1 Laura Kiss
2 Ákos Nagy MD
3 Csaba Bödör PhD DSc
1,2,3 HCEMM-SU Molecular Oncohematology Research Group, Department of Pathology and Experimental Cancer Research, Semmelweis University, Budapest
Follicular lymphoma (FL) is the most common indolent non-Hodgkin's lymphoma. The disease has favourable outcome however relapses and high-grade transformation may occur. Investigating the molecular background of FL revealed that mutations of the EZH2 epigenetic regulatory gene are present in 25% of the cases. Further evaluation of these mutations has clinical and therapeutic relevance due to their gain-of-function nature, making this molecular aberration the first precision oncological target in FL. The heterogeneous disease course raises the need for an effective disease monitoring system. An emerging option is liquid-biopsy (LB) that is a minimally invasive method based on circulating cell-free DNA (cfDNA) analysis. It offers a real-time disease monitoring alternative as well as enabling the assessment of spatial heterogeneity by simultaneously representing molecular alterations in different lymph node areas.
In parallel to studying spatial heterogeneity we also aimed to compare the quantitative indicators of the liquid-biopsy test with the currently standard single-site tissue biopsies (TB). In addition, the study focuses on the correlation between EZH2 variant allele frequency (VAF), EZH2 mutation status and clinical/histological indicators (grade, stage, bone marrow infiltration).
Pretreatment paired LB and TB samples were collected from 117 patients. To characterize the EZH2 mutation status, samples were tested by droplet digital PCR method (Bio-Rad, USA) in a self-enhanced multiplex PCR setup.
By testing paired TB and LB samples the mutation frequency proved to be 38%. The proportion of cases that harbored a mutation by only one of these techniques was 5% and 7% for TB and LB, respectively. Higher histological grade was significantly associated with mutant EZH2 status and higher VAF. In addition, B symptoms were reported more commonly in EZH2 mutant cases. We also identified that EZH2 wild-type clones infiltrated the bone marrow more frequently than mutant ones.
Our results suggest that parallel testing of TB and LB samples yields a higher EZH2 mutation frequency in FL, thereby expanding the group of patients who may be eligible for the EZH2 inhibitor therapy.
Semmelweis University, firstname.lastname@example.org, Csaba Bödör Phd DSc, Ákos Nagy MD