MP48-16: ¹⁸F-DCFPyL PSMA PET Imaging Improves Detection of Nodal Metastases in Comparison to Conventional Imaging in Patients with Locally Advanced or Oligometastatic Prostate Cancer

Ashanda Esdaille*, Edward Lawrence, Christos Kyriakopoulos, Brian Johnson, Alejandro Roldan-Alzate, Wei Huang, David Beebe, Hamid Emamekhoo, Shane Wells, Joshua Lang, Steve Cho, David Jarrard, Madison, WI

Introduction: NCCN guidelines recommend conventional imaging with CT, bone scan +/- MRI to identify extraprostatic disease in patients with high risk prostate cancer.  Interest has arisen in the use of prostate specific membrane antigen (PSMA) PET imaging to detect prostate cancer at metastatic sites using different tracers. Here, we examined the ability of 18F-DCFPyL (DCFPyL) PSMA-based PET imaging to detect nodal disease and compared this to conventional imaging in a cohort of men with locally advanced and/or oligometastatic prostate cancer (PCa).

Methods: UW17009 is an IRB-approved open-label, single-arm trial that recruited 30 patients with newly diagnosed advanced PCa.  Patients received ADT and docetaxel for three cycles (3 months) followed by radical prostatectomy (RP) and pelvic lymph node dissection (PLND). Exploratory interventions include PSMA PET/CT and MRI imaging as a method for determining treatment response and heterogeneity in primary PCa and metastatic lesions performed before and after chemohormonal therapy. Prior to randomization, patients received DCFPyL PET/CT and PET/MR imaging as well as conventional imaging, including CTs and Bone Scans. A mean dose of 7.86 mCi DCFPyL was administered. Whole-body PET/CT images (General Electric [GE] Discovery 710 PET/CT) were acquired starting at approximately 60 minutes after radiotracer injection followed by dedicated pelvic PET/MR and whole-body PET/MR (GE Signa PET/MR). PET imaging findings were compared to conventional dedicated CT imaging and were correlated to the results of final pathologic examination of each pelvic nodal dissection.

Results: 26 patients underwent conventional and exploratory imaging with subsequent neoadjuvant treatment, RP and PLND. The mean diagnostic PSA was 32.1 ng/dl and 88.5% had Gleason 9 PCa. Using standard conventional imaging, nodal disease was identified in 6/26 patients. Pelvic lymph node uptake was identified in 12/26 patients using DCFPyL-based PSMA PET. Initial correlation of the pathologic specimens with pre-treatment PSMA PET imaging revealed pelvic nodal metastatic PCa in 10/12 (83%) patients. On a per-lymph node packet basis (6 per patient), there were 156 evaluable regions, including 65 from patients with positive nodes. PSMA detected 14 packets that were positive for PCa and 102 packets that were negative on imaging and final pathology. Cancer was missed in 5 packets. The mean tumor size in the missed nodes was 2.3 mm (range 1-4 mm). For detecting cancer, calculated sensitivity was 73.7% (95% CI [48.8, 90.8), 85.7 % specificity (95% CI[78.1, 91.4]), and 95.3 % negative predictive value (95% CI[90.5, 97.7]).

Conclusions: In comparison to conventional imaging, in this cohort of patients, DCFPyL PSMA-based PET imaging identified nodal positive disease at twice the rate and when evaluating on a per-packet basis, there was high negative predictive value. Ongoing analysis of post-chemohormonal therapy PET imaging may provide more information regarding tumor response in this cohort.

Source of Funding: DOD IMPACT Award 191341- Partnering PI (J.L., D.J., D.B)