Comparative Detection of IDH1 R132H and TERT Promoter Mutations in Plasma and Cerebrospinal Fluid of Patients with Glioma Using Targeted Droplet Digital PCR

Background/Objectives: Molecular profiling is essential for glioma classification, but in some cases tissue sampling may be limited, whereas reported detectability of cell-free tumor DNA (cftDNA) in plasma and cerebrospinal fluid (CSF) varies considerably. The aim of this study was to compare the detection rates and concentrations of cftDNA carrying IDH1 R132H and TERT promoter C228T/C250T mutations in paired plasma and CSF samples, as well as to examine associated clinical characteristics. Methods: 66 patients with WHO grade 1–4 gliomas were enrolled before surgery. Preoperative plasma and lumbar CSF were collected before tissue-damaging procedures. Cell-free DNA (cfDNA) was isolated from 5 mL of plasma and 2.5–5.0 mL of CSF and analyzed using mutation-specific droplet digital PCR (ddPCR) assays. Results: cfDNA was available from 65 CSF and 63 plasma samples. Total cfDNA concentration was lower in CSF than in plasma (medians: 434.1 vs. 1240.3 copies/mL; p < 0.001). Nevertheless, cftDNA carrying at least one of the assayed mutations was detected in 14/65 CSF samples (21.5%) and in 0/63 plasma samples (0.0%) (p < 0.001). IDH1 R132H was detected in 4.6% of CSF samples, and TERT promoter mutations were detected in 16.9%. Every CSF mutation with available paired tissue data was also identified in the corresponding tumor. Glioma grade 4 and contrast-enhancing tumors were associated with higher CSF cfDNA, cftDNA carrying at least one of the assayed mutations, and mutant allele fraction values (p < 0.05), whereas tumor size and localization were not significantly associated with these parameters (p > 0.05). Conclusions: With the presented targeted ddPCR workflow, lumbar CSF was substantially more informative than plasma for detecting the selected glioma-associated mutations. CSF cftDNA analysis may complement tissue profiling, although broader panels and larger prospective studies are needed to establish its clinical sensitivity.