The Added Value of 18F-FDG PET/CT Compared with 68Ga-PSMA PET/CT in Patients with Castration-Resistant Prostate Cancer

68Ga-prostate-specific membrane antigen (68Ga-PSMA) PET/CT is a commonly used imaging modality in prostate cancers. However, few studies have compared the diagnostic efficiency between 68Ga-PSMA and 18F-FDG PET/CT and evaluated whether a heterogeneous metabolic phenotype (especially 68Ga-PSMA–negative [−], 18F-FDG–positive [+] lesions) exists in patients with castration-resistant prostate cancer (CRPC). We determined the added value of 18F-FDG PET/CT compared with 68Ga-PSMA PET/CT in CRPC patients and identified CRPC patients who may benefit from additional 18F-FDG PET/CT. Methods: The data of 56 patients with CRPC who underwent both 68Ga-PSMA and 18F-FDG PET/CT from May 2018 to February 2021 were retrospectively analyzed. The patients were classified into 2 groups: with or without 68Ga-PSMA−, 18F-FDG+ lesions. The differences in patient characteristics between the 2 groups and predictors of patients who have at least 1 68Ga-PSMA−, 18F-FDG+ lesion were analyzed. Results: Although both the detection rate (75.0% vs. 51.8%, P = 0.004) and the number of positive lesions (135 vs. 95) were higher for 68Ga-PSMA PET/CT than for 18F-FDG PET/CT, there were still 13 of 56 (23.2%) patients with at least 1 68Ga-PSMA−, 18F-FDG+ lesion. Prostate-specific antigen (PSA) and the Gleason score were both higher in patients with 68Ga-PSMA−, 18F-FDG+ lesions than in those without (P = 0.04 and P