The gastrin-releasing peptide receptor (GRPr) is highly overexpressed in several solid tumors, including treatment-naïve and recurrent prostate cancer. [68Ga]Ga-RM2 is a well-established radiotracer for PET imaging of GRPr, and [177Lu]Lu-RM2 has been proposed as a therapeutic alternative for patients with heterogeneous and/or low expression of PSMA. In this study, we aimed to evaluate the expression of GRPr and PSMA in a group of patients diagnosed with castration-resistant prostate cancer (mCRPC) by means of PET imaging.
Seventeen mCRPC patients referred for radio-ligand therapy (RLT) were enrolled and underwent [68Ga]Ga-PSMA-11 and [68Ga]Ga-RM2 PET/CT imaging, 8.8 ± 8.6 days apart, to compare the biodistribution of each tracer. Uptake in healthy organs and tumor lesions was assessed by SUV values, and tumor-to-background ratios were analyzed.
[68Ga]Ga-PSMA-11 showed significantly higher uptake in tumor lesions in bone, lymph nodes, prostate, and soft tissues and detected 23% more lesions compared to [68Ga]Ga-RM2. In 4/17 patients (23.5%), the biodistribution of both tracers was comparable.
Our results show that in our cohort of mCRPC patients, PSMA expression was higher compared to GRPr. Nevertheless, RLT with [177Lu]Lu-RM2 may be an alternative treatment option for selected patients or patients in earlier disease stages, such as biochemical recurrence.
Cancers. 2023 Dec 29*** epublish ***
René Fernández, Cristian Soza-Ried, Andrei Iagaru, Andrew Stephens, Andre Müller, Hanno Schieferstein, Camilo Sandoval, Horacio Amaral, Vasko Kramer
Nuclear Medicine and PET/CT Center PositronMed, Providencia, Santiago 7501068, Chile., Department of Radiology, Division of Nuclear Medicine and Molecular Imaging, Stanford University, Stanford, CA 94305, USA., Life Molecular Imaging GmbH, 13353 Berlin, Germany., Formerly Piramal Imaging GmbH, 13353 Berlin, Germany., Fundación Arturo López Pérez, Providencia, Santiago 750069, Chile.