Impact of Rare and Multiple Concurrent Gene Fusions on Diagnostic DNA Methylation Classifier in Brain Tumors

DNA methylation is an essential molecular assay for central nervous system (CNS) tumor diagnostics. While some fusions define specific brain tumors, others occur across many different diagnoses. We performed a retrospective analysis of 219 primary CNS tumors with whole genome DNA methylation and RNA next-generation sequencing. DNA methylation profiling results were compared with RNAseq detected gene fusions. We detected 105 rare fusions involving 31 driver genes, including 23 fusions previously not implicated in brain tumors. In addition, we identified 6 multi-fusion tumors. Rare fusions and multi-fusion events can impact the diagnostic accuracy of DNA methylation by decreasing confidence in the result, such as BRAF, RAF, or FGFR1 fusions, or result in a complete mismatch, such as NTRK, EWSR1, FGFR, and ALK fusions.

IMPLICATIONS

DNA methylation signatures need to be interpreted in the context of pathology and discordant results warrant testing for novel and rare gene fusions.

Progression-Free Survival in Patients with WHO-2 Meningioma Undergoing Active Surveillance Based on DOTATATE PET Evidence of Gross Total Resection: Prospective Observational Study

PURPOSE/OBJECTIVE(S)

MRI is the standard of care for meningioma radiotherapy planning, but lacks sensitivity for postoperative small volume disease and osseous or parenchymal invasion. NRG-BN003 (NCT03180268) randomizes patients with WHO-2 meningiomas and MRI-determined gross total resection (GTR) to observation or 60 Gy IMRT to the resection bed. More sensitive and specific imaging biomarkers than MRI may improve clinical outcomes in meningioma by limiting unnecessary irradiation of normal tissues and improving radiotherapy targeting. [68Ga]-DOTATATE, a PET radiotracer targeting somatostatin receptor 2 (SSTR2) is a highly sensitive and specific meningioma biomarker. Our dedicated DOTATATE brain PET/MRI and PET/CT protocol allows meningioma differentiation from post-treatment change, using SUV analysis and Patlak modeling. Our prospective IRB-approved observational trial (NCT04081701) has imaged >100 patients with meningioma. In the sub-analysis presented here, we prospectively evaluated PFS in patients with WHO-2 tumors and postoperative GTR as determined by [68Ga]-DOTATATE brain PET/MRI or PET/CT who were managed solely with active surveillance. We hypothesized that the PFS of patients with GTR by PET managed with active surveillance would be higher than reported PFS data for patients with MRI-determined GTR, using NRG-BN003's observation arm (randomized trial comparing observation to fractionated RT) as a reference standard.

MATERIALS/METHODS

From the cohort of >100 patients with SSTR2-positive brain neoplasms enrolled between 9/2019 and 10/2022 and imaged according to our previously published protocol, a sub-cohort of patients were selected with WHO-2 meningioma, postoperative findings of GTR, and postoperative active surveillance with periodic MRI every 3-6 months. Kaplan-Meier survival analysis was performed.

RESULTS

A total of 12 patients met inclusion criteria. Mean patient age was 64 years and 5 (42%) were female. Mean follow up period was 23.4 months (range: 7-38). 83% (10/12) patients underwent postoperative PET/MRI and 17% (2/12) underwent PET/CT. 2 patients (17%) progressed, at 22 and 34 months, respectively; the remainder remain progression-free. Both patients who had progression were successfully salvaged with focal fractionated radiosurgery. Kaplan-Meier analysis demonstrated PFS at almost 3 years to be 75%, which is substantially higher than the reported 3-year PFS of 60% in the literature. Overall survival was 100%.

CONCLUSION

[68Ga]-DOTATATE PET can improve the specificity of imaging-based assessment of the extent of resection of WHO-2 meningiomas, thereby improving clinical outcomes. In this cohort of patients with completely resected WHO-2 meningiomas (as assessed by postoperative gadolinium-enhanced MRI and DOTATATE PET) who are conservatively managed, recurrences have been rare and amenable to radiosurgical salvage.

Clinical utility of whole-genome DNA methylation profiling as a primary molecular diagnostic assay for central nervous system tumors-A prospective study and guidelines for clinical testing

Background

Central nervous system (CNS) cancer is the 10th leading cause of cancer-associated deaths for adults, but the leading cause in pediatric patients and young adults. The variety and complexity of histologic subtypes can lead to diagnostic errors. DNA methylation is an epigenetic modification that provides a tumor type-specific signature that can be used for diagnosis.

Methods

We performed a prospective study using DNA methylation analysis as a primary diagnostic method for 1921 brain tumors. All tumors received a pathology diagnosis and profiling by whole genome DNA methylation, followed by next-generation DNA and RNA sequencing. Results were stratified by concordance between DNA methylation and histopathology, establishing diagnostic utility.

Results

Of the 1602 cases with a World Health Organization histologic diagnosis, DNA methylation identified a diagnostic mismatch in 225 cases (14%), 78 cases (5%) did not classify with any class, and in an additional 110 (7%) cases DNA methylation confirmed the diagnosis and provided prognostic information. Of 319 cases carrying 195 different descriptive histologic diagnoses, DNA methylation provided a definitive diagnosis in 273 (86%) cases, separated them into 55 methylation classes, and changed the grading in 58 (18%) cases.

Conclusions

DNA methylation analysis is a robust method to diagnose primary CNS tumors, improving diagnostic accuracy, decreasing diagnostic errors and inconclusive diagnoses, and providing prognostic subclassification. This study provides a framework for inclusion of DNA methylation profiling as a primary molecular diagnostic test into professional guidelines for CNS tumors. The benefits include increased diagnostic accuracy, improved patient management, and refinements in clinical trial design.

Diffuse midline glioma with novel, potentially targetable, FGFR2-VPS35 fusion

We report a case of a slow-growing, diffuse, infiltrating glioma in the right brainstem of a 9-yr-old boy. The tumor was negative by immunohistochemical staining for histone H3 K27M, BRAF V600E, and IDH1 R132H mutations. Fluorescence in situ hybridization did not reveal a BRAF duplication. Genomic profiling of the tumor, by DNA methylation array and cancer whole-exome and transcriptome sequencing, was performed. This analysis showed copy-number alterations, including gains of several chromosomes. In addition, a novel fusion involving the first 17 exons of FGFR2 fused to exon 2 of VPS35 was identified. This novel fusion is predicted to result in activation of fibroblast growth factor receptor (FGFR) signaling and is potentially targetable using FGFR inhibitors. This tumor expands the spectrum of pediatric diffuse gliomas.