Targeted EZH2 Inhibitors in Diffuse Large B-Cell Lymphoma (DLBCL): Immunohistochemical and Mutational Profiles of Patients May Determine Candidates for Treatment

• Published in: Blood 2014-12, Vol.124 (21), p.1656-1656
• Main Authors: Dubois, Sydney, Mareschal, Sylvain, Cornic, Marie, Picquenot, Jean-Michel, Bertrand, Philippe, Bohers, Elodie, Maingonnat, Catherine, Viailly, Pierre-Julien, Ruminy, Philippe, Alcantara, Marion, Bastard, Christian, Jardin, Fabrice, Tilly, Herve
• Format: Article
• Language: English
• ISSN: 0006-4971; 1528-0020
• DOI: 10.1182/blood.V124.21.1656.1656

▪ DLBCL is the most common lymphoid malignancy, accounting for 30-40% of all Non Hodgkin Lymphomas. Gene expression profiling has identified two main subtypes: Germinal Center B-Cell like (GCB) and Activated B-Cell like (ABC). EZH2 plays an essential role in epigenetic regulation of DLBCL by specifically mono-, bi- and tri-methylating histone H3 lysine 27 (H3K27me1/-me2/-me3). Recurrent somatic heterozygous gain-of-function mutations of EZH2 have been identified in DLBCL, mostly affecting tyrosine 641 (Y641), inducing increased H3K27me3. Novel EZH2 inhibitors are currently being tested in phase 1 and 2 clinical trials in patients with and without EZH2 Y641 mutations, but no study has examined which patients would most benefit from this treatment. We studied a cohort of 100 patients with DLBCL with available biopsies (96 at diagnosis and 4 at relapse) and developed an immunohistochemical (IHC) assay based on antibodies specifically targeting EZH2, H3K27me3 or H3K27me2. Eighty-six biopsies (12 EZH2 Y641 mutant and 74 WT EZH2) were usable for IHC analysis. Biopsies were scored based on staining intensity and percentage of tumor cells stained, and a me3/me2 score (log of me3 to me2 ratio) was calculated for each patient. Sanger sequencing of EZH2was performed on all patients, GCB/ABC signature was determined by DASL technology based on the expression of 19 genes, and t(14;18) translocation was detected by karyotyping and FISH. The cohort was also extended to 15 patients with EZH2 Y641 mutations and 17 WT EZH2 patients for Next Generation Sequencing (NGS) analysis of a panel of 34 genes involved in lymphomagenesis. Among our cohort, 45 patients were ABC, 50 were GCB, and 5 were unclassified. Sanger sequencing identified 14 patients with EZH2 Y641 mutations (12 GCB, 1 ABC, 1 unclassified). The t(14;18) translocation was more frequent in patients with EZH2 Y641 mutations (9/14, 64%) (p0, n=12/86), a me3-low/me2-high profile (me3/me2 score0 profiles (n=7/12), whereas patients with WT EZH2 are split between intermediate (n=29/74) and me3/me2 score