Increased Uptake of 18F-THK5351 in Glioblastoma But Not in Metastatic Brain Tumor

18 F-THK5351 was developed as a tracer with high binding affinity and selectivity for tau protein. However, its off-target binding to monoamine oxidase B (MAO-B), an enzyme highly expressed in astrocytes, has also been demonstrated. In the case of glioblastoma, a strong accumulation of both 11 C-methionine (MET) and 18 F-THK5351 was observed in the tumor. Conversely, in the case of metastatic brain tumor, while 11 C-MET PET showed strong uptake in the lesion, 18 F-THK5351 PET revealed no significant accumulation. Differentiating solitary metastatic brain tumors from glioblastoma on MRI can be challenging. This report suggests that 18 F-THK5351 PET might serve as a valuable tool for distinguishing glioblastoma from metastatic brain tumors.