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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.

TO THE EDITOR: Follicular lymphoma (FL) is characterized by the t(14;18)(q32;q21) chromosomal translocation,[1][1] found in ∼85% of manifest FL (mFL) cases. The t(14;18) is also present in early precursor lesions of FL and in a significant fraction of healthy individuals.[2][2],[3][3] This

Pediatric-type follicular lymphoma (PTFL) is a B-cell lymphoma with distinctive clinicopathological features. Recently, recurrent genetic alterations of potential importance for its pathogenesis that disrupt pathways associated with the germinal center reaction (TNFRSF14, IRF8), immune escape (TNFRSF14), and anti-apoptosis (MAP2K1) have been described. In an attempt to shed more light onto the pathogenesis of PTFL, an integrative analysis of these mutations was undertaken in a large cohort of 43 cases previously characterized by targeted next-generation sequencing and copy number array. Mutations in MAP2K1 were found in 49% (20/41) of the cases, second in frequency to TNFRSF14 alterations (22/41; 54%), and all together were present in 81% of the cases. Immunohistochemical analysis of the MAP2K1 downstream target extracellular signal-regulated kinase demonstrated its phosphorylation in the evaluable cases and revealed a good correlation with the allelic frequency of the MAP2K1 mutation. The IRF8 p.K66R mutation was present in 15% (6/39) of the cases and was concomitant with TNFRSF14 mutations in 4 cases. This hot spot seems to be highly characteristic for PTFL. In conclusion, TNFRSF14 and MAP2K1 mutations are the most frequent genetic alterations found in PTFL and occur independently in most cases, suggesting that both mutations might play an important role in PTFL lymphomagenesis.

Pediatric-type follicular lymphoma (PTFL) is a variant of follicular lymphoma (FL) with distinctive clinicopathological features. Patients are predominantly young males presenting with localized lymphadenopathy; the tumor shows high-grade cytology and lacks both BCL2 expression and t(14; 18) translocation. The genetic alterations involved in the pathogenesis of PTFL are unknown. Therefore, 42 PTFL (40 males and 2 females; mean age, 16 years; range, 5-31) were genetically characterized. For comparison, 11 cases of conventional t(14: 18)(-) FL in adults were investigated. Morphologically, PTFL cases had follicular growth pattern without diffuse areas and characteristic immunophenotype. All cases showed monoclonal immunoglobulin (IG) rearrangement. PTFL displays low genomic complexity when compared with t(14; 18)(-) FL (mean, 0.77 vs 9 copy number alterations per case; P

Pediatric-type follicular lymphoma (PTFL) is a B-cell lymphoma with distinctive clinicopathological features. Recently, recurrent genetic alterations of potential importance for its pathogenesis that disrupt pathways associated with the germinal center reaction (

BACKGROUND Pediatric aggressive large B-cell lymphomas (LBCL) share morphological and phenotypic features with adult types but seem to have better prognosis. Additionally, a specific subtype carrying IRF4 translocations (LBCL-IRF4) has been recently identified in this age group. In adults, the cell-of-origin (COO) distinction of diffuse large B-cell lymphoma (DLBCL) based on gene expression signatures (germinal center B-cell like, GCB and activated B-cell like, ABC) and more recently clusters of genetic alterations have identified molecularly distinct DLBCL subsets that may benefit from novel therapeutic targets. The integration of pediatric population in these clinically relevant molecular subgroups and its clinical importance is not well known. The aim of this study was to characterize the molecular heterogeneity of LBCL in pediatric and young adult patients and evaluate their potential clinical impact. DESIGN Sixty-one LBCL diagnosed in patients ≤25 years-old (median age 14 years old, male/female 38/23) were included in the study. Molecular analyses included fluorescence in situ hybridization for MYC, BCL2, IRF4 and BCL6, copy number (CN) analysis (Oncoscan, Affymetrix), COO Lymph2Cx assay (NanoString) and targeted next generation sequencing of 96 B-cell lymphoma driver genes (SureSelect XT, Agilent Technologies). CNA and mutational profiles were compared to those previously published in adult DLBCL. Correlation of molecular features and event free survival (EFS) was performed using Kaplan-Meier curves. RESULTS Histologically, 33 were DLBCL, 20 LBCL-IRF4 and 8 high grade B-cell lymphomas, not otherwise specified (HGBCL). Nodal disease was present in 57%, mainly in the cervical region. COO distribution was: 68% GCB, 18% ABC and 13% unclassified. Most of LBCL-IRF4 cases were GCB-COO (73%). The IRF4 translocation was demonstrated in 16 out of 19 cases diagnosed as LBCL-IRF4 and an IGH rearrangement was seen in the other 3. Five cases carried MYC-breaks (3 DLBCL and 2 HGBCL) and two cases carried BCL6-breaks (1DLBCL and 1HGBCL). BCL2 rearrangements were absent. CN analysis detected alterations in 46/51 cases with recurrent gains (>15%) of 1q, 2p16, 11q, trisomies 7 and 12, and recurrent losses (>10%) of 1p36, 6q21-q22, 15q24, 17p13 and 19p13. Recurrent homozygous deletions were observed at 19p13/CD70 (6 cases), 9p13/CDKN2A (3 cases) and 13q14/RB1 (2 cases). Alteration patterns suggestive of chromothripsis were found in 10% (5/51) of the cases. No ABC-DLBCL related alterations such as 3p21-p14, 6q21-q25, 9p21.3 and 17p13 losses were seen. Targeted sequencing detected a total of 434 variants in 44 of 47 cases (mean 9.2 mutations/case). A pipeline for selection of driver mutations revealed a total of 270 mutations (62%) with potential functional effect. Recurrent mutations found in >15% of the cases affected IRF4, SOCS1, PIM1, CARD11, ACTB and CCND3 genes. In comparison to adult DLBCL, pediatric and young adult cases had significantly lower incidence of MYD88 (5 cases), CREBBP,TP53 (3 cases each) and TNFRSF14 (2 cases) mutations which are strongly associated with the definition of established mutational clusters in adult DLBCL. In our cohort, the morphological subtypes displayed different molecular profiles. IRF4 variants (some cases with >7 variants) and mutations in NF-kB pathway (CARD11, CD79B and MYD88-non L265P) were found specifically in the LBCL-IRF4 subgroup, whereas mutations in GCB related genes such as SOCS1 and EZH2 were particularly seen in cases with DLBCL diagnosis. All 49 patients with available follow-up received chemotherapy as first line treatment (41% containing Rituximab). Variables significantly associated with poor EFS in univariate analysis were age >18 years, ABC-COO, Stage IV, high genetic complexity (chromothripsis and/or >10 CN alterations), 2p16/REL gain/amplification, 9p21.3/CDKN2A homozygous deletions, MYC rearrangements and mutations in MYC, TP53 and DDX3X genes. CONCLUSION Despite pediatric/young-adult LBCL having overlapping features with adult disease our findings suggest that LBCL in young age have specific molecular mechanisms and highlight potential key drivers of these lymphomas in this age group. Disclosures No relevant conflicts of interest to declare.