GFAP and glioblastoma: CTC analysis methods for GBM, other than enumeration, include molecular profiling (e.g., next generation sequencing (NGS), Reverse Transcriptase-PCR (RT-PCR)), immunophenotyping using GBM-specific markers (such as GFAP, Nestin, Sox2, EGFR, GLAST) [21,28], single-cell sequencing [25], and epigenetic profiling [29], with CSF-based analysis often offering higher sensitivity than blood [30,31,32].