ECP 2023 Abstracts

S116 Virchows Archiv (2023) 483 (Suppl 1):S1–S391 13 Conclusion: IMT, FET::CREB fusion-positive may be under-recog- nized due to its broad morphological presentation, including cases with striking astroblastoma-like pattern and rare desmin negative cases. The diagnosis requires confirmation of FET::CREB fusion. Methylation profiling was inconclusive apart from a histologically typical AFH case with secondary extension into the intracranial space. While most tumours had no recurrence after complete surgical resection, a case with significant residual tumour and instable genome showed cerebro- spinal fluid seeding and multiple spinal tumour implants. PS-18-004 The integrated genomic and epigenomic landscape of gangliogliomas - retrospective analysis of a single-centre case series Z. Reisz*, R. Laxton, K. Eggleton, L. Bhaw, B. Clark, A. King, S. Al-Sarraj, I. Bodi *Clinical Neuropathology, King’s College Hospital NHS Foundation Trust, London, United Kingdom Background & objectives: Gangliogliomas are low-grade epilepsy associated tumours (LEAT) with frequent BRAF V600E mutation, however, rare cases with other MAPK pathway alterations or gene fusions have been recently reported. We present here the integrated histo-molecular classification of 47 cases. Methods: Retrospective analysis of a departmental CNS tumour data- base identified 47 cases with a histological diagnosis of ganglioglioma. Morphological features and immunostains were reviewed indepen- dently by two neuropathologists, and the cases were further investi- gated by multimodal panel (covering 305 DNA and 76 RNA targets) and methylation array (DKFZ, Brain classifier v12.5). The tumours were reclassified according to the 2021 WHO guidelines. Results: Most cases occurred in the temporal lobe (66%) with a mean age of 12.3 years and an even gender distribution. Twenty-three cases (48.9%) harboured BRAF p.V600E mutation. Two cases had BRAF insertion (p.V504_R506dup), 2 cases showed KRAS p.Q61K mutation and additional 3 cases harboured SLMAP::NTRK2 and KIAA1549::BRAF fusion. Methylation array profiled 5 of these cases as “MC Pilocytic astrocytoma, hemispheric” and 2 cases as “MC Ganglioglioma”. A tumour with FGFR2::SHTN1 fusion was reclassified as polymorphous low-grade neuroepithelial tumour of the young. An FGFR3::SH3GLB1 translocation with concomitant TERT promoter mutation and chr +7/-10 was detected in a long-standing parietal lobe tumour in a 72-year-old male, with a methylation profile of ganglioglioma. Conclusion: Precise distinction of gangliogliomas from other epilepsy associated tumours may be challenging due to overlapping morphologi- cal features. While our study confirmed hotspot BRAF p.V600E muta- tion in nearly half of the samples, the BRAF-wildtype tumours showed a rather heterogenous molecular spectrum, including BRAF insertions, KRAS mutations and NTRK2 or FGFR2/3 fusions. One case presented with concerning copy number changes and TERT promoter mutation, raising the possibility of glioblastoma. Further studies regarding the biological behaviour of these tumours are needed. PS-18-005 Whole genome sequencing - a single assay approach in paediatric brain tumour diagnostics Z. Reisz*, R. Laxton, K. Eggleton, L. Bhaw, S. Nevis, C. Limbachia, S. Allouni, H. Hanson, A. King, I. Bodi, B. Clark, S. Al-Sarraj *Clinical Neuropathology, King’s College Hospital NHS Foundation Trust, London, United Kingdom Background & objectives: Comprehensive molecular analysis is essential for accurate diagnosis of paediatric central nervous system tumours, which often requires parallel running of diverse testing methods. We evaluated the diagnostic utility of whole genome sequenc- ing (WGS) compared with a standard-of-care molecular panel. Methods: Fresh brain tumour samples from 40 paediatric patients (30 glial, 7 embryonal, 1 pineal, and 2 germ cell tumours) were analysed by a multimodal panel (covering 305 DNA and 76 RNA targets) and DNA methylation array (DKFZ). Comparative analysis with WGS data was performed including detection of diagnostic small nucleo- tide (SNVs) and structural variants and loss of heterozygosity (LOH). Results: Multimodal panel detected diagnostic variants in 77.5% of the cases, with a total of 48 pathogenic SNVs and 15 gene fusions. Nine cases had no driver molecular alterations, but all tumours were confidently profiled by methylation array. WGS confirmed 85.4% of the known pathogenic SNVs and found an additional 21 previously undiscovered variants and one pathogenic germline variant. All the diagnostic fusions were confirmed by WGS. Among the cases with no diagnostic alterations by the standard-of-care panel, WGS found 6 new SNVs and 2 gene fusions. Methylation array appeared sensi- tive for copy number variation assessment, apart from copy-neutral LOHs. The histological diagnosis was refined in 2 cases after molecu- lar investigation. Conclusion: WGS offers a single-test molecular approach with improved diagnostic utility over the standard-of-care gene panels, particularly in chal- lenging brain tumour cases. Limitations might include the requirement for fresh tissue, slower turn-around time due to time-consuming data analysis and the large number of variants of unknown clinical significance. The pos- sibility of missed SNVs and complex structural variants cannot be excluded, which may be resolved by future long-read sequencing techniques. PS-18-006 SOX11 immunohistochemistry in diagnosis of gliomas and reactive glioses J. Soukup*, L. Gerykova, P. Kasparova, Z. Pleskacova, J. Petera, V. Skarkova *University Hospital Hradec Kralove, Czech Republic Background & objectives: SOX11 is a transcription factor involved in neurogenesis. In current study, we assessed SOX11 immunoreactivity in large cohort of different reactive glial processes and neoplasms to evaluate SOX11 utility in diagnostic neuropathology. Methods: Tissue microarrays were constructed, with samples of reactive glioses (n=46), glioblastomas (GBMs, n=81), IDH1-mutant astrocytomas (IDH1-As, n=17), oligodendroglial tumours with 1p/19q- loss (OGs, n=17), ependymomas (EPs, n=10, including 2 subepend- ymomas), pilocytic astrocytomas (PAs, n=8 including one pilomyxoid astrocytoma) and gangliogliomas (GGs, n=5). SOX11 was detected in TMAs using monoclonal antibody MRQ-58 (1:50) on Ventana Bench- mark Ultra and analysed as H-score. Results: SOX11 was significantly more positive in gliomas compared to glioses (69.9% vs 20.4%, p<0.001). However, absence of SOX11+ cells was only 79.5% sensitive and 46.6% specific for diagnosis of reactive gliosis. We observed a consistent positivity of SOX11 in IDH1mt subset of gliomas (100%, 34/34) and a common positivity in GBMs (75%, 57/76). IDH1mt tumours showed significantly higher SOX11 expression compared to GBMs (median H-score 2 vs 25.8, p<0.001). There was no difference in SOX11 between IDH1-As and OGs. SOX11 expression in IDH1mt tumours was associated with tumour grade (medians H-score G2=7.5, G3=55, G4=47.6, p<0.001). Of other gliomas, SOX11 was observed in one PA and ependymoma (H-scores 1 and 10). Conclusion: IDH1-mutated tumours and GBMs are commonly SOX11 positive, compared to other glial neoplasms. Although glioses are posi- tive significantly less frequently, low sensitivity and specificity precludes SOX11 use as a general marker of glioma in limited samples. Funding: Ministry of Health, Czech Republic, project No. NU20-03-00360