ctDNA Is Useful to Detect Mutations at Codon 641 of Exon 16 of EZH2, a Biomarker for Relapse in Patients with Diffuse Large B-Cell Lymphoma

(1) Background: The epigenetic regulator EZH2 is a subunit of the polycomb repressive complex 2 (PRC2), and methylates H3K27, resulting in transcriptional silencing. It has a critical role in lymphocyte differentiation within the lymph node. Therefore, mutations at this level are implicated in lymphomagenesis. In fact, the mutation at the Y641 amino acid in the EZH2 gene is mutated in up to 40% of B-cell lymphomas. (2) Methods: We compared the presence of exon 16 EZH2 mutations in tumor samples and ctDNA in a prospective trial. These mutations were determined by Sanger sequencing and ddPCR. (3) 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 droplet digital PCR (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 Progression free survival (PFS) (95% interval confidence) was 27.7 (95% IC: 14-40) vs. 44.1 (95% IC: 40-47.6) months for the mutated vs. wild-type (wt) patients. (4) Conclusions: The ctDNA is useful for analyzing EZH2 mutations, which have an impact on PFS.