A Study of 68Ga-GRP PET/CT for Imaging in Low and Intermediate Risk Prostate Cancer

Prostate cancer (PCa) is the second-most common cancer among men across the world, and a significant cause of death in many regions. Different stages of PCa directly affect both the therapeutic schedule and patient prognosis. Recommended imaging modalities for initial staging include computerized tomography (CT) scan, bone scan, and Magnetic Resonance Imaging (MRI). In addition to initial work-up, Gallium-68 prostate-specific membrane antigen positron emission tomography/computer tomography (68Ga-PSMA PET/CT) is a relatively new nuclear imaging modality, showing high sensitivity and specificity. Recently, several studies have investigated the role of 68Ga-PSMA PET/CT in a first-line diagnostic setting, especially in patients with high-risk and biochemically recurrent PCa. Therefore, PET imaging with 68Ga-PSMA may participate to optimize work-up in the staging of high-risk patients. Another family of radiopharmaceuticals aimed to target the Gastrin-Releasing Peptide Receptor (GRP-R) which is overexpressed in early stage PCa. Various radiolabeled GRP analogues have been developed and shown encouraging results as related to the detection of primary PCa in preclinical study. However, 68Ga-GRP failed to detect some bone metastases in hormone-refractory patients. A prospective study identified that GRPR expression is not associated with Gleason score (GS) and PSMA expression, suggesting that 68Ga-GRP and 68Ga-PSMA PET/CT may be complementary in various risks of PCa diagnosis. The aim of this pilot study is to compare 68Ga-PSMA PET/CT to 68Ga-GRP PET/CT in patients with PCa of low and intermediate risk to better understand how 68Ga-PSMA and 68Ga-GRP PET/CT could performed a primary lesion mapping and how 68Ga-PSMA and 68Ga-GRP PET/CT could be used (or combined) in clinical practice.