Targeted next generation sequencing reveals high mutation frequency of CREBBP, BCL2 and KMT2D in high-grade B cell lymphoma with MYC and BCL2 and/or BCL6 rearrangements

Diffuse large B cell lymphoma (DLBCL) is the most common type of non-Hodgkin lymphoma. The update of the 4th edition of the 2017 WHO classification provides new concepts in the classification of DLBCL with the definition of 2 new categories : High-grade B cell lymphoma (HGBL) with MYC, BCL2 and/or BCL6 rearrangements so-called double-hit (DH) or triple-hit (TH) lymphomas, and HGBL, not otherwise specified (NOS) without MYC and BCL2 or BCL6 translocations [1] . Patients with MYC/BCL2 DHL, MYC/BCL6 DHL or MYC/BCL2/BCL6 THL will usually have an aggressive clinical course. We report here genomic characterization of 20 adult patients diagnosed with DHL harboring MYC and BCL2 (n = 15) or MYC and BCL6 (n = 2) rearrangements and 3 THL. To identify molecular variants, we performed targeted next generation sequencing (NGS) of FFPE samples of DHL/THL for mutations on 43 genes known to be important for lymphomagenesis. In all FFPE DHL/THL cases, our NGS Lymphopanel identified 438 alterations on 40 genes. Of these, 197/438 (45%) alterations localized on 33 genes are non-synonymous and predict amino-acid substitutions or truncation of the proteins. All samples harbor non-synonymous somatic alterations (5 to 18). The most frequently mutated genes are CREBBP (16/20 cases) followed by BCL2 (12/20), KMT2D (12/20), MYC (9/20), EZH2 (8/20), IGLL5 (8/20), FOXO1 (6/20) and SOCS1 (6/20). We also assessed the impact of AID involvement and found that IGLL5, SOCS1, MYC and BCL2 have the highest AID mutation frequency (40%, 38%, 30% and 27%, respectively) whereas KMT2D, FOXO1 and EZH2 show no AID induced mutations. Furthermore, DHL/THL mutations are mainly involved in apoptosis/cell-cycle (35% of total variants) and epigenetic regulation pathways (32% of total variants), known to be associated with a poor prognosis in lymphoma patients. In conclusion, our study describes for the first time the mutational landscape of DHL/THL, a poorly studied subtype of aggressive B cell lymphoma [2] .