Pilot study of dual imaging with 89Zr-IAB2M and 68Ga-PSMA-11 PET/CT prior to prostatectomy.

Abstract

90 Background: Due to high expression of Prostate Specific Membrane Antigen (PSMA), it’s an excellent candidate for targeted molecular imaging. 89Zr-df-IAB2M is a J591 antibody derived minibody and 68Ga-PSMA-11 is a PSMA small molecule. Methods: Patients with clinically significant (defined as: ≥ 0.5 cm3 with Gleason pattern ≥ 4) localized prostate cancer (PCa) on conventional imaging modalities who planned to undergo surgery were imaged by PET/CT 1-3 hours after 5±2mCi of 68Ga-PSMA-11 injection and 89Zr-IAB2M PET 2-4 days after 10mg IAB2M labeled with 2.5 mCi of 89Zr injection. Image results were interpreted by a central reader without knowledge of the surgical pathology, mapped and the mapped findings later compared with surgical pathology map. Results: 9 patients having clinically localized PCa with median age 65 (46-79) and PSA 8.42 (1.6-12.2) were enrolled. All dominant PCa lesions, which had a median Gleason score 8 (6-9), were detected by both IAB2M and PSMA-11. The smallest of these dominant lesions was 8mm in size. Median SUVmax for dominant lesions was 3.3 (2.3-7.5) on IAB2M and 7.1 (1.6-23.2) on PSMA-11; median MR PIRADS was 4 (4-5). Of 9 Gleason 6 lesions identified on pathology, PSMA-11 detected 3 and IAB2M detected 2. Four extra-prostatic lesions in one patient were detected by both PET agents, 3 were confirmed by surgical pathology and 1 confirmed on bone scan 2 months post-op. A total of 8 lesions reported on scans were not reported by path: 3 were false positive on both scans, 3 were false positive on IAB2M scan only and 2 were false positive on PSMA-11 scan only. 5 Gleason 6 and 2 Gleason 3+4 lesions on pathology were missed by both PET agents and could be considered false negatives. Conclusions: In this small pilot series, performance of the both PET agents was very similar. An advantage of IAB2M is its hepatobiliary clearance rather than renal/urinary, which makes it potentially easier to visualize the PCa and/or pelvic disease; an advantage of PSMA-11 is the ability to image within 1 hour. Clinical trial information: NCT03675451.