ESTRO 2024 - Abstract Book

S864

Clinical - CNS

ESTRO 2024

Clinical outcomes in molecular characterization of Glioblastoma without histological features.

Nikunj Rajiv Patil 1 , Vibhay Pareek 1 , Sheen Dube 2 , Namita Sinha 3 , Jai Shankar 4 , Saranya Kakumanu 1

1 CancerCare Manitoba, Radiation Oncology, Winnipeg, Canada. 2 University of Winnipeg, Biochemistry, Winnipeg, Canada. 3 University of Manitoba, Pathology, Winnipeg, Canada. 4 University of Manitoba, Radiodiagnosis, Winnipeg, Canada

Purpose/Objective:

In 2021, WHO updated the classification of tumors of the central nervous system (1) and proposed three genetic parameters i.e. TERT promoter mutation, EGFR amplification, and concurrent gain of chromosome 7 and loss of chromosome 10, to establish the diagnosis of Glioblastoma even in the absence of evidence of high-grade histological features such as necrosis or microvascular proliferation (2-4). We describe the clinical and treatment characteristics for these patients with molecular glioblastoma (Mol-GBM) without evidence of high-grade histologic features and compare the survival outcomes with the patient, disease, and treatment characteristics.

Material/Methods:

Our study is a retrospective chart review of patients diagnosed with glioblastoma with TERTp mutation, EGFR amplification, and/ or concurrent gain of chromosome 7 and loss of chromosome 10 mutation and lacking high grade histologic features. The patients were treated at our centre between January 2017 and June 2023. The eligible patients were analyzed for their demographic variables and clinical, treatment, and survival outcomes. Progression free survival (PFS) was defined as the time from diagnosis to disease progression. Overall survival (OS) was defined as the time from diagnosis to death from any cause or date of last contact. Disease-specific survival (DSS) was the percentage of people who had not died from glioblastoma at the last follow-up. Association analysis between clinical, dosimetric, and outcome characteristics was done using an unpaired t-test for the normal independent variable; for nominal independent data, a Fisher test and Chi-square test were used, and Kaplan-Meier survival analysis was used to estimate PFS, OS, and DSS. A p-value of <0.05 was regarded as statistically significant. The median follow-up of 32 patients included in the study was 12 months, and the median age was 62 years (IRQ 40-82 years) with 68% (n=22) males. Temporal lobe was the most common site of tumor 12 (37%), followed by frontal lobe 10 (32%), and tissue diagnosis in twenty-seven (85%) patients were obtained by stereotactic biopsy. Only five (15%) patients underwent resection. All patients had no high-grade histological features, such as necrosis and/or microvascular proliferation. Molecular testing showed TERTp mutation in thirty patients (93%), concurrent gain of chromosome 7, and loss of chromosome 10 in two patients (7%). All patients were IDH-wild type. Only ten patients (32%) had MGMT promoter methylation. Radiological enhancement was seen in 13 patients (40%), multifocal disease in 9 (28%), and hemorrhage in 3 patients (9%). A majority (47%) received a dose of 60Gy in 30 fractions. A total of 27 patients (84 %) received concurrent temozolomide. The median volume of PTV was 343 cc. The median OS was 11.35 months (IRQ 2-35.2). The median OS in the MGMT methylated group was 17.43 months versus 8.85 in the unmethylated group (p<0.001). The median OS in patients who received a dose of 60Gy vs 40Gy was 13.2 months versus 10.7 months (p<0.01). The median OS in patients with a PTV volume less than 343 cc vs Results: