Does incidental FDG PET uptake in the prostate have significance?

Abstract

115 Background: 18F-FDG PET/CT is widely used to diagnose malignancy, but is not recommended for localized prostate cancer. This study explores the value of multi-parametric MRI (mpMRI) in characterizing incidentally detected prostate FDG uptake. Methods: Thirty-one patients who underwent FDG PET/CT and prostate MRI were eligible for this study. 14 patients were excluded (n=8 insufficient histopathology, n=6 radical prostatectomy before PET), with final analysis of 17 patients. The mpMRI sequences included T2-weighted, dynamic contrast enhancement (DCE), apparent diffusion coefficient (ADC), and MR spectroscopy (MRS). Nuclear medicine physicians, blinded to clinicopathologic findings, identified suspicious areas and maximum standardized uptake values (SUVmax) on FDG PET/CT. The lesion and sector-based imaging findings were correlated with annotated histopathology from whole-mount or MRI/TRUS fusion biopsy samples. Positive predictive values (PPVs) were estimated using generalized estimating equations with logit link. Results were evaluated with Kruskal-Wallis and Dunn’s multiple comparisons tests. Results: The PPV of FDG PET alone in detecting prostate cancer was 0.56. Combining FDG (base parameter) with mpMRI modalities (T2, DCE, ADC, MRS) increased the sector-based PPV to 0.79, 0.82, 0.80, and 0.89, respectively. All benign lesions had SUVmax < 5, and malignant lesions had higher mean SUVmax values that correlated with Gleason scores [Table]. This relationship between SUVmax and Gleason score was significant, with p=0.012 on the Kruskal-Wallis test and p=0.015 on the Dunn’s multiple comparisons test for Gleason 0 vs Gleason ≥ 4+5. Conclusions: Incidental prostate FDG uptake has low clinical utility alone, but these areas may harbor high-grade prostate cancer, especially if the SUVmax is greater than 5. [Table: see text]