Combined value of PSMA-based 18F-DCFPyL, 18F-FDG and 18F-NaF PET/CT imaging in metastatic prostate cancer patients

Objectives: To investigate the combined performance of ¹⁸F-DCFPyL, a Prostate-Specific Membrane Antigen (PSMA) targeted PET agent, ¹⁸F-FDG and ¹⁸F-NaF PET/CT imaging in a prospective cohort of patients with metastatic prostate cancer.

Methods: This is a prospective IRB-approved, single-institution study, including 25 patients with documented metastatic prostate cancer by conventional imaging (average PSA of 65.8 ng/mL, range 0.15-2910 ng/mL). Seventeen patients were castrate-sensitive, and eight patients were castrate-resistant prostate cancer. All patients underwent whole-body ¹⁸F-DCFPyL-PET/CT at 2 h p.i (299.9±15.5 MBq), ¹⁸F-FDG-PET/CT and ¹⁸F-NaF PET/CT imaging about 2 weeks apart. PSMA-PET lesion detection rate and scan concordance were correlated with patient castrate status and treatment status at the time of the scan.

Results: All patients showed a positive ¹⁸F-DCFPyL-PET scan suspicious for metastatic disease: nine patients had soft-tissue disease only, two patients had bone disease only, one patient had lung disease only, and the remainder patients had the presence of bony disease in combination with soft tissue lesions. ¹⁸F-DCFPyL-PET detected higher tumor burden in the group of castrate-resistant compared to the castrate sensitive group of patients (p=0.002). ¹⁸F-DCFPyL and ¹⁸F-FDG PET scans had overall concordant positive findings in 20% of patients, who were mostly castrate-resistant, whereas 80% of patients had incongruent findings with ¹⁸F-DCFPyL detecting significantly more lesions than ¹⁸F-FDG (p < 0.001), except for one patient whose ¹⁸F-FDG detected multiple liver lesions negative on ¹⁸F-DCFPyL. For bone lesions, ¹⁸F-DCFPyL and ¹⁸F-NaF showed good imaging concordance in 60% of patients with osseous lesions, with ¹⁸F-NaF-PET detecting more bone lesions than DCFPyL in 3 patients and ¹⁸F-DCFPyL-PET detected more bone lesions in another 3 patients, while 1 patient had bone disease detected by ¹⁸F-NaF-PET only. The congruence DCFPyL/NaF did not depend on patient’s castrate status or prior treatment exposure. Pathologic confirmation of metastatic disease was performed for at least one positive-DCFPyL lesion in 48% (12/25) of the patients (biopsy sites: 6 bone lesions, 4 prostate bed lesions, 1 supraclavicular LN and 1 lung lesion); three patients are pending biopsy, and the remaining patients either had lesions not amenable to biopsy or who refused biopsy. Patient accrual is ongoing for this trial and more results will be available at the time of presentation.

Conclusions: ¹⁸F-DCFPyL-PET imaging was able to identify suspicious lesions in patients with castrate-sensitive and castrate-resistant metastatic prostate cancer. ¹⁸F-DCFPyL-PET detected significantly more lesions than ¹⁸F-FDG-PET, although there was good DCFPyL/FDG PET imaging concordance in 20% of the cases, particularly in the setting of metastatic castrate-resistant prostate cancer. DCFPyL/NaF showed good imaging concordance in 60% of the patients with bone lesions, independent of the patient’s castration status or treatment status.