Clonal relationship and mutational landscape of diffuse large B-cell lymphoma recurrences
Patients with diffuse large B-cell lymphoma (DLBCL) still develop a relapse in 30-40% of the cases after first-line treatment, where some patients even present with multiple recurrences. Often, the clonal relationship between the initial diagnosis and subsequent lymphomas is not routinely assessed, where the occurrence of clonally unrelated lymphoma remains unknown. In addition, the molecular mechanisms underlying relapse development and failure of treatment in DLBCL are still poorly understood. To determine the prevalence of second primary lymphoma in patients with relapsed DLBCL and identify relapse-associated driver genes, we aim to investigate the clonal relationship and mutational landscape of DLBCL recurrences.
The study cohort consisted of 39 paired DLBCL diagnosis-relapse(s) samples. Clonality assessment was performed by next-generation sequencing (NGS) of immunoglobulin (IG) gene rearrangements, as developed by the EuroClonality-NGS working group1. The clonotypes for the different IG gene rearrangements were identified by ARReST/Interrogate bioinformatics. Mutation analysis was carried out by whole-exome sequencing (WES) on a subset of paired diagnosis-relapse(s) samples.
IG-NGS clonality analyses on matched diagnosis-relapse(s) samples revealed identical dominant clonotype(s) in 90% (35/39) of the recurrences, even in cases with an interval period of 14 years between the primary diagnosis and relapse. However, in 10% (4/39) of the DLBCL patients, at least one of the recurrences was clonally unrelated, which in all cases involved relapses that occurred after 5 years. WES data analysis of the first six paired diagnosis-relapse samples showed a range of 58-229 single nucleotide variants (SNVs) that were shared between diagnosis and relapse, while 1-18 variants were enriched in the relapsed samples, exhibiting significant higher variant allele frequencies (VAF) compared to matched diagnosis sample. These included mutations in TP53, CD58 and TBL1XR1. Moreover, multiple relapse-specific SNVs were detected, including mutations affecting MYD88 and BTG1. Currently, additional cases are subjected to WES in order to identify common relapse-associated mutations and define patterns of clonal evolution.
DLBCL recurrences represent clonally unrelated lymphomas in ~10% of the cases, suggesting the occurrence of second primary lymphoma, possibly linked to a genetic predisposition or immunodeficiency. Genome-wide mutational analyses of clonally related cases will define the patterns of clonal evolution in relapsed DLBCL and identify genes related to therapy resistance, unravelling the genetic landscape of relapsed DLBCL.
1 Scheijen B et al. Next-generation sequencing of immunoglobulin gene rearrangements for clonality assessment: a technical feasibility study by EuroClonality-NGS. Leukemia 2019; 33: 2227-2240.