A comparison of prostate cancer bone metastases on F-Sodium Fluoride and Prostate Specific Membrane Antigen (F-PSMA) PET/CT: Discordant uptake in the same lesion.

PURPOSE

Prostate-Specific Membrane Antigen (PSMA) PET/CT has been introduced as a sensitive method for characterizing metastatic prostate cancer. The purpose of this study is to compare the spatial concordance of F-NaF PET/CT and F-PSMA-targeted PET/CT within prostate cancer bone metastases.

METHODS

Prostate cancer patients with known bone metastases underwent PSMA-targeted PET/CT (F-DCFBC or F-DCFPyL) and F-NaF PET/CT. In pelvic and spinal lesions detected by both radiotracers, regions-of-interest (ROIs) derived by various thresholds of uptake intensity were compared for spatial colocalization. Overlap volume was correlated with uptake characteristics and disease status.

RESULTS

The study included 149 lesions in 19 patients. Qualitatively, lesions exhibited a heterogeneous range of spatial concordance between PSMA and NaF uptake from completely matched to completely discordant. Quantitatively, overlap volume decreased as a function of tracer intensity. and disease status, where lesions from patients with castration-sensitive disease showed higher spatial concordance while lesions from patients with castration-resistant disease demonstrated more frequent spatial discordance.

CONCLUSION

As metastatic prostate cancer progresses from castration-sensitive to castration-resistant, greater discordance is observed between NaF PET and PSMA PET uptake. This may indicate a possible phenotypic shift to tumor growth that is more independent of bone remodeling via osteoblastic formation.