P15.01.A FET PET SENSITIVITY IN PRIMARY BRAIN TUMORS ACCORDING TO CNS WHO 2021: VALUE AND PITFALLS IN PRESURGICAL IMPLEMENTATION

Abstract

Abstract BACKGROUND FET PET imaging has emerged as a valuable tool in the characterization of unclear brain lesions that cannot be clearly diagnosed with conventional diagnostic METHODS .In 2021,the Central Nervous System(CNS) World Health Organization(WHO) introduced significant changes in the classification of CNS tumors.Notably,under the new classification,certain cases of glioma may be reclassified as glioblastoma.Unfortunately,a subset of gliomas,as defined by the 2016 WHO classification,may exhibit no detectable FET uptake and lack contrast enhancement on MRI,which can lead to underestimation of such tumors and potentially result in inappropriate treatment decisions. MATERIAL AND METHODS In this study,we conducted a retrospective analysis of all patients who underwent FET PET imaging of the brain between 2017 and 2021,prior to their first surgical brain intervention.We obtained the results from presurgical MRI scans and categorized the lesions based on whether they exhibited contrast media enhancement or not,in addition to the postsurgical histopathologic diagnosis.Our analysis focused on identifying the number of cases in which the diagnosis of malignancy was underestimated in the context of the WHO 2016 classification.To further investigate these cases,we conducted NGS and 850k-analysis to reclassify the results in accordance with the new classification.Finally,we assessed the number of cases that were underestimated using the new classification criteria. RESULTS After enrolling 85 patients,our study found that according to the 2016 classification,preoperative imaging underestimated malignancy in 14 cases (16%) where histopathological analysis revealed high-grade malignant brain tumors.In 32 cases (27%), the preoperative imaging correctly suggested a malignant tumor,which was later confirmed by histopathological analysis after surgery.Additionally,22 cases were suggested to be low grade or benign,which was confirmed by postsurgical tissue analysis. Further analysis revealed that some patients diagnosed with low-grade glioma according to the WHO 2016 classification actually had molecular glioblastomas after reclassification.The final results of this reclassification after the CNS WHO 2021 will be presented at the annual meeting. CONCLUSION The findings of this study suggest that presurgical brain imaging,as per the WHO 2016 classification,may underestimate the malignancy of unclear brain lesions in up to 16% of cases.Our initial analysis also indicates that this underestimation may be more prevalent when using the new WHO CNS classification from 2021.Therefore,caution is advised when recommending non-surgical follow-ups in such cases, as it may lead to incorrect treatment decisions and worse patient outcomes.