Prospective Study of the Radiolabeled GRPR Antagonist BAY86-7548 for Positron Emission Tomography/Computed Tomography Imaging of Newly Diagnosed Prostate Cancer

Background: Current imaging techniques may not detect all prostate cancer (PCa) lesions. Objective: To evaluate positron emission tomography (PET)/computed tomography (CT) using the radiolabeled GRPR antagonist probe BAY86-7548 (Ga-68-RM2) for localization of newly diagnosed PCa in comparison with multiparametric magnetic resonance imaging (mpMRI), histopathology, and immunohistochemistry (IHC). Design, setting, and participants: This was a prospective study of 16 men with biopsy-proven PCa (2 low, 8 intermediate, and 6 high risk). Ga-68-RM2 PET/CT was performed within 4 wk after mpMRI and within 2 wk before radical prostatectomy and extended bilateral pelvic lymph node dissection. Outcome measurements and statistical analysis: The presence of cancer was evaluated by blinded specialists using a 5-point Likert scale, with lesions scoring 4 or 5 considered positive, on Ga-68-RM2 PET/CT, mpMRI, and Ga-68-RM2 PET/CT-mpMRI fused images for each of 12 anatomic areas of the prostate. Whole-mount, step-section pathology served as the reference standard. Expression of GRPR and prostate-specific membrane antigen (PSMA) was analyzed via IHC of tumor paraffin sections. Results and limitations: Of 192 areas analyzed, 128 contained cancer. The sensitivity, specificity, and accuracy of Ga-68-RM2 PET/CT imaging and mpMRI did not differ significantly; fusing the images maximized the sensitivity and accuracy (852% and 83.9%, respectively) and averaged the specificity (813%). The area under the receiver operating characteristic curve was 0.76 for PET visual analysis, 0.72 for PET quantitative analysis, 0.76 for mpMRI, and 0.85 for combined PET/CT and mpMRI analysis. Ga-68-RM2 uptake did not correlate with Gleason score. IHC analysis revealed weaker staining for GRPR than for PSMA, and the expression of these markers was not correlated (r = 0.3882). The major limitation is the small sample size. Conclusions: Ga-68-RM2 PET/CT is promising for detection and localization of primary PCa, and complements mpMRI. GRPR expression appears to be independent from PSMA expression, suggesting that GRPR- and PSMA-targeted PET imaging may be complementary. Patient summary: This pilot prospective study shows that a positron emission tomography probe that binds to a marker of prostate cancer, GRPR, improves the ability of magnetic resonance imaging to detect prostate cancer. (C) 2018 Published by Elsevier B.V. on behalf of European Association of Urology.