Impact of Higher Cell-Free DNA Yields on Liquid Biopsy Testing in Glioblastoma Patients

Minimally invasive molecular profiling using cell-free DNA (cfDNA) is increasingly important to the management of cancer patients; however, low sensitivity remains a major limitation, particularly for brain tumor patients. Transiently attenuating cfDNA clearance from the body-thereby, allowing more cfDNA to be sampled-has been proposed to improve the performance of liquid biopsy diagnostics. However, there is a paucity of clinical data on the effect of higher cfDNA recovery. Here, we investigated the impact of collecting greater quantities of cfDNA on circulating tumor DNA (ctDNA) sensitivity in the "low-shedding" cancer type glioblastoma by analyzing up to approximately 15-fold more plasma than routinely obtained clinically.

We tested 70 plasma samples (median 17.0 mL, range 2.5-66.5) from 8 IDH-wild-type glioblastoma patients using an optimized version of the MAESTRO-Pool ctDNA assay. Results were compared with simulated single-blood-tube equivalents of cfDNA. ctDNA results were then compared with magnetic resonance imaging (MRI) and pathology assessments of true progression vs pseudoprogression in glioblastoma patients.

Larger cfDNA yields exhibited a doubling in ctDNA-positivity while achieving a median specificity of 99% and more precise ctDNA quantification. In 8 glioblastoma patients, ctDNA was detected in 88%, including at multiple timepoints in 6/7. In the setting of indeterminate progression by MRI, our data suggested that MAESTRO-Pool with large plasma volumes can help distinguish true glioblastoma progression from pseudoprogression.

Our findings provide a proof-of-principle that most glioblastomas shed ctDNA into plasma and that greater ctDNA yields could help improve liquid biopsies for "low-shedding" cancer types such as glioblastoma.