High-uptake areas on positron emission tomography with the hypoxic radiotracer 18F-FRP170 in glioblastomas include regions retaining proliferative activity under hypoxia

The aim was to evaluate the proliferative activity of high-uptake areas on positron emission tomography (PET) with the hypoxic cell radiotracer, 1-(2-[F-18]fluoro-1-[hydroxymethyl]ethoxy)methyl-2-nitroimidazole (FRP170). Thirteen patients with glioblastoma underwent FRP170 PET before tumor resection. During surgery, tumor specimens were stereotaxically obtained from regions corresponding to high (high-uptake areas, HUAs) and relatively low (low-uptake areas, LUAs) accumulation of FRP170. We compared immunohistochemical staining for Ki-67 and hypoxia-inducible factor (HIF)-1 alpha between HUA and LUA. HIF-1 alpha index was significantly higher in HUAs than in LUAs. In contrast, mean Ki-67 indices did not differ significantly between HUAs and LUAs. Findings for HIF-1 alpha index clearly indicated that HUAs on FRP170 PET represented hypoxic regions in glioblastoma. However, findings of Ki-67 index suggest that HUAs on FRP170 PET include regions retaining proliferative activity regardless of tissue hypoxia.