Abstract 4020: Methylation analysis of matched primary and recurrent IDH-mutant astrocytoma; an update from the GLASS-NL consortium
Authors: Vallentgoed Wies Rijan , Niers Anneke , van Garderen Karin , Bent Martin van den , van Dijk Erik , Draaisma Kaspar , van Eijk Paul , de Heer Iris , Kouwenhoven Mathilde , Kros Johan , de Leng Wendy , Martin Ivonne , Robe Pierre , Smits Marion , Tesileanu Mircea , van Thuijl Hinke , Verhaak Roel , Westerman Bart , Wiel Mark van de , Ylstra Bauke , Wesseling Pieter , French Pim 
Published: June 2022

Abstract
INTRODUCTION. Diffuse gliomas are the most frequent and devastating primary CNS tumors in adults. Standard treatment has limited efficacy and without exception these gliomas recur. The evolutionary processes that drive progression in glioma of the IDH-mutant astrocytoma subgroup, remain unclear. The GLASS-NL consortium was initiated to gain insight into the molecular mechanisms underlying glioma evolution and to identify markers of progression in IDH-mutant astrocytomas. Such markers can ultimately assist clinical decision making. Here, we present the results of genome wide DNA-methylation profiling of samples included in the GLASS-NL study.
METHODS. 110 adult patients were identified with an IDH-mutant, 1p19q non-codeleted, astrocytoma at first diagnosis. All patients underwent surgical resection of the tumor at least twice, separated by &gt;6 months with a median of 41.9 months (IQR:26.5-65.9). After surgical resection of the initial tumor, 63% and 22% of the patients were treated with radiotherapy or chemotherapy respectively. DNA-methylation profiling was performed on 235 samples from 103 patients, using the Illumina Infinium MethylationEPIC BeadChip array. Copy number alterations (CNAs) were extracted from these data. Methylation subclasses were determined according to Capper et al. (Nature, 2018). Overall survival (OS) was measured from date of initial surgery.
RESULTS. Of all primary tumors, 85 (87%) of the tumor samples were assigned to the A_IDH (‘low grade’) methylation subclass and 10 (10%) to the A_IDH_HG (‘high grade’) subclass. The relative proportion of high grade tumors increased ~three-fold at tumor recurrence (32/101, 32%) and even further in the second recurrence (15/29, 52%). The high grade subclass of the recurrent, but not the initial tumor sample, was negatively associated with OS (p &lt; 0.0001). The overall DNA-methylation levels of recurrent samples were lower than that of initial samples. This difference is explained by the increased number of high grade samples at recurrence, since near identical DNA-methylation levels were observed in samples that remained low grade. Analysis of CNAs revealed several chromosomal arms and bands that were more frequently altered in samples of the high grade methylation subclass compared to low grade. In addition, gains and losses of specific genes, such as homozygous deletion (HD) of CDKN2A/B, were more frequent in high grade samples. Overall DNA-methylation levels of recurrent samples with CDKN2A/B HD were lower than that of samples without this deletion. However, CDKN2A/B HD alone does not fully explain DNA-demethylation at malignant progression and other molecular aberrations are likely to contribute as well.
CONCLUSION. Longitudinal methylation profiling analysis of IDH-mutant astrocytoma reveals a shift towards a higher grade at tumor recurrence coinciding with reduced genome-wide DNA-methylation levels.

Citation Format: Wies Rijan Vallentgoed, Anneke Niers, Karin van Garderen, Martin van den Bent, Erik van Dijk, Kaspar Draaisma, Paul van Eijk, Iris de Heer, Mathilde Kouwenhoven, Johan Kros, Wendy de Leng, Ivonne Martin, Pierre Robe, Marion Smits, Mircea Tesileanu, Hinke van Thuijl, Roel Verhaak, Bart Westerman, Mark van de Wiel, Bauke Ylstra, Pieter Wesseling, Pim French. Methylation analysis of matched primary and recurrent IDH-mutant astrocytoma; an update from the GLASS-NL consortium [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 4020.