High-grade glial tumors imaging by means of gallium-68 fibroblast activation protein inhibitor-04 PET-computed tomography in correlation with histopathology fibroblast activation protein analysis.

Abstract

Aim: Gallium-68 fibroblast activation protein inhibitor-04 PET-computed tomography ( 68 Ga-FAPi-04 PET-CT) imaging is a promising modality with higher tumor affinity and lower background activity than 18 F-fluorodeoxyglucose, especially for brain imaging, which has no significant physiological uptake. This study aimed to determine the uptake of high-grade glioma lesions in correlation with histopathological FAP expression and to assess the contribution of imaging accordingly.

Materials and methods: Fifteen patients with high-grade gliomas (WHO grade 3 and 4) were the subjects of this study. The patients presented with suspicion of recurrent tumors, which were determined by MRI imaging. 68 Ga-FAPi-04 PET-CT was performed on all subjects. The images were analyzed by visual and quantitative evaluation, which was compared with FAP expression determined from the pathology specimens, and all results were compared with the follow-up results (progression) at 12.2 ± 14.6 months.

Results: PET-CT imaging revealed an area under the curve of 0.97 for the tumor-to-background ratio of 14.3, with 100% sensitivity and 88.9% specificity for predicting progression in this small patient cohort ( Fig. 1 ). In addition, whole-body imaging revealed suspicion of bone metastasis in three patients and liver metastasis in one patient, but validation was not possible because of short survival after imaging.

Conclusion: Although the sample size is limited, Ga-FAPi-04 PET-CT imaging showed high diagnostic value for recurrent tumors, as tumor-to-background ratio values correlate with prognosis. In addition, a theranostic approach using these radiopharmaceuticals might yield favorable results in further studies.