Clinical evaluation of (4S)-4-(3-[18F]Fluoropropyl)-L-glutamate (18F-FSPG) for PET/CT imaging in patients with newly diagnosed and recurrent prostate cancer.

PURPOSE (4S)-4-(3-[18F]Fluoropropyl)-L-glutamic acid (18F-FSPG) is a radiopharmaceutical for PET imaging of system xC- activity, which can be upregulated in prostate cancer. We present data on the first evaluation of newly diagnosed or recurrent prostate cancer patients with this radiopharmaceutical. EXPERIMENTAL DESIGN Ten primary and ten recurrent prostate cancer patients were enrolled in this prospective multicenter study. After injection of 300 MBq of 18F-FSPG, three whole-body PET/CT scans were obtained. Visual analysis was compared with step-section histopathology when available as well as other imaging studies and clinical outcomes. Metabolic parameters were measured semi-quantitatively. Expression levels of xCT and CD44 were evaluated by immunohistochemistry for patients with available tissue samples. RESULTS 18F-FSPG PET showed high tumor-to-background ratios with a relatively high tumor detection rate on a per-patient (89%) and per-lobe (87%) basis. The sensitivity was slightly higher with imaging at 105 minutes in comparison to 60 minutes. The SUVmax for cancer was significantly higher than both normal (p < 0.005) and benign pathology (p=0.011), while there was no significant difference between normal and benign pathology (p=0.120). In the setting of recurrence, agreement with standard imaging was demonstrated in 7 of 9 patients (78%) and 13 of 18 lesions (72%), and revealed true local recurrence in a discordant case. 18F-FSPG accumulation showed moderate correlation with CD44 expression. CONCLUSIONS 18F-FSPG is a promising tumor imaging agent for PET that seems to have favorable biodistribution and high cancer detection rate in patients with prostate cancer. Further studies are warranted to determine the diagnostic value for both initial staging and recurrence, and how it compares to other investigational radiotracers and conventional imaging modalities.