Circulating Biomarkers for Tumour Monitoring, Prognosis Predictions and Detection of Temozolomide Resistance Mutations in Glioma

INTRODUCTION: The potential benefits of circulating biomarkers have been well demonstrated in other cancers. Despite this, no circulating biomarker exists for glioma due to poor sensitivity and hetereogeneity of results. METHODS: Serum miRNA and plasma ctDNA was isolated in a cohort of 212 gliomas using next-generation sequencing (NGS) and digital droplet PCR (ddPCR). Differentially expressed miRNAs were discovered using a machine learning algorithm and compared to tumor volume on MRI. A Lasso-regression model identified miRNAs that were associated with both progression-free and overall survival. Tumor mutations and ctDNA was compared in 49 plasma samples from 10 patients with tumor tissue available from at least two operations using NGS. Identified mutations were validated using ddPCR in the whole cohort. RESULTS: A 9-gene miRNA signature was found that could distinguish between glioma and healthy controls with 99.8% accuracy, including two that demonstrated dynamic changes that correlated with tumor volume on MRI. We found a separate 4-gene miRNA signature that was predictive of survival outcomes and could be incorporated into a clinical nomogram. Common glioma mutations were identified within 93% of plasma samples, including 25% that were not found in the tumor tissue. Mutations in the mismatch repair genes (MMR) were frequently detected in the plasma following temozolomide treatment and observed prior to their appearance in tissue at progression. CONCLUSIONS: We have identified serum miRNA biomarker signatures that can monitor tumour burden and improve prognostic predictions. We also show that contrary to previous reports, ctDNA can be reliably detected in the plasma of gliomas. We found that ctDNA offers complementary information to tissue biopsy alone and provides early evidence of temozolomide resistance through mutations in MMR genes.