18F-DCFPyL, PSMA-Targeted PET Imaging Agent, Provokes High CLR and PPV

Frédéric Pouliot, MD, PhD

Localized metastatic lesions were detected with a high correct localization rate (CLR) and positive predictive value (PPV) with the investigational prostate-specific membrane antigen (PSMA)–targeted PET imaging agent ¹⁸F-DCFPyL, according to data from the pivotal phase 3 CONDOR study

The data were reported at the 2021 Genitourinary Cancers Symposium as the FDA prepares to make a decision on a new drug application (NDA) for the prostate-specific membrane antigen (PSMA) PET imaging agent.¹

The multicenter phase 3 CONDOR study (NCT03739684) enrolled men with rising prostate-specific antigen (PSA) after definitive therapy and negative or equivocal standard-of-care imaging. Patients were required to have a PSA level of 0.2 or higher if they had undergone radical prostatectomy (RP) or a PSA level of 2.0 or higher if they were treated with radiation therapy or cryotherapy.

The radiolabeled small molecule ¹⁸F-DCFPyL targets the extracellular domain of PSMA. Imaging is supposed to begin 1 to 2 hours following intravenous administration of ¹⁸F-DCFPyL as bolus injection.

The primary end point of the study was CLR, defined as percentage of patients with a 1:1 correspondence between at least 1 lesion identified by Peel–PET/CT and the composite standard of truth (SOT; N = 132: pathology, correlative imaging, or PSA response). Peel scans were read by 3 blinded independent central readers. The key secondary end point was the percentage of patients in whom ¹⁸F-DCFPyL PET/CT led to a change in intended treatment.

Overall, there were 208 evaluable patients, about 85% of whom underwent RP, either alone or with radiation. Median PSA level of the cohort was 0.8 ng/mL, and 68.8% had a PSA level lower than 2.0 ng/mL. Some 27.9% had received at least 1 prior systemic therapy. Detection of disease as manifested by a positive ¹⁸F-DCFPyL–PET/CT scan was 65.9%, 59.6%, and 59.1% by the 3 readers.

The prespecified criterion for CLR success was for the lower limit of the 95% CI to exceed 20% for at least 2 of the 3 readers. For every reader, the lower bound of the 95% CI for the CLR was well in excess of the 20% benchmark, meeting the primary end point of the study.

The CLRs were 85.6% (95% CI, 78.8%-92.3%), 87.0% (95% CI, 80.4%-93.6%), and 84.8% (95% CI, 77.8%-91.9%) by the 3 readers.

PPV was also high, with a range of 88.7% to 90.7% across all 3 readers. Further, the high CLR and PPV were maintained across all 3 categories of SOT. For histopathology (n = 31) the CLR ranges were 78.6 to 82.8% and the PPV ranges were 92.9% to 93.3%. For correlative imaging (n = 100) the ranges were 86.1% to 88.6% and 87.% to 89.5%, respectively. The ranges were both 100% for PSA response.

“PSMA-targeted 18F-DCFPyL-PET/CT detected and localized metastatic lesions with high CLR and PPV regardless of which criterion defined CLR that was used, in men with BCR who had negative or equivocal baseline standard imaging,” first study author Frederic Pouliot, MD, PhD, assistant professor, Department of Surgery, Faculty of Medicine, Université Lavaland, Quebec, Canada, and coauthors wrote.

Regarding the secondary end point of treatment change, as measured through pre- and post-PET questionnaires, 63.9% of evaluable patients had a change in intended management due to ¹⁸F-DCFPyL-PET/CT. Of these changes, 78.6% were triggered by positive ¹⁸F-DCFPyL-PET/CT findings and 21.4% were caused by negative findings.

The changes included 58 patients switching from salvage local therapy to systemic therapy, 49 patients changing from observation to initiating therapy, 43 patients switching from noncurative systemic therapy to salvage local therapy, and 9 patients scaling back from planned treatment to observation.

The NDA for ¹⁸F-DCFPyL-PET/CT being considered by the FDA also includes supportive data from the phase 2/3 OSPREY trial, in which ¹⁸F-DCFPyL-PET/CT was assessed in 2 patient cohorts.² Cohort A included men with high-risk, locally advanced prostate cancer, and the researchers assessed the capacity of ¹⁸F-DCFPyL-PET/CT to detect prostate cancer in pelvic lymph nodes. Cohort B comprised patients with metastatic or recurrent disease and the researchers examined the performance of ¹⁸F-DCFPyL-PET/CT in detecting distant metastases.

In cohort A, results for ¹⁸F-DCFPyL-PET/CT in detecting disease in pelvic lymph nodes showed a specificity of 96% to 99%, a sensitivity of 31% to 42%, and a PPV of 78% to 91%. The sensitivity and PPV rates for detecting metastatic lesions in cohort B were 93% to 99% and 81% to 88%, respectively.

_References

_{1. Pouliot F, Gorin MA, Rowe SP, et al. PSMA-targeted imaging with 18F-DCFPyL-PET/CT in patients (pts) with biochemically recurrent prostate cancer (PCa): A phase III study (CONDOR)—A subanalysis of correct localization rate (CLR) and positive predictive value (PPV) by standard of truth. J Clin Oncol. 2021;39(suppl 6):33. doi: 10.1200/JCO.2021.39.6_suppl.33}

_{2. PDUFA action date of May 28, 2021 assigned by U.S. Food and Drug Administration. Published online December 9, 2020. https://bit.ly/2KtYerG. Accessed February 13, 2021}