Abstract A65: Longitudinal detection of TERT-mutant plasma cell-free circulating tumor DNA in newly diagnosed glioblastoma patients

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Abstract Introduction: Liquid biopsies, especially plasma cell-free circulating tumor DNA (ctDNA), provide a potential opportunity to be a noninvasive biomarker for the diagnosis and monitoring of glioblastoma (GBM) patients. Previously, we detected TERT promoter hotspot mutations (C228T and C250T) in ctDNA of IDH wild-type (IDHwt) TERT promoter mutant GBM patients with 100% specificity using mutation-specific droplet digital PCR (ddPCR) assays. Here, we examine the association between mutant TERT ctDNA levels and clinical outcomes in newly diagnosed GBM patients undergoing chemoradiation. Methods: We analyzed 76 serially collected plasma samples from 17 patients with suspected IDHwt GBM based on MRI before surgery. Twenty mL of whole blood was collected in EDTA tubes at predetermined times: pre- and postoperatively, at the end of chemoradiation, and 1, 3, and 6 months from the end of chemoradiation. TERT promoter mutations C228T or C250T were identified in FFPE tumor samples using ddPCR assays specific for these mutations. Plasma samples were analyzed for the patient’s tumor TERT mutation using the ddPCR assays. The analytically validated thresholds for positive ctDNA detection were 1.5 and 1.7 copies/mL for C228T and C250T, respectively. Results: Sixteen of 17 (94%) IDHwt tumors had TERT mutations (10 C228T, 6 C250T) with MGMT methylated, unmethylated, or unknown status in 10, 5, and 1, respectively. Fourteen of the 16 patients (87.5%) had detectable mutant ctDNA at one or more time points (range 1.66 to 22.13 copies/mL). Of the 2 patients with undetectable ctDNA, one had diffuse and non-avidly enhancing disease and the other only had pre/postop plasma samples collected. Six patients had detectable ctDNA preop, and most had a dominant rim-enhancing mass with additional nonenhancing or enhancing lesion(s). Ten patients had detectable ctDNA up to 4 days postop, half of whom had undergone gross total resection. For 3 of 5 patients for whom there was a question of pseudoprogression versus true progression, ctDNA kinetics matched the clinical outcome. One patient with MGMT unmethylated multifocal GBM achieved ctDNA zeroconversion at 6 months post radiation (RT), and did not progress for another five months. Another patient was negative at all time points until their 3-month post RT follow-up, at which time they developed a recurrence. Another patient achieved zeroconversion at the end of RT but developed a borderline positive ctDNA at 6 months after RT, 2 months before documented radiographic progression. Conclusions: In this pilot, prospective ctDNA monitoring study of IDHwt GBM, TERT mutant ctDNA was detected at one or more time points in the majority of patients. ctDNA kinetics were associated with clinical outcomes for some patients. These data suggest that additional, larger studies could refine how ctDNA monitoring may be used to enhance the clinical management of IDHwt GBM patients. Citation Format: Christine Cordova, Mahrukh M. Syeda, Broderick Corless, Jennifer M. Wiggins, Amie Patel, Sylvia C. Kurz, Malcolm Delara, Zacharia Sawaged, Minerva Utate, Dimitris Placantonakis, John Golfinos, Jessica Schafrick, Joshua S. Silverman, Rajan Jain, Matija Snuderl, David Zagzag, George Karlin-Neumann, David Polsky, Andrew S. Chi. Longitudinal detection of TERT-mutant plasma cell-free circulating tumor DNA in newly diagnosed glioblastoma patients [abstract]. In: Proceedings of the AACR Special Conference on Advances in Liquid Biopsies; Jan 13-16, 2020; Miami, FL. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(11_Suppl):Abstract nr A65.