S374
Clinical - CNS
ESTRO 2026
Digital Poster 2809 Leptomeningeal Dissemination in High-Grade Glial Tumours: Incidence, Risk Factors and Survival Outcomes Serra Kamer 1 , Fethiye Odacı 1 , Cenk Eraslan 2 , Erkin Özgiray 3 , Yesim Ertan 4 , Taner Akalin 4 , Hüseyin Biçeroglu 3 , Cem Çallı 2 , Yavuz Anacak 1 1 Radiation Oncology, Ege university, İ zmir, Turkey. 2 Radiology, Ege university, İ zmir, Turkey. 3 Neurosurgery, Ege university, İ zmir, Turkey. 4 Pathology, Ege university, İ zmir, Turkey Purpose/Objective: High-grade glial tumours (HGG) are the most common primary brain tumours in adults. Despite multimodal treatment including surgical resection and adjuvant chemoradiotherapy, recurrence remains frequent. Leptomeningeal dissemination (LMD) represents a rare and poorly defined recurrence pattern. Data on its incidence and prognostic implications are limited. This study aimed to assess the incidence, risk factors, and survival outcomes associated with LMD in adult HGG patients treated at a single tertiary centre. Material/Methods: We retrospectively analysed 411 patients ( ≥ 18 years) diagnosed and treated for HGG between 2013 and 2023. Recurrence was confirmed radiologically or pathologically. Clinical and demographic characteristics, tumour localisation, histopathology, and molecular markers (IDH, ATRX, Ki-67, Olig2) were recorded. Associations between categorical variables were evaluated using the chi-square test. Survival was estimated using the Kaplan-Meier method, and comparisons were made with the log-rank test. Results: The median age was 55 years (range: 18–87), and the median follow-up time was 27 months (range: 4–144). The male-to-female ratio was 1.53. Tumor localization distribution was as follows: temporal (35%), frontal (30.9%), parietal (16.5%), multifocal (7.3%), occipital (4.8%), midline (4.1%), and infratentorial (1.2%).Histopathological subtypes included glioblastoma multiforme (GBM) in 323 patients (78.6%), anaplastic astrocytoma in 51 (12.4%), anaplastic oligodendroglioma in 30 (7.3%), gliosarcoma in 6 (1.4%), and anaplastic ganglioglioma in 1 (0.2%).During follow-up, 227 patients (55.2%) developed local recurrence, 104 (25.3%) multifocal recurrence, 29 (7.1%) leptomeningeal recurrence, 25 (6.1%) ependymal recurrence, while 26 (6.3%) remained recurrence-free.Overall survival (OS) rates were 58% at 1 year, 35% at 2 years, and 22% at 3 years. Univariate analysis revealed that younger age (<50 years), tumor localization, and histopathological subtype had a significant impact on survival (p=0.00).The mean time to recurrence was 14 months
performance status, and extent of surgery to minimize selection bias. Progression-free survival (PFS) and overall survival (OS) were analyzed using Cox proportional hazards models before and after PSM. Treatment-related toxicities were graded according to CTCAE v5.0. Results: A total of 321 patients were included (270 NFRT, 51 HFRT). Before adjustment, patients receiving HFRT were older (median 63 vs 58 years), had poorer performance status, and more frequently underwent biopsy only. Median PFS and OS were significantly shorter in the HFRT group before matching (6.2 vs 9.8 months, p=0.002; 9.5 vs 17.7 months, p<0.001). After PSM (n=76), survival differences were no longer significant (PFS 6.2 vs 7.4 months, p=0.156; OS 9.0 vs 11.6 months, p=0.189). MGMT promoter methylation and younger age remained independent prognostic factors for improved outcomes. HFRT showed a more favorable tolerability profile, with fewer hematologic and neurological toxicities, and lower treatment discontinuation rates. Conclusion: In younger GBM patients with biopsy or incomplete resection, HFRT was associated with worse unadjusted survival but comparable outcomes to NFRT after adjustment for baseline characteristics. HFRT may therefore represent a pragmatic, better-tolerated option for younger patients with poor performance status or limited therapeutic options, while NFRT should remain the preferred standard when feasible. Prospective studies are warranted to better define the role of HFRT and identify optimal candidates for this approach. References: Omuro A JAMA 2013; Stupp R NEJM 2005, 2009, JAMA 2017; Krigers A Front Neurol 2022; Vymazal J Front Oncol 2022; Roa W JCO 2004, 2015; Malmström A Lancet Oncol 2012; Perry JR NEJM 2017; Hingorani M BJR 2012; Trone JC Radiat Oncol 2020; Liao G Front Oncol 2019; Mak KS Cancer Med 2017; Navarria P Oncotarget 2017; Mallick S J Neurooncol 2018; Patel SI IJROBP 2021; Chidley P J Neurooncol 2022; Kim N Yonsei Med J 2023; Louis DN Neuro Oncol 2021; Lacroix M J Neurosurg 2001; Niyazi M Radiother Oncol 2016; Chang EL IJROBP 2007; Noël G Cancer Radiother 2011, 2016; Wick W Nat Rev Neurol 2014; Weller M Nat Rev Neurol 2010; Haque W Am J Clin Oncol 2018; Nead KT J Geriatr Oncol 2019. Keywords: glioblastoma, hypofractionation, young population
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