IRF4-rearranged Large B-cell lymphoma (LBCL) has a genomic profile distinct to other LBCL in children and young adults

Pediatric large B-cell lymphomas (LBCL) 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 large B-cell lymphomas, not otherwise specified (DLBCL, NOS), 20 LBCL-IRF4, and 12 high grade B-cell lymphomas, NOS (HGBCL, NOS) in patients {less than or equal to}25 years-old 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-kB pathway genes (CARD11, CD79B and MYD88), losses of 17p13 and gains of chr7, 11q12.3-q25 whereas DLBCL,NOS were predominantly of germinal center B-cell (GCB) subtype and carried gene mutations similar to the adult counterpart (e.g. 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 >18y old, activated B-cell 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/young-adult LBCL, improve the classification of this group of tumors and provide new parameters for risk stratification.