Utility of 18F-Fluciclovine PET/MRI for Staging Newly Diagnosed High-Risk Prostate Cancer and Evaluating Response to Initial Androgen Deprivation Therapy: A Prospective Single-Arm Pilot Study

BACKGROUND. Despite advances in prostate cancer treatment, rates of biochemical recurrence remain high, relating to lack of detection of small-volume metastatic disease using conventional imaging for initial staging. OBJECTIVE. The purpose of this study was to assess the potential use of (18)F-fluciclovine PET/MRI for initial staging of high-risk prostate cancer and evaluating response to androgen deprivation therapy (ADT). METHODS. This prospective clinical trial enrolled 14 men with newly diagnosed high-risk prostate cancer and negative or equivocal conventional staging imaging for metastatic disease between January 2018 and February 2019. All patients underwent pretreatment (18)F-fluciclovine PET/MRI including multiparametric prostate MRI; 12 underwent (18)F-fluciclovine PET/MRI after surgery or between ADT and radiotherapy. Confidence in identification of the primary intraprostatic lesion and nodal metastases was independently rated on a 0–3 Likert scale by three readers with nuclear medicine experience for (18)F-fluciclovine PET/MRI and three readers with abdominal imaging experience for MRI alone. Findings scored as 2 or 3 by at least two readers of a given modality were considered positive. A single reader measured SUV(mean), SUV(max), and volume of the MRI-defined intraprostatic lesion and SUV(max) of suspicious lymph nodes on PET before and after initiation of ADT. Changes in SUV were analyzed using nonparametric Wilcoxon signed-rank tests. RESULTS. The biopsy-proven lesion in the prostate gland was accurately identified in all 14 patients on both MRI and (18)F-fluciclovine PET/MRI. Suspected nodal metastases were detected in three patients on MRI and seven patients on (18)F-fluciclovine PET/MRI. After ADT, all patients showed decreased activity within the intraprostatic lesion and/or all suspicious lymph nodes. The primary lesion SUV(mean) was 4.5 ± 1.1 (range, 2.7–6.5) before treatment and 2.4 ± 1.1 (range, 0.0–3.6) after initiation of ADT (p = .008). For suspicious lymph nodes, the pretreatment SUV(max) was 5.5 ± 3.7 (range, 2.8–12.7) and the posttreatment SUV(max) was 2.8 ± 1.4 (range, 1.4–5.5) (p = .03). CONCLUSION. (18)F-labeled fluciclovine PET/MRI shows potential utility in initial staging of high-risk prostate cancer and in evaluating response to ADT. CLINICAL IMPACT. Given the FDA approval and widespread availability of (18)F-fluciclovine, the findings could have an impact in the immediate future in guiding initial management of patients with prostate cancer. TRIAL REGISTRATION. ClinicalTrials.gov NCT03264456