Staging of Nonmetastatic Relapsed Prostate Cancer May Be Aided by PSMA-Directed PET Tracer

A novel prostate-specific membrane antigen (PSMA)–targeted radiopharmaceutical for positron emission tomography (PET) known as ¹⁸F-DCFPyL, may help to identify occult prostate cancer and more accurately characterize disease burden, according to a subanalysis of the OSPREY trial presented at the 2021 Genitourinary Cancers Symposium.

“¹⁸F-DCFPyL-PET/CT identified M1 disease in the majority of patients examined who otherwise had locoregional disease,” the researchers wrote. “These data suggest that ¹⁸F-DCFPyL-PET/CT may be a useful tool in properly staging men with both metastatic and nonmetastatic relapsed disease, which could lead to superior treatment paradigms than currently exist using conventional imaging.”

In the poster presentation, Jeremy C. Durack, MD, MS, interventional radiologist, Memorial Sloan Kettering Cancer Center, noted that previous topline results demonstrated the following:

• ¹⁸F-DCFPyL helped to identify recurrent/metastatic prostate cancer, with a positive predictive value (PPV) of 82% and sensitivity of 96%.
• ¹⁸F-DCFPyL demonstrated a 40% sensitivity rate, compared to 40% with conventional imaging, as well as a high PPC (87%), an 83% net present value, and 98% specificity in men at high risk for metastatic prostate cancer.
• 18F-DCFPyL facilitated initial therapy for patients.

In the prospective phase 2/3 study OSPREY study (NCT02981368), conducted across 10 sites in the US and Canada, Durack and colleagues evaluated ¹⁸F-DCFPyL in 385 patients broken into 2 cohorts: cohort A (men with high-risk prostate cancer per National Comprehensive Cancer Network guidelines) and cohort B (men with presumptive recurrent or metastatic prostate cancer based on radiologic findings).

The bolus intravenous injection of ¹⁸F-DCFPyL was administered at 9 mCI (333 MBq), with imaging beginning 1 to 2 hours after administration.

¹⁸F-DCFPyL detection rates were systematically analyzed. The prospective analysis included 3 blinded, independent ¹⁸F-DCFPyL-PET/CT readers and 1 blinded conventional imaging reader.

In their poster presentation, the researchers reported on cohort B, in which ¹⁸F-DCFPyL-PET/CT was evaluated in 117 men with radiologic evidence of local recurrence or metastatic disease on baseline anatomical imaging, including a CT scan or MRI, or whole-body bone scintigraphy and in whom at least 1 lesion was deemed amenable to biopsy.

Key efficacy end points from cohort B included sensitivity of ¹⁸F-DCFPyL imaging within metastatic lesions relative to histopathology, positive predictive value (PPV) within metastatic lesions, and detection rates between 18F-DCFPyL and conventional imaging.

At baseline, 82 patients (71%) had radiographic M1 stage disease, including 14 patients with M1a, 50 patients with M1b, 18 patients with M1c; 33 patients (29%) were M0 stage at baseline by central conventional imaging review; and 2 patients were unevaluable. In addition, 28% (n = 32) had PSA <2.0 ng/mL.

Of the 33 patients with M0 stage using conventional imaging, 18F-DCFPyL up-staged 19 (58%) men to M1 stage. Ten (91%) of 11 men underwent an extra-pelvic biopsy and were confirmed to have M1 disease by pathology, including 9 patients with M1b and 1 patient with M1a.

Of the 82 patients with M1 stage at baseline using conventional imaging, ¹⁸F-DCFPyL up-staged 10 men (12%) to a higher M1 sub-stage, including 4 patients from M1a to M1b or M1c and 6 patients from M1b to M1c. Moreover, ¹⁸F-DCFPyL down-staged 18 men (22%) to M0 in this group.

“Conventional imaging and bone scintigraphy are suboptimal modalities for identifying (prostate cancer),” the researchers wrote. “PSMA-based imaging is highly promising for (prostate cancer) detection. ¹⁸F-DCFPyL is a novel PSMA-targeted radiopharmaceutical for PET that may be useful in staging of (prostate cancer).”

_Reference

_{Durack JC, Alva AS, Preston MA, et al. A prospective phase II/III study of PSMA-targeted 18F-DCFPyL-PET/CT in patients (pts) with prostate cancer (PCa) (OSPREY): A subanalysis of disease staging changes in PCa pts with recurrence or metastases on conventional imaging. Presented at: 2021 Genitourinary Cancers Symposium; February 11-13, 2021; Virtual. Abstract 32.}