Immunohistochemical and histopathological validation of 18 F-PSMA-1007 PET/CT for intraprostatic cancerous lesions.

INTRODUCTION: Prostate-specific membrane antigen (PSMA) is overexpressed in prostate cancer (PCa). In this study, we aim to immunohistochemically and histopathological validate the fluorine-18 (18 F)-PSMA-1007 positron emission tomography/computed tomography (PET/CT) for intraprostatic PCa lesions. METHODS: Between February 2019 and October 2020, patients with biopsy-proven, treatment-naïve intermediate-to-high-risk PCa undergoing an 18 F-PSMA-1007 PET/CT before robot-assisted radical prostatectomy (RARP) were prospectively enrolled. For all PCa lesions found on whole-mount histopathology, location, size, International Society of Urological Pathology (ISUP) grade group (GG), and immune reactive score (IRS) were assessed after PSMA staining. ISUP GG ≥ 3 PCa was defined as clinically significant (cs) PCa. All lesions were matched on PSMA PET/CT and the maximum standardized uptake value (SUVmax) was measured. RESULTS: A total of 125 lesions were analyzed in the 80 RARP specimens, of which 49 (40%) were csPCa and 76 (60%) non-csPCa. Linear multivariable regressions showed that an increase in SUVmax significantly correlated with a higher ISUP GG (p values between 0.021 and 0.001) and a higher IRS (p = 0.017). Logistic multivariable regression showed that csPCa significantly correlated with a higher SUVmax (odds ratio, OR: 1.17 [95% confidence interval, CI: 1.04-1.21, p = 0.005]), an increase in tumor length (OR: 1.05 [95% CI 1.01-1.10, p = 0.020]) and a higher IRS (OR; 1.24 [95% CI 1.07-1.47, p = 0.006]). A SUVmax threshold of 4 would have resulted in one (2%) missed lesion with csPCa. CONCLUSION: This prospective study revealed that 18 F-PSMA-1007 PET/CT SUVmax is correlated with the ISUP GG and IRS, and thereby could be a tool to characterize intraprostatic PCa lesions.

Diagnostic accuracy of 18F-fluciclovine PET/CT in primary lymph node staging of prostate cancer.

INTRODUCTION: To determine preoperative diagnostic accuracy of 18F-fluciclovine PET/CT-scan in detection (or exclusion) of lymph node metastases (LNM) in men with prostate cancer (PCa) in comparison to the histopathological results of the extended pelvic lymph node dissection (e-PLND). METHODS: A retrospective medical records-based cohort study, including 47 men with primary PCa who received 18F-fluciclovine PET/CT and subsequent e-PLND for lymph node staging. Incidence and number of visualized LNM, their locations and diameters on 18F-fluciclovine PET/CT were recorded in comparison to the histopathological results of the e-PLND as reference. Positive predictive value (PPV), negative predictive value (NPV), sensitivity, specificity and diagnostic accuracy of 18F-fluciclovine PET/CT were calculated on the basis of histopathology results after e-PLND. RESULTS: Forty-seven men were eligible for analysis. Median lymph node yield was 19 (range 10-70). A total of 996 lymph nodes were removed, and 59 metastases were found in 21 cases (45%). Preoperative PET was issued 'positive' in 11 men and in 9 of them (82%) this was histopathologically confirmed resulting in a PPV of 82% (95% CI, 51-96). On the contrary, PET was issued 'negative' in 36 cases, but in 12 of them (33%) metastases were detected in the e-PLND specimen, resulting in an NPV of 67% (95% CI, 50-80). The patient-based sensitivity was 43% (95% CI, 24-64) and the patient-based specificity rate was 92% (95% CI, 75-99), whereas overall diagnostic accuracy was established to be 70% in the present cohort. CONCLUSION: 18F-Fluciclovine PET/CT has a high specificity and positive predicted value for the presence of LNM in men with prostate cancer. However, the sensitivity and NPV seem to be limited to exclude the absence of LNM at a clinically acceptable level. Prospective evaluation is necessary to define patients who may benefit from 18F-fluciclovine PET/CT as a triage test for the indication for e-PLND.