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

Abstract

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. <b>Methods:</b> 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. <b>Results:</b> Although both the detection rate (75.0% vs. 51.8%, <i>P</i> = 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 (<i>P</i> = 0.04 and <i>P</i> &lt; 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 ⁶⁸Ga-PSMA−, ¹⁸F-FDG+ lesions (<i>P</i> = 0.01 and <i>P</i> = 0.04, respectively). The incidences of having ⁶⁸Ga-PSMA−, ¹⁸F-FDG+ lesions in low-probability (Gleason score &lt; 8 and PSA &lt; 7.9 ng/mL), medium-probability (Gleason score ≥ 8 and PSA &lt; 7.9 ng/mL or Gleason score &lt; 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 (<i>P</i> &lt; 0.001). <b>Conclusion:</b> Gleason score and PSA are significant predictors of ⁶⁸Ga-PSMA−, ¹⁸F-FDG+ lesions, and CRPC patients with a high Gleason score and PSA may benefit from additional ¹⁸F-FDG PET/CT.

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