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

Ga-68-prostate-specific membrane antigen (Ga-68-PSMA) PET/CT is a commonly used imaging modality in prostate cancers. However, few studies have compared the diagnostic efficiency between Ga-68-PSMA and F-18-FDG PET/CT and evaluated whether a heterogeneous metabolic phenotype (especially Ga-68-PSMA-negative [-], F-18-FDG-positive [+] lesions) exists in patients with castration-resistant prostate cancer (CRPC). We determined the added value of F-18-FDG PET/CT compared with Ga-68-PSMA PET/CT in CRPC patients and identified CRPC patients who may benefit from additional F-18-FDG PET/CT. Methods: The data of 56 patients with CRPC who underwent both Ga-68-PSMA and F-18-FDG PET/CT from May 2018 to February 2021 were retrospectively analyzed. The patients were classified into 2 groups: with or without Ga-68-PSMA -, F-18-FDG+ lesions. The differences in patient characteristics between the 2 groups and predictors of patients who have at least 1( 68)Ga-PSMA -, F-18-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 Ga-68-PSMA PET/CT than for F-18-FDG PET/CT, there were still 13 of 56 (23.2%) patients with at least 1 Ga-68-PSMA-, F-18-FDG+ lesion. Prostate-specific antigen (PSA) and the Gleason score were both higher in patients with Ga-68-PSMA -, F-18-FDG+ lesions than in those without (P = 0.04 and P < 0.001, respectively). Multivariate regression analysis showed that the Gleason score (>= 8) and PSA (>= 7.9 ng/mL) were associated with the detection rate of patients who had Ga-68-PSMA -, F-18-FDG+ lesions (P = 0 .01 and P = 0.04, respectively). The incidences of having Ga-68-PSMA-, F-18-FDG+ lesions in low-probability (Gleason score <8 and PSA < 7.9 ng/mL), medium-probability (Gleason score >= 8 and PSA < 7.9 ng/mL or Gleason score < 8 and PSA 7.9 ng/mL), and high-probability (Gleason score >= 8 and PSA >= 7.9 ng/mL) groups were 0%, 21.7%, and 61.5%, respectively (P < 0.001). Conclusion: Gleason score and PSA are significant predictors of Ga-68-PSMA -, F-18-FDG+ lesions, and CRPC patients with a high Gleason score and PSA may benefit from additional F-18-FDG PET/CT.