SNMMI 2021: A Phase 3 Study of 18F-DCFPyL-PET/CT in Patients With Biochemically Recurrence Prostate Cancer (CONDOR): An Analysis of Disease Detection Rate and Positive Predictive Value by Anatomic Region

(UroToday.com) PSMA-targeted PET/CT is superior to conventional imaging modalities to localize biochemically recurrent prostate cancer after local therapy, particularly in patients with low PSA (< 2 ng/mL) values. However, few studies have reported PSMA-targeted PET/CT accuracy compared to a pre-specified rigorous standard of truth including histopathology, correlative imaging, or treatment response in this population. The previously published CONDOR study focused on patients with biochemically recurrent disease, with a rising PSA after definitive therapy and negative or equivocal standard of care imaging (e.g., CT/MRI, bone scintigraphy, or F-18 fluciclovine).1 In this study, PyL-PET/CT correctly localized lesions in 84.8-87.0% of cases among three readers (lower bound of 95% CI: 77.8%-80.4%) against the composite standard of truth. At the 2021 SNMMI virtual annual meeting, Dr. Steven Rowe and colleagues presented results of the positive predictive value and detection rate of 18F-DCFPyL-PET/CT by anatomic region: prostate/prostate bed, pelvic lymph nodes, and extra-pelvic regions (including lymph nodes, bone, and viscera/soft tissue).

The study design for CONDOR is as follows:

CONDORpic1.jpg

For this study, a single 9 mCi (333 MBq) ± 20% dose of 18F-DCFPyL was injected, followed by PET/CT 1-2 hours later. Patients with positive 18F-DCFPyL-PET/CT scans based on local interpretation were scheduled for follow-up within 60 days to verify suspected lesion(s) using a composite standard of truth. The primary endpoint was the correct localization rate defined as positive predictive value with the requirement of anatomic lesion co-localization between 18F-DCFPyL-PET/CT and the standard of truth. The standard of truth consisted of, in descending priority:
  1. Histopathology
  2. Subsequent correlative imaging findings determined by two central readers
  3. Post radiation PSA response
The positive predictive value within anatomic regions without lesion-level matching was calculated for patients with positive 18F-DCFPyL-PET/CT as true positive/(true positive + false positive) × 100%. The disease detection rate was defined as the percent of positive 18F-DCFPyL-PET/CT scans identified by each central imaging reader and was calculated as the number of patients with positive scans divided by the number of patients scanned × 100%.

There were 208 men (median: PSA 0.8 ng/mL; range: 0.17 to 98.45) that underwent 18F-DCFPyL-PET/CT and the primary endpoint was met. The median positive predictive value (≥1 lesion confirmed) of three independent readers for 18F-DCFPyL-PET/CT by anatomic region was: 31/39 (79.5%, CI: 66.8-92.2%) for prostate/prostate bed, 39/55 (70.9%, CI 58.9-82.9) for pelvic lymph nodes, and 31/46 (67.4%, CI 53.8-80.9) for extra-pelvic region:

CONDORpic2.png

Median detection rates (n = 208) for prostate/prostate bed, lymph nodes and extra-pelvic region were: 20.2% (CI 14.7-25.6), 35.1% (CI 28.6-41.6%), and 26.4% (CI 20.4-32.4%), respectively. Further analyses of the extra-pelvic region results showed median positive predictive values of 16/26 (61.5%, CI 42.8-80.2) for lymph nodes (M1a), 15/24 (62.5%, CI 43.1-81.9) for bone (M1b), and 2/7 (28.6%, CI 7.6-64.8%) for visceral/soft tissue (M1c):

CONDORpic3.png

Dr. Rowe concluded this subanalysis of the CONDOR trial with the following summary points:
• 18F-DCFPyL-PET/CT detected and localized metastatic lesions with high positive predictive value regardless of the anatomic region in men with biochemically recurrent prostate cancer who had negative or equivocal baseline imaging
• Higher positive predictive values were observed in extra-pelvic lymph nodes and bone compared to viscera/soft tissue

Clinicaltrials.gov: NCT03739684

Presented By: Steven Rowe, MD, Ph.D., Johns Hopkins University School of Medicine, Baltimore, MD

Co-Authors: Michael Gorin, Lawrence Saperstein, Frederic Pouliot, David Josephson, Peter Carroll, Jeffrey Wong, Austin Pantel, Morand Piert, Kenneth Gage, Steve Cho, Andrei Iagaru, Janet Pollard, Vivien Wong, Jessica Jensen, Nancy Stambler, Michael Morris, and Barry Siegel

Written By: Zachary Klaassen, MD, MSc – Urologic Oncologist, Assistant Professor of Urology, Georgia Cancer Center, Augusta University/Medical College of Georgia Twitter: @zklaassen_md at the Society of Nuclear Medicine & Molecular Imaging – 2021 Virtual Meeting, June 11-15, 2021

References:
  1. Morris MJ, Rowe SP, Gorin MA, et al. Diagnostic Performance of 18F-DCFPyL-PET/CT in Men with Biochemically Recurrent Prostate Cancer: Results from the CONDOR Phase III, Multicenter Study. Clin Cancer Res. 2021 Feb 23 [Epub ahead of print].
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