Molecular testing using blood-based liquid biopsy approaches has not been widely investigated in patients with glioma. A prospective single-center study enrolled patients with gliomas ranging from grade II to IV. Peripheral blood (PB) was drawn at different timepoints for circulating tumour DNA (ctDNA) monitoring. Next-generation sequencing (NGS) was used for the study of isocitrate dehydrogenase 1 (IDH1) mutations in the primary tumor. Beads, Emulsion, Amplification and Magnetics (BEAMing) was used for the study of IDH1 mutations in plasma and correlated with the NGS results in the tumor. Between February 2017 and July 2018, ten patients were enrolled, six with IDH1-mutant and four with IDH1 wild-type gliomas. Among the six IDH-mutant gliomas, three had the same IDH1 mutation detected in plasma (50%), and the IDH1-positive ctDNA result was obtained in patients either at diagnosis (no treatment) or during progressive disease. While the false-negative rate reached 86% (18/21), 15 out of the 18 (83%) plasma-negative results were from PB collected from the six IDH-mutant patients at times at which there was no accompanying evidence of tumor progression, as assessed by MRI. There were no false-positive cases in plasma collected from patients with IDH1 wild-type tumors. BEAMing detected IDH1 mutations in the plasma of patients with gliomas, with a modest clinical sensitivity (true positivity rate) but with 100% clinical specificity, with complete agreement between the mutant loci detected in tumor and plasma. Larger prospective studies should be conducted to expand on these findings, and further explore the clearance of mutations in PB from IDH1-positive patients in response to therapy.
69 Background: Plasma immune biomarkers such as soluble plasma PD-L1 (sPD-L1) may serve as surrogates of the immune condition of cancer patients and be potential markers of response to different immunotherapy modalities. Very few data exist regarding sPD-L1 in patients with primary brain tumors. Our aim was to study the levels of sPD-L1 in patients with gliomas according to histologic grade and IDH mutation status. Methods: Patients (pts) with grade II to IV gliomas were prospectively enrolled. Single-time-point plasma samples were obtained prior to adjuvant radiotherapy +/- chemotherapy. sPD-L1 determined using ELISA with a rabbit polyclonal anti-PDL1/CD274 antibody as capture reagent. Results: Between February 2017 and August 2019, 44 patients (pts) with gliomas and 12 healthy controls (HC) were enrolled. N=11 grade II, n=9 grade III, n=24 grade IV; n=26 IDHwt, n=18 IDHmut. Higher sPD-L1 levels in glioma pts compared to HC (60.8 vs 47.8 ng/ml, p=0.05). Higher sPD-L1 levels in grade II vs grades III-IV (73.3 vs 60 ng/ml, p=0.09). Higher sPD-L1 in IDHmut grades II-III vs IDHwt grades II-III + IDHmut/wt grade IV (73 vs 59 ng/ml, p=0.07). Non-significantly higher sPD-L1 in grades II-III vs grade IV (73 vs 59 ng/ml, p=0.46). No difference in sPD-L1 in IDHmut vs IDHwt (63.3 vs 59.1 ng/ml, p=0.496), nor in IDHwt vs HC (59.1 vs 47.8 ng/ml, p=0.109). Trend to significance in IDHmut vs HC (63.3 vs 47.8, p=0.062). Conclusions: sPD-L1 levels were significantly higher in glioma pts compared to HC. A trend was seen towards higher sPD-L1 levels in lower-grade (grades II, III) IDHmut gliomas. These findings may indicate a different systemic immune profile for currently defined glioma groups based on histologic grade and IDH status and merit confirmation in a larger sample.
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