Detection of 2-Hydroxyglutarate by 3.0-Tesla Magnetic Resonance Spectroscopy in Gliomas with Rare IDH Mutations: Making Sense of "False-Positive" Cases

Reliable detection of genetic alterations in cyst fluid DNA for the diagnosis of brain tumors

PURPOSE

Liquid biopsy of cyst fluid in brain tumors has not been extensively studied to date. The present study was performed to see whether diagnostic genetic alterations found in brain tumor tissue DNA could also be detected in cell-free DNA (cfDNA) of cyst fluid in cystic brain tumors.

METHODS

Cyst fluid was obtained from 22 patients undergoing surgery for a cystic brain tumor with confirmed genetic alterations in tumor DNA. Pathological diagnoses based on WHO 2021 classification and diagnostic alterations in the tumor DNA, such as IDH1 R132H and TERT promoter mutation for oligodendrogliomas, were detected by Sanger sequencing. The same alterations were analyzed by both droplet digital PCR (ddPCR) and Sanger sequencing in cyst fluid cfDNA. Additionally, multiplex ligation-dependent probe amplification (MLPA) assays were performed to assess 1p/19q status, presence of CDKN2A loss, PTEN loss and EGFR amplification, to assess whether differentiating between astrocytomas and oligodendrogliomas and grading is possible from cyst fluid cfDNA.

RESULTS

Twenty-five genetic alterations were found in 22 tumor samples. All (100%) alterations were detected in cyst fluid cfDNA by ddPCR. Twenty of the 25 (80%) alterations were also detected by Sanger sequencing of cyst fluid cfDNA. Variant allele frequency (VAF) in cyst fluid cfDNA was comparable to that of tumor DNA (R = 0.62, Pearson's correlation). MLPA was feasible in 11 out of 17 (65%) diffuse gliomas, with close correlation of results between tumor DNA and cyst fluid cfDNA.

CONCLUSION

Cell-free DNA obtained from cyst fluid in cystic brain tumors is a reliable alternative to tumor DNA when diagnosing brain tumors.

Advances in molecular and imaging biomarkers in lower-grade gliomas

INTRODUCTION

Lower-grade (grade 2-3) gliomas (LGGs) constitutes a group of primary brain tumors with variable clinical behaviors and treatment responses. Recent advancements in molecular biology have redefined their classification, and novel imaging modalities emerged for the noninvasive diagnosis and follow-up.

AREAS COVERED

This review comprehensively analyses the current knowledge on molecular and imaging biomarkers in LGGs. Key molecular alterations, such as IDH mutations and 1p/19q codeletion, are discussed for their prognostic and predictive implications in guiding treatment decisions. Moreover, the authors explore theranostic biomarkers for the potential of tailored therapies. Additionally, they also describe the utility of advanced imaging modalities, including widely available techniques, as dynamic susceptibility contrast perfusion-weighted imaging and less validated, emerging approaches, for the noninvasive LGGs characterization and follow-up.

EXPERT OPINION

The integration of molecular markers enhanced the stratification of LGGs, leading to the new concept of integrated histomolecular classification. While the IDH mutation is an established key prognostic and predictive marker, recent results from IDH inhibitors trials showed its potential value as a theranostic marker. In this setting, advanced MRI techniques such as 2-D-hydroxyglutarate spectroscopy are very promising for the noninvasive diagnosis and monitoring of LGGs. This progress offers exciting prospects for personalized medicine and improved treatment outcomes in LGGs.

Exceptionally rare IDH1-mutant adult medulloblastoma with concurrent GNAS mutation revealed by in vivo magnetic resonance spectroscopy and deep sequencing

Medulloblastoma (MB) is the most common malignant brain tumor occurring in childhood and rarely found in adults. Based on transcriptome profile, MB are currently classified into four major molecular groups reflecting a considerable biological heterogeneity: WNT-activated, SHH-activated, group 3 and group 4. Recently, DNA methylation profiling allowed the identification of additional subgroups within the four major molecular groups associated with different clinic-pathological and molecular features. Isocitrate dehydrogenase-1 and 2 (IDH1 and IDH2) mutations have been described in several tumors, including gliomas, while in MB are rarely reported and not routinely investigated. By means of magnetic resonance spectroscopy (MRS), we unequivocally assessed the presence the oncometabolite D-2-hydroxyglutarate (2HG), a marker of IDH1 and IDH2 mutations, in a case of adult MB. Immunophenotypical work-up and methylation profiling assigned the diagnosis of MB, subclass SHH-A, and molecular testing revealed the presence of the non-canonical somatic IDH1(p.R132C) mutation and an additional GNAS mutation, also rarely described in MB. To the best of our knowledge, this is the first reported case of MB simultaneously harboring both mutations. Of note, tumor exhibited a heterogeneous phenotype with a tumor component displaying glial differentiation, with robust GFAP expression, and a component with conventional MB features and selective presence of GNAS mutation, suggesting co-existence of two different major tumor subclones. These findings drew attention to the need for a deeper genetic characterization of MB, in order to get insights into their biology and improve stratification and clinical management of the patients. Moreover, our results underlined the importance of performing MRS for the identification of IDH mutations in non-glial tumors. The use of throughput molecular profiling analysis and advanced medical imaging will certainly increase the frequency with which tumor entities with rare molecular alterations will be identified. Whether these findings have any specific therapeutic implications or prognostic relevance requires further investigations.