Diagnostic value of 18F-FDG PET/CT in patients with biochemical recurrent prostate cancer and negative 68Ga-PSMA PET/CT

Purpose Ga-68-PSMA PET/CT has a high detection rate in prostate cancer patients with biochemical recurrence (BCR). However, few studies have reported other imaging methods for BCR with negative Ga-68-PSMA PET/CT findings. We investigated the value of F-18-FDG compared with Ga-68-PSMA and identified BCR patients with Ga-68-PSMA-negative findings who are most likely to benefit from F-18-FDG PET/CT. Methods Seventy-two BCR patients with negative Ga-68-PSMA PET/CT findings were retrospectively identified from 510 patients who underwent concomitant Ga-68-PSMA and F-18-FDG PET/CT between June 2018 and August 2020. Patients were categorised into groups with positive or negative F-18-FDG PET/CT findings. Differences in patients' characteristics between these two groups and predictors of positive F-18-FDG findings were analysed. Results The detection rate of F-18-FDG PET/CT was 16.7% (12/72) in BCR patients with Ga-68-PSMA-negative findings. PSA and Gleason score were significantly higher in the F-18-FDG-positive group than in the F-18-FDG-negative group (P < 0.001 and P < 0.001, respectively). A multivariate analysis indicated that PSA (PSA >= 2.3 ng/mL) and Gleason score (Gleason score >= 8) correlated with F-18-FDG-positive findings (P < 0.001 and P = 0.015, respectively). The probabilities of F-18-FDG-positive findings in the low-potential (PSA <2.3 ng/mL and Gleason score <8), moderate-potential (PSA <2.3 ng/mL and Gleason score >= 8 or PSA >= 2.3 ng/mL and Gleason score <8), and high-potential (PSA >= 2.3 ng/mL and Gleason score >= 8) groups were 0%, 11.5%, and 90.0%, respectively (P < 0.001). Conclusion PSA level and Gleason score are independent predictors of F-18-FDG-positive findings, and BCR patients with Ga-68-PSMA-negative findings with high PSA and Gleason score are most likely to benefit from F-18-FDG PET/CT.