CD5+) DLBCL comprises 5 to 10% of DLBCL and is one of the immunohistochemical subgroups in the 2008 WHO classification. It shows many distinct clinical characteristics with elderly onset, advanced stage at diagnosis, high serum lactate dehydrogenase level and frequent involvement of extranodal sites. Despite the use of rituximab, CD5+ DLBCL shows a poor prognosis and high incidence of central nervous system (CNS) relapse. More than 80% of patients with CD5+ DLBCL are classified as non-GCB subgroup by Hans' method; however, few molecular studies have been reported. To clarify the difference between CD5+ DLBCL and CD5-negative (CD5-) DLBCL in the gene expression profile, total RNA from 90 patients with de novo DLBCL including 33 CD5+ DLBCLs and 57 CD5- DLBCLs was examined using Agilent 44K human oligo-microarrays (Agilent 4112F). The expression of CD5 in tumor cells was confirmed by means of immunohistochemistry using frozen sections. Cases of primary mediastinal large B-cell lymphoma, intravascular large B-cell lymphoma and primary DLBCL of the CNS were excluded from the present study. Supervised hierarchical clustering of the expression data could separate the DLBCL cases into the two groups, CD5+ DLBCL and CD5- DLBCL. A signature gene set supervised by CD5 expression included some of the same genes (SH3BP5, CCND2, LMO2) in the predictor gene set to discriminate between GCB and ABC DLBCLs. To classify the difference between CD5+ ABC DLBCL and CD5- ABC DLBCL in the gene expression profile, the 90 DLBCLs were analyzed by the Rosenwald's gene set (NEJM, 2002). Those cases were separated with 78 ABC DLBCLs and 12 GCB DLBCLs. Incidence of CD5+ cases was 42% (33/78) in ABC DLBCLs and 0% in GCB DLBCLs. A classifier based on gene expression at supervised analysis also correctly identified CD5 expression in ABC DLBCL. Signature genes to distinguish between CD5+ ABC DLBCL and CD5- ABC DLBCL were as follows: SNAP25, SYCP3, CCNA1, MAPK4, CCNA1, LMO3, NLGN3, GRIN2A, AQP4, FGFR2, NEUROD1, KL, FGF1, SYT5, etc., were overexpressed in CD5+ ABC DLBCL, and CYP4Z1, MDM2, IL7R, GRLF1, TNFRSF9, CD1A etc., were overexpressed in CD5- ABC DLBCL. Enriched Gene Ontology (GO) categories in CD5+ ABC DLBCL were synapse, multicellular organismal process, fibroblast growth factor receptor signaling pathway, cell projection, alcohol dehydrogenase activity and glucuronosyltransferase activity. Among them, synapse was the top GO category (P=6.1E-05). In conclusion, our current study confirmed that most of CD5+ DLBCLs are classified as ABC DLBCL by gene expression profiling. Our results suggest that neurological component- and function-related genes in the CD5+ ABC DLBCL signature gene set may be related to the high frequency of CNS relapse in CD5+ DLBCL.