Beyond the blood-brain barrier: feasibility and technical validation of dual-compartment circulating tumor cells detection in high-grade glioma patients

The elusive nature of brain tumor progression, hidden behind the blood-brain barrier, presents significant challenges for treatment monitoring in high-grade gliomas. In this feasibility study, we evaluate a novel approach to tracking glioblastoma through liquid biopsy, assessing whether tumor cells leave detectable molecular footprints in both blood and cerebrospinal fluid (CSF). Using the MiSelect R II System with specialized microfluidic technology, we analyzed paired blood and CSF samples from six glioblastoma patients, revealing a striking presence of circulating tumor cells (CTCs)- with higher abundance in CSF, where detection rates reached 100% compared to 83.3% in blood. Our technical validation demonstrates the system's capability to identify CTCs through multi-marker analysis (EGFR+/GFAP+/CD45-). Preliminary observations revealed higher CTC counts in CSF (median 15.5 cells/mL) compared to blood (median 3.0 cells/mL), with notable differences between compartments suggesting they may reflect distinct aspects of disease biology. In a patient who developed progressive disease, we observed a substantial increase in CSF CTCs from 14 to 116 cells/mL, warranting further investigation in larger cohorts. Additionally, we detected CTC clusters in both compartments, an intriguing finding with potential biological significance. While our interim analysis provides technical proof-of-concept for CTC detection in glioblastoma patients, the limited sample size precludes definitive conclusions regarding clinical utility. These findings establish a methodological foundation for future comprehensive studies exploring the relationship between CTC dynamics and clinical outcomes in high-grade gliomas.