mutations, notably the recurrent gain-of-function L265P variant, are a distinguishing feature of activated B-cell like (ABC) diffuse large B-cell lymphoma (DLBCL), leading to constitutive NFκB pathway activation. The aim of this study was to examine the distinct genomic profiles of -mutant DLBCL, notably according to the presence of the L265P or other non-L265P MYD88 variants. A cohort of 361 DLBCL cases (94 mutant and 267 wild-type) was submitted to next-generation sequencing (NGS) focusing on 34 genes to analyze associated mutations and copy number variations, as well as gene expression profiling, and clinical and prognostic analyses. Importantly, we highlighted different genomic profiles for MYD88 L265P and MYD88 non-L265P-mutant DLBCL, shedding light on their divergent backgrounds. Clustering analysis also segregated subgroups according to associated genetic alterations among patients with the same mutation. We showed that associated and MYD88 L265P mutations act synergistically to increase NFκB pathway activation, although the majority of MYD88 L265P-mutant cases harbors downstream NFκB alterations, which can predict BTK inhibitor resistance. Finally, although the MYD88 L265P variant was not an independent prognostic factor in ABC DLBCL, associated mutations significantly improved the survival of MYD88 L265P-mutant ABC DLBCL in our cohort. This study highlights the relative heterogeneity of -mutant DLBCL, adding to the field's knowledge of the theranostic importance of mutations, but also of associated alterations, emphasizing the usefulness of genomic profiling to best stratify patients for targeted therapy. .

From a liquid biopsy, cell-free DNA (cfDNA) can provide information regarding basal tumoral genetic patterns and changes upon treatment. In a prospective cohort of 30 diffuse large B-cell lymphomas (DLBCL), we determined the clinical relevance of cfDNA using targeted next-generation sequencing and its correlation with PET scan imaging at the time of diagnosis and during treatment. Using a dedicated DLBCL panel, mutations were identified at baseline for 19 cfDNAs and profiles were consistent with expected DLBCL patterns. Tumor burden-related clinical and PET scan features (LDH, IPI, and metabolic tumor volume) were significantly correlated with the quantity of tumoral cfDNA. Among the four patients presenting additional mutations in their cfDNAs, three had high metabolic tumor volumes, suggesting that cfDNA more accurately reflects tumor heterogeneity than tissues biopsy itself. Mid-treatment, four patients still had basal mutations in their cfDNAs, including three in partial response according to their Deauville scores. Our study highlights the major interests in liquid biopsy, in particular in the context of bulky tumors where cfDNA allows capturing the entire tumoral mutation profile. Therefore, cfDNA analysis in DLBCL represents a complementary approach to PET scan imaging.

Diffuse large B cell lymphoma (DLBCL) is an aggressive and heterogeneous malignancy that can be divided in two major subgroups, germinal center B-cell-like (GCB) and activated B-cell-like (ABC). Activating mutations of genes involved in the BCR and NF-κB pathways (CD79A, CD79B, MYD88, and CARD11) or in epigenetic regulation (EZH2) have been recently reported, preferentially in one of the two DLBCL subtypes. We analyzed the mutational status of these five recurrently mutated genes in a cohort of 161 untreated de novo DLBCL. Overall, 93 mutations were detected, in 61 (38%) of the patients. The L265P MYD88 mutation was the most frequent MYD88 variant (n = 18), observed exclusively in the ABC subtype. CD79A/CD79B ITAM domains were targeted in ABC DLBCL (12/77; 16%), whereas CARD11 mutations were equally distributed in the two subtypes. The EZH2 Y641 substitution was found almost exclusively in the GCB subgroup (15/62; 24%). Twenty cases (12%) displayed two activating mutations, including the most frequent CD79/MYD88 variants combination (n = 8) which is observed exclusively in the ABC subtype. When considering only ABC DLBCL patients treated by rituximab plus chemotherapy, the presence of an activating NF-κB mutation was associated with an unfavorable outcome (3-years OS 26% for mutated cases versus 67% for the cases without mutations, P = 0.0337). Our study demonstrates that activating and targetable mutations are observed at a very high frequency in DLBCL at the time of diagnosis, indicating that sequencing of a limited number of genes could help tailor an optimal treatment strategy in DLBCL.