In summary, our study identified 13C-MRS-detectable HP 6PG produced from HP gluconolactone as a metabolic biomarker of TERT and its silencing in human GBM with TERT promoter mutations, adding another translatable biomarker to the armamentarium of imaging tools that can help improve the monitoring of targeted therapies and personalized treatment of GBM patients, and more broadly any cancer patients for whom TERT might be considered a therapeutic target. Here, TERT is linked to glioblastoma.