Voxel-based comparison of [68Ga]Ga-RM2-PET/CT and [68Ga]Ga-PSMA-11-PET/CT with histopathology for diagnosis of primary prostate cancer

Thomas Franz Fassbender; Florian Schiller; Constantinos Zamboglou; Vanessa Drendel; Selina Kiefer; Cordula A Jilg; Anca-Ligia Grosu; Michael Mix

doi:10.1186/s13550-020-00652-y

Voxel-based comparison of [⁶⁸Ga]Ga-RM2-PET/CT and [⁶⁸Ga]Ga-PSMA-11-PET/CT with histopathology for diagnosis of primary prostate cancer

EJNMMI Res. 2020 Jun 12;10(1):62. doi: 10.1186/s13550-020-00652-y.

Authors

Thomas Franz Fassbender¹, Florian Schiller², Constantinos Zamboglou^{3

4

5}, Vanessa Drendel⁶, Selina Kiefer⁶, Cordula A Jilg⁷, Anca-Ligia Grosu^{3

4}, Michael Mix²

Affiliations

¹ Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany. thomas.fassbender@uniklinik-freiburg.de.
² Department of Nuclear Medicine, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
³ Department of Radiation Oncology, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
⁴ German Cancer Consortium (DKTK), Partner Site Freiburg, Freiburg, Germany.
⁵ Berta-Ottenstein-Programme, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
⁶ Department of Pathology, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.
⁷ Department of Urology, Medical Center - University of Freiburg, Faculty of Medicine, University of Freiburg, Freiburg, Germany.

Abstract

Background: Focal therapies or focally escalated therapies of primary prostate cancer are becoming more and more important. This increases the need to identify the exact extension of the intraprostatic tumor and possible dominant intraprostatic lesions by imaging techniques. While the prostate-specific membrane antigen (PSMA) is already a well-established target for imaging of prostate cancer cells, the gastrin-releasing peptide receptor (GRPR) seems to provide interesting additional information. Histopathology was used to examine the extent to which the single and combined image information of PET scans targeting GRPR and PSMA might lead to better tumor delineation.

Methods: Eight patients with histologically proven primary prostate cancer underwent two positron emission tomography with computer tomography scans, [⁶⁸Ga]Ga-RM2-PET/CT (RM2-PET) and [⁶⁸Ga]Ga-PSMA-11-PET/CT (PSMA-PET), prior to radical prostatectomy. RM2-PET data were correlated voxel-wise to a voxel-based model of the histopathologic tumor volume information. The results were compared to, correlated to, and combined with the correlation of PSMA-PET data analyzed analogously.

Results: In 4/8 patients, RM2-PET showed a higher signal in histologically proven tumor regions compared to PSMA. There were also tumor regions where PSMA-PET showed a higher signal than GRPR in 4/8 patients. A voxel-wise correlation of RM2-PET against histopathology yielded similar results compared to the correlation of PSMA-PET against histopathology, while PSMA-PET is the slightly better performing imaging technique. The combined information of both tracers yielded the best overall result, although this effect was not statistically significant compared to RM2-PET alone.

Conclusions: Qualitative and quantitative findings in this preliminary study with 8 patients indicate that RM2-PET and PSMA-PET partially show not only the same, but also distinct regions of prostate cancer. Patients with pPCa might profit from information given by tracers targeting GRPR and PSMA simultaneously, in terms of a better delineation of the gross tumor volume.

Keywords: Bombesin; GRPR; PET/CT; PSMA; Prostate cancer; RM2.