P14.12.A PLASMA CFDNA LIQUID BIOPSY IN THE FOLLOW-UP OF HIGH-GRADE GLIOMAS

Abstract BACKGROUND As highlighted by the 2021 WHO classification of brain tumors, molecular characterization of gliomas is now critical to complement histopathological evaluation. However, intratumor heterogeneity may lead to surgical specimens not being fully representative of the whole tumor. Moreover, given the invasiveness of surgery, tissue analyses are not repeatable over time, thus limiting the possibility to monitor the response to therapies. In this context, we investigated the potential value of plasmatic cell-free DNA (PcfDNA) as a non-invasive ‘liquid biopsy’ marker of disease evolution. MATERIAL AND METHODS Patients’ blood was collected at 4 time points (TP), in parallel to clinical follow-up. A reproducible pipeline was optimized for blood withdrawal, centrifugation, plasma storage, cfDNA extraction from plasma by QIAamp MinElute ccfDNA Midi Kit (Quiagen) and cfDNA fluorometric quantification by Qubit (Thermo Fisher Scientific). MRI volumes were segmented in T1+contrast and T2-FLAIR sequences. RESULTS Fifty-four high-grade glioma patients and 14 healthy controls were enrolled. Blood samples were collected from all 54 patients at radiological diagnosis before surgery (TP0), from 33 patients after surgery (TP1), from 21 patients after radio-chemotherapy(TP2), from 10 patients at the first radiological progression (TP3). At T0, a significantly higher concentration of PcfDNA was detected in patients than in controls. IDH-wild-type gliomas showed a trend toward higher PcfDNA when compared with IDH-mutant gliomas. Digital-droplet PCR, performed at T0on PcfDNA of 4 patients with IDH-mutations in tumor tissues, identified the same IDH1-R132H mutation in all cases. When PcfDNA at TP0 was compared to that at TP1 of the same patient (n=33), there was a significant reduction of plasmatic cfDNA after surgery, mirroring the extensive tumor-resection shown by MRI. Finally, PcfDNA was evaluated in 10 patients until their radiological progression. Interestingly, PcfDNA levels not only followed the same trend of the volumes of T2-FLAIR hyperintensities and T1 contrast-enhancements, but were also mirrored by the evolution of KPS and NANO scores. CONCLUSION Preliminary results suggest that PcfDNA content may be an informative tool to complement MRI during the follow-up of high-grade gliomas.