For this prospective, single arm, phase II clinical trial, men with Gleason grade ≥4+3, negative conventional staging, and scheduled for robotic prostatectomy were screened for inclusion. Enrolled patients received a 68Ga-PSMA-11 PET-CT scan for preoperative staging. Intraoperatively, 68Ga-PSMA-11 was re-dosed 30-60 min before taking the prostatic pedicle, and the extirpated prostate specimen was scanned with a high-resolution (1mm) small bore animal PET scanner. A subset of patients (n=5) had their specimen bivalved and evaluated with a 3mm beta-ray hand probe. The prostate was evaluated with whole-mount pathologic processing for intra-lesion analysis and registration with PET imaging. As follows is a representation of the preop PSMA PET-CT, ex-vivo PSAM PET on the prostate gland, and the whole mount pathology correlation:
The median age of 10 patients enrolled was 63.5 years and median PSA was 8.1ng/mL.
The final pathologic Gleason was: 4+5/5+4 (n=4), 4+3 (n=3), and 3+4 (n=3). Positive PET lesions were seen all 10 cases. Stratifying detection by Gleason, all ≥Gleason 4+3 cases were detected by PSMA-PET, whereas 2/3 of Gleason 3+3 cases were detected. The staging PSMA-PET accurately predicted seminal vesicle invasion (pT3b) in 4a of 5 patients and 5 of 5 when utilizing the immediate postoperative high-resolution scanner. The staging PSMA-PET accurately predicted 1 of 2 lymph node invasions. The detected node was 6mm and the missed node was 2mm. The median (IQR) SUVmax for intraprostatic cancer was 10.6 (8-13) and for benign prostate was 3.8 (3-5). The PSMA-PET images showed good registration with whole-mount pathology for Gleason ≥4+3 (n=7). For Gleason 3+4 (n=3), PSMA-PET detected lesions with %pattern 4 of 20% and 30% while missing a 10% pattern 4. Gleason pattern 3 was not seen by PSMA-PET. Unfortunately, the beta hand probe did not consistently detect positive cancer margins.
Dr. Bahler concluded that based on this pilot study, 68Ga-PSMA-11 clinical staging could aid in surgical planning as it accurately detected Gleason patterns ≥4+3 and predicted seminal vesical invasion. Further study is needed to determine the minimal % pattern 4 that can be detected with PSMA-PET. Dr. Bahler finished with a quote from one of his radiology colleagues “Reading prostate MRI is solving a puzzle. PSMA is like looking at the back page to read the answer.
Presented by: Clinton Bahler, Indiana University, Indianapolis, IN
Co-Authors: Mark Green, Gary Hutchins, Liang Cheng, James Fletcher, Temel Tirkes, Michael Koch, Indianapolis, IN
References:
1. Koerber SA, Utzinger MT, Kratochwil C, et al. 68Ga-PSAM-11 PETCT in newly diagnosed carcinoma of the prostate: Correlation of Intraprostatic PSMA uptake with several clinical parameters. J Nucl Med 2017;58(12):1943-1948.
Written by: Zachary Klaassen, MD, Urologic Oncology Fellow, University of Toronto, Princess Margaret Cancer Centre at the 2018 AUA Annual Meeting - May 18 - 21, 2018 – San Francisco, CA USA