Mutations at Codon 641 of Exon 16 of EZH2 in Circulating Tumor DNA: A Biomarker for Relapse in Patients With Diffuse Large B-cell Lymphoma Treated With the R-CHOP Scheme.

Abstract Background: The epigenetic regulator EZH2 is a subunit of the polycomb repressive complex 2 (PRC2), methylates H3K27, resulting in transcriptional silencing. The mutation at Y646 amino acid in the EZH2 gene is mutated in up to 40 % of B-cell lymphomas. Methods: We compared the presence of exon 16 EZH2 mutations in tumor samples and ctDNA in a prospective trial. The mutations were determined by sanger sequencing, and by ddPCR. We also evaluated the impact of these mutations on response, relapse, and survival. Results: One hundred and thirty-eight cases were included. Ninety-eight were germinal center, and twenty had EZH2 mutations. Mean follow-up (IQR 25-75) was 23 (7- 42) months. The tumor samples were considered the standard of reference. Considering the results of the mutation in ctDNA by Sanger sequencing, the sensibility (Se) and specificity (Sp) were 52 % and 99 %, respectively. After adding the ddPCR analysis, the Se and Sp increased to 95 and 100 %, respectively. After bivariate analysis, only the presence of double-hit lymphoma (p=0.04), or EZH2 mutations were associated with relapse. The median PFS (95 % Interval confidence) was 27.7 (95 % IC: 14-40) vs 44.1 (95 % IC: 40-47.6) months for the mutated vs wt patients. Conclusions: The ctDNA is usefull to analyse EZH2 mutations, which have an impact in PFS.