13/14 (92.9%) IDHwt tumors had TERT mutations (7 C228T and 6 C250T). Six of these thirteen (46%) pts had positive plasma TERT ctDNA preop (4 C228T, 2 C250T).Detected plasma TERT ctDNA in 46% of TERT mutant GBM pts before surgery and in 100% of pts with multiple contrast-enhancing lesions.TERT mutant ctDNA levels correlated with pseudoprogression or true disease progression and predicted progression before MRI. Here, TERT is linked to glioblastoma.