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

Purpose 68 Ga-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 68 Ga-PSMA PET/CT findings. We investigated the value of 18 F-FDG compared with 68 Ga-PSMA and identified BCR patients with 68 Ga-PSMA-negative findings who are most likely to benefit from 18 F-FDG PET/CT. Methods Seventy-two BCR patients with negative 68 Ga-PSMA PET/CT findings were retrospectively identified from 510 patients who underwent concomitant 68 Ga-PSMA and 18 F-FDG PET/CT between June 2018 and August 2020. Patients were categorised into groups with positive or negative 18 F-FDG PET/CT findings. Differences in patients’ characteristics between these two groups and predictors of positive 18 F-FDG findings were analysed. Results The detection rate of 18 F-FDG PET/CT was 16.7% (12/72) in BCR patients with 68 Ga-PSMA-negative findings. PSA and Gleason score were significantly higher in the 18 F-FDG-positive group than in the 18 F-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 18 F-FDG-positive findings ( P < 0.001 and P = 0.015, respectively). The probabilities of 18 F-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 18 F-FDG-positive findings, and BCR patients with 68 Ga-PSMA-negative findings with high PSA and Gleason score are most likely to benefit from 18 F-FDG PET/CT.