Prognostic Value of O-(2-[18F]-Fluoroethyl)-L-Tyrosine-Positron Emission Tomography Imaging for Histopathologic Characteristics and Progression-Free Survival in Patients with Low-Grade Glioma

Objective O-(2-[18F]-fluoroethyl)-L-tyrosine positron emission tomography (¹⁸F-FET-PET) imaging is applied for tumor grading, prognostic stratification, and diagnosis of tumor recurrence, especially in high-grade gliomas. Experience with ¹⁸F-FET-PET imaging in low-grade gliomas is limited. Therefore, the objective of the present study was to assess ¹⁸F-FET-PET tracer uptake in low-grade gliomas and to investigate possible correlations with contrast enhancement in magnetic resonance imaging (MRI) and histopathology. Methods A total of 65 patients (29 female, 36 male, median age 38 years) with newly diagnosed or recurrent low-grade gliomas for whom preoperative MRI and ¹⁸F-FET-PET imaging were available were included. Tumor entity, tumor location, as well as histopathology (isocitrate dehydrogenase [IDH] 1/2 mutation, Ki67, p53, oligodendroglial differentiation, 1p19q codeletion), and progression-free survival were assessed. ¹⁸F-FET-PET images were acquired and fused to MRI (T2-weighted fluid-attenuated inversion recovery) and tumor volume was measured in areas with a tumor-to-background ratio >1.3, >1.6, and >2.0 and in MRI. Results PET tracer uptake was observed in 78.5% of all World Health Organization Grade I and II tumors. ¹⁸F-FET uptake showed a high negative predictive value for oligodendroglial components and for 1p19q codeletion. No further significant correlation between histologic features, progression-free survival, or IDH1/2 mutation status and tracer uptake was observed. Conclusions We found that 78.5% of low-grade gliomas do show elevated tracer uptake in ¹⁸F-FET-PET imaging. Low-grade glioma without tracer uptake exclude oligodendroglial differentiation and 1p19q codeletion. Further differentiation between molecular subtypes is not possible with static ¹⁸F-FET-PET. No correlation of progression-free survival to tracer uptake and IDH1/2-mutation status was observed.