Presenter(s)
L. Greiner1, P. S. Chauhan1, C. Riviere-Cazaux2, J. L. Campian3, W. Breen1, T. Burns2, and A. A. Chaudhuri1; 1Department of Radiation Oncology, Mayo Clinic, Rochester, MN, 2Department of Neurosurgery, Mayo Clinic, Rochester, MN, 3Department of Medical Oncology, Mayo Clinic, Rochester, MN
Purpose/Objective(s):
Glioblastoma (GBM) is the most aggressive and malignant form of primary brain cancer. MRIs evaluated using the Response Assessment for Neuro-Oncology (RANO) 2.0 criteria are standard-of-care for assessing treatment response in GBM. However, up to 30% of cases exhibit increased contrast-enhancement on imaging without true disease progression, a phenomenon known as pseudoprogression. Differentiating pseudoprogression and other forms of radiation necrosis from true progression using imaging alone is challenging and often delays appropriate clinical management. Materials/Methods:
Previously biobanked paired plasma and cerebrospinal fluid (CSF) samples (n=63) from patients with primary GBM (n=15), recurrent GBM (n=11), and biopsy-proven pseudoprogression (n=5) were analyzed. Additional paired CSF samples were collected from brain metastases without prior radiation (n=8), recurrent brain metastases post-radiation (n=7), and biopsy-proven radiation necrosis (n=9). Control samples (n=8) from patients without evidence of GBM or brain metastases were also collected. Plasma samples were double-spun for 10 minutes at 4°C per standard practice with the supernatant collected and stored at -80°C until cell-free DNA isolation. CSF samples were centrifuged at 400 × g for 10 minutes at 4°C, and the supernatant was collected and stored at -80°C until cell-free DNA isolation. Cell-free DNA was extracted using a bead-based extraction kit, and concentrations, initially measured in ng/µL via Qubit fluorometry, were normalized to ng/mL plasma/CSF input before conversion to haploid genome equivalents per mL (hGE/mL) using the formula hGE/mL = (ng/mL) / (3.3 × 10?6 ng/hGE). These values were then compared across groups using one-way ANOVA followed by Tukey’s multiple comparison testing.
Results:
Cell-free DNA analysis of CSF revealed that samples from patients with brain metastases without prior radiation had significantly higher cfDNA concentrations (median: 6.68 * 106 hGE/mL) compared to primary GBM patients (median: 1.2 * 106 hGE/mL, p=0.02), recurrent GBM patients (median: 1.28 * 106 hGE/mL, p=0.03), radiation necrosis patients (median: 9.76 * 105 hGE/mL, p=0.04), and controls (median: 3.71*105 hGE/mL, p=0.05). In contrast, we observed no differences between groups when we measured cell-free DNA isolated from blood plasma.
Conclusion:
These promising findings using CSF, a proximal bioanalyte to central nervous system malignancy, lay the groundwork for future efforts to boost confidence in disease monitoring and clinical decision-making for patients with GBM.
