Balagué, Olga

Large B-cell lymphoma with IRF4 rearrangement (LBCL-IRF4) predominantly affects children and young adults (CAYA) and presents as localized disease with excellent prognosis. Although most tumors harbor IRF4 rearrangements (IRF4-R), the existence of cryptic rearrangements has been suggested. Whether IRF4-R LBCL in adults represents the same biological entity remains unclear. To address this question, 35 CAYA patients diagnosed with LBCL-IRF4 and 7 adult (>40-year-old) LBCL with IRF4-R were investigated by an integrative molecular approach. Targeted sequencing structural variant analysis (SV-NGS) confirmed the IRF4-R in 84% of investigated cases. In CAYA, an enrichment (55% vs 29% in adults) of translocations involving IGH, with a breakpoint cluster 3' to IRF4 (EXOC2) was observed, including a cryptic insertion of IGHM-IGHJ5 into IRF4 locus. Novel translocations, IRF4::MIR142 in two CAYA (7%) and IRF4::BATF in one adult, were discovered. Whole-exome sequencing analysis identified unreported mutations in LBCL-IRF4 as YY1 and ZC3H12A (11% each). The high incidence of mutations affecting the B-cell receptor/NF-KB pathways in LBCL-IRF4 was confirmed in cases with diffuse component only. None of the CAYA tumors were classified by LymphGen tool. Adult IRF4-R LBCL showed higher levels of genetic complexity and a distinct mutational profile with mutations on KMT2D and DTX1 (43% each), and MYD88-L265P (29%), and were predicted as EZB or MCD (29% each). These differential genetic features were in line with different clinical presentations (extranodal involvement and advanced stage). In conclusion, IRF4-R architecture and mutational profile differ according to age, supporting that not all cases should be classified as LBCL-IRF4.

Abstract Diffuse large B-cell lymphoma (DLBCL) with aberrant coexpression of CD10+BCL6+MUM1+ (DLBCL-AE), classified as germinal center B cell (GCB) type by the Hans algorithm (HA), was genetically characterized. To capture the complexity of DLBCL-AE, we used an integrated approach that included gene expression profiling (GEP), fluorescence in situ hybridization, targeted gene sequencing, and copy number (CN) arrays. According to GEP, 32/54 (59%) cases were classified as GCB-DLBCL, 16/54 (30%) as activated B-cell (ABC) DLBCL, and 6/54 (11%) as unclassifiable. The discrepancy between HA and GEP was 41%. Three genetic subgroups were identified. Group 1 included 13/50 (26%) cases without translocations and mainly showing and ABC/MCD molecular profile. Group 2 comprised 11/50 (22%) cases with IRF4 alterations (DLBCL-IRF4), frequent mutations in IRF4 (82%) and NF-κB pathway genes (MYD88, CARD11, and CD79B), and losses of 17p13.2. Five cases each were classified as GCB- or ABC-type. Group 3 included 26/50 (52%) cases with 1 or several translocations in BCL2/BCL6/MYC/IGH, and GCB/EZB molecular profile predominated. Two cases in this latter group showed complex BCL2/BCL6/IRF4 translocations. DLBCL-IRF4 in adults showed a similar copy number profile and shared recurrent CARD11 and CD79B mutations when compared with LBCL-IRF4 in the pediatric population. However, adult cases showed higher genetic complexity, higher mutational load with frequent MYD88 and KMT2D mutations, and more ABC GEP. IRF4 mutations were identified only in IRF4-rearranged cases, indicating its potential use in the diagnostic setting. In conclusion, DLBCL-AE is genetically heterogeneous and enriched in cases with IRF4 alterations. DLBCL-IRF4 in adults has many similarities to the pediatric counterpart.

Abstract Pediatric large B-cell lymphomas (LBCLs) share morphological and phenotypic features with adult types but have better prognosis. The higher frequency of some subtypes such as LBCL with IRF4 rearrangement (LBCL-IRF4) in children suggests that some age-related biological differences may exist. To characterize the genetic and molecular heterogeneity of these tumors, we studied 31 diffuse LBCLs (DLBCLs), not otherwise specified (NOS); 20 LBCL-IRF4 cases; and 12 cases of high-grade B-cell lymphoma (HGBCL), NOS in patients ≤25 years using an integrated approach, including targeted gene sequencing, copy-number arrays, and gene expression profiling. Each subgroup displayed different molecular profiles. LBCL-IRF4 had frequent mutations in IRF4 and NF-κB pathway genes (CARD11, CD79B, and MYD88), losses of 17p13 and gains of chromosome 7, 11q12.3-q25, whereas DLBCL, NOS was predominantly of germinal center B-cell (GCB) subtype and carried gene mutations similar to the adult counterpart (eg, SOCS1 and KMT2D), gains of 2p16/REL, and losses of 19p13/CD70. A subset of HGBCL, NOS displayed recurrent alterations of Burkitt lymphoma–related genes such as MYC, ID3, and DDX3X and homozygous deletions of 9p21/CDKN2A, whereas other cases were genetically closer to GCB DLBCL. Factors related to unfavorable outcome were age >18 years; activated B-cell (ABC) DLBCL profile, HGBCL, NOS, high genetic complexity, 1q21-q44 gains, 2p16/REL gains/amplifications, 19p13/CD70 homozygous deletions, and TP53 and MYC mutations. In conclusion, these findings further unravel the molecular heterogeneity of pediatric and young adult LBCL, improve the classification of this group of tumors, and provide new parameters for risk stratification.