Glioblastoma is a highly aggressive and malignant form of brain cancer that arises from the glial cells of the brain. It is the most common and deadliest type of primary brain tumor in adults, with a very poor prognosis and a low survival rate. Glioblastoma is characterized by rapid and uncontrolled growth, infiltrative invasion into surrounding brain tissue, and resistance to standard treatments. Therefore, new therapeutic strategies are highly needed. A subpopulation of fibroblasts called "cancer-associated fibroblasts" (CAFs) is know to be a key constituent of tumor stroma in several non-CNS tumors (e.g., breast, colon, lung,ovarian, or pancreatic cancers) . These CAFs express a specific protein called "fibroblast activation protein" (FAP), which is usually not expressed in healthy adult mammalian tissues. FAP has been shown to be elevated in vitro and in situ in glioblastoma cells , suggesting that CAFs expressing FAP might also play a functional role in malignant brain tumors. This research project aims at better characterizing the links between areas of increased FAPI uptake within glioblastomas and the local level of tumor aggressiveness. This will be done by comparing the distribution of their anatomical locations uptake within the tumor with the distribution of the uptake of other markers of local tumor aggressiveness such as amino-acid PET (FET), and MRI measures of cerebral blood flow such as arterial spin labelling (ASL) or perfusion-weighted echo-planar images . Ultimately, when possible, neuroimaging data will be compared with pathology findings from targeted brain biopsy samples or material from ablative surgery. Furthermore, this study will provide the necessary first step towards more large scale studies evaluating the potential use of 177Lu-FAPI as therapeutic agent in glioblastoma.

Inclusion Criteria:

• Age above or equal to 18 years
• Patients with a brain lesion suspected of glioblastoma based on neuroimaging data or patients with suspected recurrence of glioblastoma
• ECOG performance status ≤ 3
• Signed Informed Consent form (ICF) obtained prior to any study related procedure.

Exclusion Criteria:

• Pregnant and/or lactating women.
• Subject with a significant medical, neuro-psychiatric, or surgical condition, currently uncontrolled by treatment, which, in the principal investigator's opinion, may interfere with completion of the study.
• Claustrophobic patient
• Known hypersensitivity reactions to the FAPI or to any excipients, or to gadolinium-based contrast agents (GBCAs).