IBCL-057: Liquid Biopsy-Based Monitoring of Ezh2 Mutations in Follicular Lymphoma: Implications for Non-Invasive Disease Monitoring and Targeted Therapy

Abstract

Context: Follicular lymphoma (FL) is the most common type of indolent non-Hodgkin lymphomas, with an average overall survival rate of 15 years. The majority of FL patients experience disease progression or high-grade transformation to a more aggressive lymphoma, raising the need for effective treatment response monitoring, which, however, is hampered by the limited specificity and sensitivity of the most widely used, imaging-based PET-CT method. Molecular analysis of tumor-derived circulating DNA (ctDNA), frequently referred as liquid biopsy, is a promising, minimally invasive, radiation-free disease monitoring tool for patients suffering from a wide range of different tumor types. Recent studies interrogating the genomic background of FL have revealed activating mutations in the epigenetic regulator EZH2 gene in 25% of patients at diagnosis. Objective: In this feasibility study, we tested the power of detection and time-resolved monitoring of EZH2 mutations in ctDNA of FL patients receiving immunochemotherapy (ICT). Methods: Thirty-five blood plasma samples have been collected from 19 EZH2 mutant FL patients treated with ICT. After ctDNA isolation, EZH2 mutations were screened in each sample using digital droplet PCR (Bio-Rad Laboratories, USA). The acquired genetic results were compared with PET-CT-based imaging data where available. Results: EZH2 mutations were detected in plasma samples of four patients suffering from active or transformed FL. All patients with EZH2 wild type plasma samples were in complete or partial remission. In patients with EZH2 mutation-positive ctDNA, allele frequencies of the mutations correlated with the amount of metabolically active tumor sites observed on PET-CT scan images. Variant allele frequencies of EZH2 mutations rapidly declined or dropped below the detection limit upon successful treatment, while in one patient, treatment failure was associated with high EZH2 variant allele frequency. We also demonstrated spatial heterogeneity of EZH2 mutations in another case where different EZH2 mutations deriving from distinct anatomical sites could simultaneously be detected in the plasma. Conclusions: Our results suggest that liquid biopsy-based EZH2 mutation analysis with sensitive digital droplet PCR method offers a real-time, radiation-free, sensitive treatment response monitoring tool for patients with active EZH2 mutant FL.