Parallel testing of liquid biopsy (ctDNA) and tissue biopsy samples reveals a higher frequency of EZH2 mutations in follicular lymphoma

Abstract

BackgroundRecent genomic studies revealed enhancer of zeste homolog 2 (EZH2) gain‐of‐function mutations, representing novel therapeutic targets in follicular lymphoma (FL) in around one quarter of patients. However, these analyses relied on single‐site tissue biopsies and did not investigate the spatial heterogeneity and temporal dynamics of these alterations.ObjectivesWe aimed to perform a systematic analysis of EZH2 mutations using paired tissue (tumor biopsies [TB]) and liquid biopsies (LB) collected prior to treatment within the framework of a nationwide multicentric study.MethodsPretreatment LB and TB samples were collected from 123 patients. Among these, 114 had paired TB and LB, with 39 patients characterized with paired diagnostic and relapse samples available. The EZH2 mutation status and allele burden were assessed using an in‐house‐designed, highly sensitive multiplex droplet digital PCR assay.ResultsEZH2 mutation frequency was found to be 41.5% in the entire cohort. In patients with paired TB and LB samples, EZH2 mutations were identified in 37.8% of the patients with mutations exclusively found in 5.3% and 7.9% of TB and LB samples, respectively. EZH2 mutation status switch was documented in 35.9% of the patients with paired diagnostic and relapse samples. We also found that EZH2 wild‐type clones may infiltrate the bone marrow more frequently compared to the EZH2 mutant ones.ConclusionThe in‐depth spatio‐temporal analysis identified EZH2 mutations in a considerably higher proportion of patients than previously reported. This expands the subset of FL patients who most likely would benefit from EZH2 inhibitor therapy.

EZH2 mutations in follicular lymphoma distort H3K27me3 profiles and alter transcriptional responses to PRC2 inhibition

“…Indeed, we speculate that the abundance of EZH2 -WT FL subclones may be predictive of a shorter time to relapse after PRC2 inhibitor treatment. It will therefore be very informative to evaluate not only the presence of EZH2 mutations but also their VAF, to search for EZH2 mutations in liquid biopsies (circulating DNA) 72 or to analyze EZH2 mutations from more than one biopsy. Furthermore, EZH2 mutation status has recently been suggested to potentially predict response to treatments other than PRC2 inhibitors 73 .…”