Does focal incidental ¹⁸F-FDG PET/CT uptake in the prostate have significance?

¹⁸F-FDG PET/CT is used to characterize many malignancies, but is not recommended for localized prostate cancer. This study explores the value of multi-parametric MRI (mpMRI) in characterizing incidental prostate ¹⁸F-FDG uptake.

Thirty-one patients who underwent ¹⁸F-FDG PET/CT for reasons unrelated to prostate cancer and prostate mpMRI were eligible for this retrospective study. The mpMRI included T2-weighted (T2W), dynamic contrast enhancement (DCE), apparent diffusion coefficient (ADC), and MR spectroscopy (MRS) sequences. Fourteen patients were excluded (n = 8 insufficient histopathology, n = 6 radical prostatectomy before PET), and final analysis included 17 patients. A nuclear medicine physician, blinded to clinicopathologic findings, identified suspicious areas and maximum standardized uptake values (SUVmax) on ¹⁸F-FDG PET/CT. Sector-based imaging findings were correlated with annotated histopathology from whole-mount or MRI/transrectal ultrasound 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.

The PPV of ¹⁸F-FDG PET alone in detecting prostate cancer was 0.65. Combining ¹⁸F-FDG PET as a base parameter with mpMRI (T2W, DCE, ADC, and MRS) increased the PPV to 0.82, 0.83, 0.83, and 0.94, respectively. All benign lesions had SUVmax < 6. Malignant lesions had higher SUVmax values that correlated with Gleason scores. There was a significant difference in SUVmax per prostate between the Gleason ≥ 4 + 5 and benign categories (p = 0.03).

Focal incidental prostate ¹⁸F-FDG uptake has low clinical utility alone, but regions of uptake may harbor high-grade prostate cancer, especially if SUVmax > 6. Using mpMRI to further evaluate incidental ¹⁸F-FDG uptake aids the diagnosis of prostate cancer.